docs: fix stub pages and improve docs structure (#2101)
Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com>
This commit is contained in:
Felix Weinberger
GitHub
parent
c86477c7b7
commit
1f9fb348f3
10 changed files with 696 additions and 728 deletions
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@ -170,7 +170,6 @@ The [Model Context Protocol (MCP)](https://modelcontextprotocol.io) lets you bui
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- [Authorization](docs/authorization.md) -- OAuth 2.1, token verification, client authentication
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- [Low-Level Server](docs/low-level-server.md) -- direct handler registration for advanced use cases
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- [Protocol Features](docs/protocol.md) -- MCP primitives, server capabilities
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- [Concepts](docs/concepts.md) -- architecture overview
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- [Testing](docs/testing.md) -- in-memory transport testing with pytest
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- [API Reference](https://modelcontextprotocol.github.io/python-sdk/api/)
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- [Experimental Features (Tasks)](https://modelcontextprotocol.github.io/python-sdk/experimental/tasks/)
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@ -1,5 +1,177 @@
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# Authorization
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!!! warning "Under Construction"
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This page covers OAuth 2.1 authentication for both MCP servers and clients.
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This page is currently being written. Check back soon for complete documentation.
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## Server-Side Authentication
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Authentication can be used by servers that want to expose tools accessing protected resources.
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`mcp.server.auth` implements OAuth 2.1 resource server functionality, where MCP servers act as Resource Servers (RS) that validate tokens issued by separate Authorization Servers (AS). This follows the [MCP authorization specification](https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization) and implements RFC 9728 (Protected Resource Metadata) for AS discovery.
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MCP servers can use authentication by providing an implementation of the `TokenVerifier` protocol:
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<!-- snippet-source examples/snippets/servers/oauth_server.py -->
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```python
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"""
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Run from the repository root:
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uv run examples/snippets/servers/oauth_server.py
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"""
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from pydantic import AnyHttpUrl
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from mcp.server.auth.provider import AccessToken, TokenVerifier
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from mcp.server.auth.settings import AuthSettings
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from mcp.server.fastmcp import FastMCP
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class SimpleTokenVerifier(TokenVerifier):
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"""Simple token verifier for demonstration."""
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async def verify_token(self, token: str) -> AccessToken | None:
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pass # This is where you would implement actual token validation
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# Create FastMCP instance as a Resource Server
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mcp = FastMCP(
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"Weather Service",
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json_response=True,
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# Token verifier for authentication
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token_verifier=SimpleTokenVerifier(),
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# Auth settings for RFC 9728 Protected Resource Metadata
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auth=AuthSettings(
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issuer_url=AnyHttpUrl("https://auth.example.com"), # Authorization Server URL
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resource_server_url=AnyHttpUrl("http://localhost:3001"), # This server's URL
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required_scopes=["user"],
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),
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)
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@mcp.tool()
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async def get_weather(city: str = "London") -> dict[str, str]:
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"""Get weather data for a city"""
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return {
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"city": city,
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"temperature": "22",
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"condition": "Partly cloudy",
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"humidity": "65%",
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}
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if __name__ == "__main__":
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mcp.run(transport="streamable-http")
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```
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_Full example: [examples/snippets/servers/oauth_server.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/oauth_server.py)_
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<!-- /snippet-source -->
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For a complete example with separate Authorization Server and Resource Server implementations, see [`examples/servers/simple-auth/`](examples/servers/simple-auth/).
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**Architecture:**
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- **Authorization Server (AS)**: Handles OAuth flows, user authentication, and token issuance
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- **Resource Server (RS)**: Your MCP server that validates tokens and serves protected resources
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- **Client**: Discovers AS through RFC 9728, obtains tokens, and uses them with the MCP server
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See [TokenVerifier](src/mcp/server/auth/provider.py) for more details on implementing token validation.
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## Client-Side Authentication
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The SDK includes [authorization support](https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization) for connecting to protected MCP servers:
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<!-- snippet-source examples/snippets/clients/oauth_client.py -->
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```python
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"""
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Before running, specify running MCP RS server URL.
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To spin up RS server locally, see
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examples/servers/simple-auth/README.md
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cd to the `examples/snippets` directory and run:
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uv run oauth-client
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"""
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import asyncio
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from urllib.parse import parse_qs, urlparse
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import httpx
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from pydantic import AnyUrl
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from mcp import ClientSession
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from mcp.client.auth import OAuthClientProvider, TokenStorage
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from mcp.client.streamable_http import streamable_http_client
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from mcp.shared.auth import OAuthClientInformationFull, OAuthClientMetadata, OAuthToken
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class InMemoryTokenStorage(TokenStorage):
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"""Demo In-memory token storage implementation."""
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def __init__(self):
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self.tokens: OAuthToken | None = None
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self.client_info: OAuthClientInformationFull | None = None
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async def get_tokens(self) -> OAuthToken | None:
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"""Get stored tokens."""
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return self.tokens
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async def set_tokens(self, tokens: OAuthToken) -> None:
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"""Store tokens."""
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self.tokens = tokens
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async def get_client_info(self) -> OAuthClientInformationFull | None:
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"""Get stored client information."""
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return self.client_info
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async def set_client_info(self, client_info: OAuthClientInformationFull) -> None:
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"""Store client information."""
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self.client_info = client_info
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async def handle_redirect(auth_url: str) -> None:
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print(f"Visit: {auth_url}")
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async def handle_callback() -> tuple[str, str | None]:
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callback_url = input("Paste callback URL: ")
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params = parse_qs(urlparse(callback_url).query)
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return params["code"][0], params.get("state", [None])[0]
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async def main():
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"""Run the OAuth client example."""
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oauth_auth = OAuthClientProvider(
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server_url="http://localhost:8001",
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client_metadata=OAuthClientMetadata(
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client_name="Example MCP Client",
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redirect_uris=[AnyUrl("http://localhost:3000/callback")],
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grant_types=["authorization_code", "refresh_token"],
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response_types=["code"],
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scope="user",
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),
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storage=InMemoryTokenStorage(),
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redirect_handler=handle_redirect,
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callback_handler=handle_callback,
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)
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async with httpx.AsyncClient(auth=oauth_auth, follow_redirects=True) as custom_client:
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async with streamable_http_client("http://localhost:8001/mcp", http_client=custom_client) as (read, write, _):
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async with ClientSession(read, write) as session:
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await session.initialize()
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tools = await session.list_tools()
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print(f"Available tools: {[tool.name for tool in tools.tools]}")
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resources = await session.list_resources()
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print(f"Available resources: {[r.uri for r in resources.resources]}")
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def run():
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asyncio.run(main())
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if __name__ == "__main__":
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run()
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```
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_Full example: [examples/snippets/clients/oauth_client.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/clients/oauth_client.py)_
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<!-- /snippet-source -->
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For a complete working example, see [`examples/clients/simple-auth-client/`](examples/clients/simple-auth-client/).
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114
docs/client.md
114
docs/client.md
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@ -1,6 +1,6 @@
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# Writing MCP Clients
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The SDK provides a high-level client interface for connecting to MCP servers using various [transports](https://modelcontextprotocol.io/specification/2025-03-26/basic/transports):
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The SDK provides a high-level client interface for connecting to MCP servers using various [transports](https://modelcontextprotocol.io/specification/2025-11-25/basic/transports):
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<!-- snippet-source examples/snippets/clients/stdio_client.py -->
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```python
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@ -68,7 +68,7 @@ async def run():
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# Read a resource (greeting resource from fastmcp_quickstart)
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resource_content = await session.read_resource(AnyUrl("greeting://World"))
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content_block = resource_content.contents[0]
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if isinstance(content_block, types.TextContent):
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if isinstance(content_block, types.TextResourceContents):
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print(f"Resource content: {content_block.text}")
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# Call a tool (add tool from fastmcp_quickstart)
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@ -92,7 +92,7 @@ if __name__ == "__main__":
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_Full example: [examples/snippets/clients/stdio_client.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/clients/stdio_client.py)_
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<!-- /snippet-source -->
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Clients can also connect using [Streamable HTTP transport](https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http):
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Clients can also connect using [Streamable HTTP transport](https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http):
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<!-- snippet-source examples/snippets/clients/streamable_basic.py -->
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```python
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@ -215,107 +215,9 @@ The `get_display_name()` function implements the proper precedence rules for dis
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This ensures your client UI shows the most user-friendly names that servers provide.
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## OAuth Authentication for Clients
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## OAuth Authentication
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The SDK includes [authorization support](https://modelcontextprotocol.io/specification/2025-03-26/basic/authorization) for connecting to protected MCP servers:
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<!-- snippet-source examples/snippets/clients/oauth_client.py -->
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```python
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"""
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Before running, specify running MCP RS server URL.
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To spin up RS server locally, see
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examples/servers/simple-auth/README.md
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cd to the `examples/snippets` directory and run:
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uv run oauth-client
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"""
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import asyncio
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from urllib.parse import parse_qs, urlparse
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import httpx
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from pydantic import AnyUrl
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from mcp import ClientSession
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from mcp.client.auth import OAuthClientProvider, TokenStorage
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from mcp.client.streamable_http import streamable_http_client
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from mcp.shared.auth import OAuthClientInformationFull, OAuthClientMetadata, OAuthToken
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class InMemoryTokenStorage(TokenStorage):
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"""Demo In-memory token storage implementation."""
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def __init__(self):
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self.tokens: OAuthToken | None = None
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self.client_info: OAuthClientInformationFull | None = None
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async def get_tokens(self) -> OAuthToken | None:
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"""Get stored tokens."""
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return self.tokens
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async def set_tokens(self, tokens: OAuthToken) -> None:
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"""Store tokens."""
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self.tokens = tokens
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async def get_client_info(self) -> OAuthClientInformationFull | None:
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"""Get stored client information."""
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return self.client_info
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async def set_client_info(self, client_info: OAuthClientInformationFull) -> None:
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"""Store client information."""
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self.client_info = client_info
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async def handle_redirect(auth_url: str) -> None:
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print(f"Visit: {auth_url}")
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async def handle_callback() -> tuple[str, str | None]:
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callback_url = input("Paste callback URL: ")
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params = parse_qs(urlparse(callback_url).query)
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return params["code"][0], params.get("state", [None])[0]
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async def main():
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"""Run the OAuth client example."""
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oauth_auth = OAuthClientProvider(
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server_url="http://localhost:8001",
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client_metadata=OAuthClientMetadata(
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client_name="Example MCP Client",
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redirect_uris=[AnyUrl("http://localhost:3000/callback")],
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grant_types=["authorization_code", "refresh_token"],
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response_types=["code"],
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scope="user",
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),
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storage=InMemoryTokenStorage(),
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redirect_handler=handle_redirect,
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callback_handler=handle_callback,
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)
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async with httpx.AsyncClient(auth=oauth_auth, follow_redirects=True) as custom_client:
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async with streamable_http_client("http://localhost:8001/mcp", http_client=custom_client) as (read, write, _):
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async with ClientSession(read, write) as session:
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await session.initialize()
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tools = await session.list_tools()
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print(f"Available tools: {[tool.name for tool in tools.tools]}")
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resources = await session.list_resources()
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print(f"Available resources: {[r.uri for r in resources.resources]}")
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def run():
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asyncio.run(main())
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if __name__ == "__main__":
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run()
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```
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_Full example: [examples/snippets/clients/oauth_client.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/clients/oauth_client.py)_
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<!-- /snippet-source -->
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For a complete working example, see [`examples/clients/simple-auth-client/`](../examples/clients/simple-auth-client/).
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For OAuth 2.1 client authentication, see [Authorization](authorization.md#client-side-authentication).
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## Roots
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@ -324,14 +226,12 @@ For a complete working example, see [`examples/clients/simple-auth-client/`](../
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Clients can provide a `list_roots_callback` so that servers can discover the client's workspace roots (directories, project folders, etc.):
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```python
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from typing import Any
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from mcp import ClientSession, types
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from mcp.shared.context import RequestContext
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async def handle_list_roots(
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context: RequestContext[ClientSession, Any],
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context: RequestContext[ClientSession, None],
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) -> types.ListRootsResult:
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"""Return the client's workspace roots."""
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return types.ListRootsResult(
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@ -384,7 +284,7 @@ async def main():
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asyncio.run(main())
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```
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The `sse_client()` function accepts optional `headers`, `timeout`, `sse_read_timeout`, and `auth` parameters. The SSE transport is considered legacy; prefer [Streamable HTTP](https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http) for new servers.
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The `sse_client()` function accepts optional `headers`, `timeout`, `sse_read_timeout`, and `auth` parameters. The SSE transport is considered legacy; prefer [Streamable HTTP](https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http) for new servers.
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## Ping
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@ -1,13 +0,0 @@
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# Concepts
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!!! warning "Under Construction"
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This page is currently being written. Check back soon for complete documentation.
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<!--
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- Server vs Client
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- Three primitives (tools, resources, prompts)
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- Transports (stdio, SSE, streamable HTTP)
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- Context and sessions
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- Lifecycle and state
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-->
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@ -58,12 +58,11 @@ npx -y @modelcontextprotocol/inspector
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<!-- TODO(Marcelo): automatically generate the follow references with a header on each of those files. -->
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1. **[Install](installation.md)** the MCP SDK
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2. **[Learn concepts](concepts.md)** - understand the three primitives and architecture
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3. **[Build servers](server.md)** - tools, resources, prompts, transports, ASGI mounting
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4. **[Write clients](client.md)** - connect to servers, use tools/resources/prompts
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5. **[Explore authorization](authorization.md)** - add security to your servers
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6. **[Use low-level APIs](low-level-server.md)** - for advanced customization
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7. **[Protocol features](protocol.md)** - MCP primitives, server capabilities
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2. **[Build servers](server.md)** - tools, resources, prompts, transports, ASGI mounting
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3. **[Write clients](client.md)** - connect to servers, use tools/resources/prompts
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4. **[Explore authorization](authorization.md)** - add security to your servers
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5. **[Use low-level APIs](low-level-server.md)** - for advanced customization
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6. **[Protocol features](protocol.md)** - MCP primitives, server capabilities
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## API Reference
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@ -1,5 +1,490 @@
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# Low-Level Server
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!!! warning "Under Construction"
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For more control, you can use the low-level server implementation directly. This gives you full access to the protocol and allows you to customize every aspect of your server, including lifecycle management through the lifespan API.
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This page is currently being written. Check back soon for complete documentation.
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## Lifespan
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<!-- snippet-source examples/snippets/servers/lowlevel/lifespan.py -->
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```python
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"""
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Run from the repository root:
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uv run examples/snippets/servers/lowlevel/lifespan.py
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"""
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from collections.abc import AsyncIterator
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from contextlib import asynccontextmanager
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from typing import Any
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import mcp.server.stdio
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import mcp.types as types
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from mcp.server.lowlevel import NotificationOptions, Server
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from mcp.server.models import InitializationOptions
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# Mock database class for example
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class Database:
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"""Mock database class for example."""
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@classmethod
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async def connect(cls) -> "Database":
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"""Connect to database."""
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print("Database connected")
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return cls()
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async def disconnect(self) -> None:
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"""Disconnect from database."""
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print("Database disconnected")
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async def query(self, query_str: str) -> list[dict[str, str]]:
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"""Execute a query."""
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# Simulate database query
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return [{"id": "1", "name": "Example", "query": query_str}]
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@asynccontextmanager
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async def server_lifespan(_server: Server) -> AsyncIterator[dict[str, Any]]:
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"""Manage server startup and shutdown lifecycle."""
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# Initialize resources on startup
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db = await Database.connect()
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try:
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yield {"db": db}
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finally:
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# Clean up on shutdown
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await db.disconnect()
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# Pass lifespan to server
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server = Server("example-server", lifespan=server_lifespan)
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@server.list_tools()
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async def handle_list_tools() -> list[types.Tool]:
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"""List available tools."""
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return [
|
||||
types.Tool(
|
||||
name="query_db",
|
||||
description="Query the database",
|
||||
inputSchema={
|
||||
"type": "object",
|
||||
"properties": {"query": {"type": "string", "description": "SQL query to execute"}},
|
||||
"required": ["query"],
|
||||
},
|
||||
)
|
||||
]
|
||||
|
||||
|
||||
@server.call_tool()
|
||||
async def query_db(name: str, arguments: dict[str, Any]) -> list[types.TextContent]:
|
||||
"""Handle database query tool call."""
|
||||
if name != "query_db":
|
||||
raise ValueError(f"Unknown tool: {name}")
|
||||
|
||||
# Access lifespan context
|
||||
ctx = server.request_context
|
||||
db = ctx.lifespan_context["db"]
|
||||
|
||||
# Execute query
|
||||
results = await db.query(arguments["query"])
|
||||
|
||||
return [types.TextContent(type="text", text=f"Query results: {results}")]
|
||||
|
||||
|
||||
async def run():
|
||||
"""Run the server with lifespan management."""
|
||||
async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
|
||||
await server.run(
|
||||
read_stream,
|
||||
write_stream,
|
||||
InitializationOptions(
|
||||
server_name="example-server",
|
||||
server_version="0.1.0",
|
||||
capabilities=server.get_capabilities(
|
||||
notification_options=NotificationOptions(),
|
||||
experimental_capabilities={},
|
||||
),
|
||||
),
|
||||
)
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
import asyncio
|
||||
|
||||
asyncio.run(run())
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/servers/lowlevel/lifespan.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/lowlevel/lifespan.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
The lifespan API provides:
|
||||
|
||||
- A way to initialize resources when the server starts and clean them up when it stops
|
||||
- Access to initialized resources through the request context in handlers
|
||||
- Type-safe context passing between lifespan and request handlers
|
||||
|
||||
## Basic Example
|
||||
|
||||
<!-- snippet-source examples/snippets/servers/lowlevel/basic.py -->
|
||||
```python
|
||||
"""
|
||||
Run from the repository root:
|
||||
uv run examples/snippets/servers/lowlevel/basic.py
|
||||
"""
|
||||
|
||||
import asyncio
|
||||
|
||||
import mcp.server.stdio
|
||||
import mcp.types as types
|
||||
from mcp.server.lowlevel import NotificationOptions, Server
|
||||
from mcp.server.models import InitializationOptions
|
||||
|
||||
# Create a server instance
|
||||
server = Server("example-server")
|
||||
|
||||
|
||||
@server.list_prompts()
|
||||
async def handle_list_prompts() -> list[types.Prompt]:
|
||||
"""List available prompts."""
|
||||
return [
|
||||
types.Prompt(
|
||||
name="example-prompt",
|
||||
description="An example prompt template",
|
||||
arguments=[types.PromptArgument(name="arg1", description="Example argument", required=True)],
|
||||
)
|
||||
]
|
||||
|
||||
|
||||
@server.get_prompt()
|
||||
async def handle_get_prompt(name: str, arguments: dict[str, str] | None) -> types.GetPromptResult:
|
||||
"""Get a specific prompt by name."""
|
||||
if name != "example-prompt":
|
||||
raise ValueError(f"Unknown prompt: {name}")
|
||||
|
||||
arg1_value = (arguments or {}).get("arg1", "default")
|
||||
|
||||
return types.GetPromptResult(
|
||||
description="Example prompt",
|
||||
messages=[
|
||||
types.PromptMessage(
|
||||
role="user",
|
||||
content=types.TextContent(type="text", text=f"Example prompt text with argument: {arg1_value}"),
|
||||
)
|
||||
],
|
||||
)
|
||||
|
||||
|
||||
async def run():
|
||||
"""Run the basic low-level server."""
|
||||
async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
|
||||
await server.run(
|
||||
read_stream,
|
||||
write_stream,
|
||||
InitializationOptions(
|
||||
server_name="example",
|
||||
server_version="0.1.0",
|
||||
capabilities=server.get_capabilities(
|
||||
notification_options=NotificationOptions(),
|
||||
experimental_capabilities={},
|
||||
),
|
||||
),
|
||||
)
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
asyncio.run(run())
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/servers/lowlevel/basic.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/lowlevel/basic.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
Caution: The `uv run mcp run` and `uv run mcp dev` tool doesn't support low-level server.
|
||||
|
||||
## Structured Output Support
|
||||
|
||||
The low-level server supports structured output for tools, allowing you to return both human-readable content and machine-readable structured data. Tools can define an `outputSchema` to validate their structured output:
|
||||
|
||||
<!-- snippet-source examples/snippets/servers/lowlevel/structured_output.py -->
|
||||
```python
|
||||
"""
|
||||
Run from the repository root:
|
||||
uv run examples/snippets/servers/lowlevel/structured_output.py
|
||||
"""
|
||||
|
||||
import asyncio
|
||||
from typing import Any
|
||||
|
||||
import mcp.server.stdio
|
||||
import mcp.types as types
|
||||
from mcp.server.lowlevel import NotificationOptions, Server
|
||||
from mcp.server.models import InitializationOptions
|
||||
|
||||
server = Server("example-server")
|
||||
|
||||
|
||||
@server.list_tools()
|
||||
async def list_tools() -> list[types.Tool]:
|
||||
"""List available tools with structured output schemas."""
|
||||
return [
|
||||
types.Tool(
|
||||
name="get_weather",
|
||||
description="Get current weather for a city",
|
||||
inputSchema={
|
||||
"type": "object",
|
||||
"properties": {"city": {"type": "string", "description": "City name"}},
|
||||
"required": ["city"],
|
||||
},
|
||||
outputSchema={
|
||||
"type": "object",
|
||||
"properties": {
|
||||
"temperature": {"type": "number", "description": "Temperature in Celsius"},
|
||||
"condition": {"type": "string", "description": "Weather condition"},
|
||||
"humidity": {"type": "number", "description": "Humidity percentage"},
|
||||
"city": {"type": "string", "description": "City name"},
|
||||
},
|
||||
"required": ["temperature", "condition", "humidity", "city"],
|
||||
},
|
||||
)
|
||||
]
|
||||
|
||||
|
||||
@server.call_tool()
|
||||
async def call_tool(name: str, arguments: dict[str, Any]) -> dict[str, Any]:
|
||||
"""Handle tool calls with structured output."""
|
||||
if name == "get_weather":
|
||||
city = arguments["city"]
|
||||
|
||||
# Simulated weather data - in production, call a weather API
|
||||
weather_data = {
|
||||
"temperature": 22.5,
|
||||
"condition": "partly cloudy",
|
||||
"humidity": 65,
|
||||
"city": city, # Include the requested city
|
||||
}
|
||||
|
||||
# low-level server will validate structured output against the tool's
|
||||
# output schema, and additionally serialize it into a TextContent block
|
||||
# for backwards compatibility with pre-2025-06-18 clients.
|
||||
return weather_data
|
||||
else:
|
||||
raise ValueError(f"Unknown tool: {name}")
|
||||
|
||||
|
||||
async def run():
|
||||
"""Run the structured output server."""
|
||||
async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
|
||||
await server.run(
|
||||
read_stream,
|
||||
write_stream,
|
||||
InitializationOptions(
|
||||
server_name="structured-output-example",
|
||||
server_version="0.1.0",
|
||||
capabilities=server.get_capabilities(
|
||||
notification_options=NotificationOptions(),
|
||||
experimental_capabilities={},
|
||||
),
|
||||
),
|
||||
)
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
asyncio.run(run())
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/servers/lowlevel/structured_output.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/lowlevel/structured_output.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
Tools can return data in four ways:
|
||||
|
||||
1. **Content only**: Return a list of content blocks (default behavior before spec revision 2025-06-18)
|
||||
2. **Structured data only**: Return a dictionary that will be serialized to JSON (Introduced in spec revision 2025-06-18)
|
||||
3. **Both**: Return a tuple of (content, structured_data) preferred option to use for backwards compatibility
|
||||
4. **Direct CallToolResult**: Return `CallToolResult` directly for full control (including `_meta` field)
|
||||
|
||||
When an `outputSchema` is defined, the server automatically validates the structured output against the schema. This ensures type safety and helps catch errors early.
|
||||
|
||||
### Returning CallToolResult Directly
|
||||
|
||||
For full control over the response including the `_meta` field (for passing data to client applications without exposing it to the model), return `CallToolResult` directly:
|
||||
|
||||
<!-- snippet-source examples/snippets/servers/lowlevel/direct_call_tool_result.py -->
|
||||
```python
|
||||
"""
|
||||
Run from the repository root:
|
||||
uv run examples/snippets/servers/lowlevel/direct_call_tool_result.py
|
||||
"""
|
||||
|
||||
import asyncio
|
||||
from typing import Any
|
||||
|
||||
import mcp.server.stdio
|
||||
import mcp.types as types
|
||||
from mcp.server.lowlevel import NotificationOptions, Server
|
||||
from mcp.server.models import InitializationOptions
|
||||
|
||||
server = Server("example-server")
|
||||
|
||||
|
||||
@server.list_tools()
|
||||
async def list_tools() -> list[types.Tool]:
|
||||
"""List available tools."""
|
||||
return [
|
||||
types.Tool(
|
||||
name="advanced_tool",
|
||||
description="Tool with full control including _meta field",
|
||||
inputSchema={
|
||||
"type": "object",
|
||||
"properties": {"message": {"type": "string"}},
|
||||
"required": ["message"],
|
||||
},
|
||||
)
|
||||
]
|
||||
|
||||
|
||||
@server.call_tool()
|
||||
async def handle_call_tool(name: str, arguments: dict[str, Any]) -> types.CallToolResult:
|
||||
"""Handle tool calls by returning CallToolResult directly."""
|
||||
if name == "advanced_tool":
|
||||
message = str(arguments.get("message", ""))
|
||||
return types.CallToolResult(
|
||||
content=[types.TextContent(type="text", text=f"Processed: {message}")],
|
||||
structuredContent={"result": "success", "message": message},
|
||||
_meta={"hidden": "data for client applications only"},
|
||||
)
|
||||
|
||||
raise ValueError(f"Unknown tool: {name}")
|
||||
|
||||
|
||||
async def run():
|
||||
"""Run the server."""
|
||||
async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
|
||||
await server.run(
|
||||
read_stream,
|
||||
write_stream,
|
||||
InitializationOptions(
|
||||
server_name="example",
|
||||
server_version="0.1.0",
|
||||
capabilities=server.get_capabilities(
|
||||
notification_options=NotificationOptions(),
|
||||
experimental_capabilities={},
|
||||
),
|
||||
),
|
||||
)
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
asyncio.run(run())
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/servers/lowlevel/direct_call_tool_result.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/lowlevel/direct_call_tool_result.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
**Note:** When returning `CallToolResult`, you bypass the automatic content/structured conversion. You must construct the complete response yourself.
|
||||
|
||||
## Pagination (Advanced)
|
||||
|
||||
For servers that need to handle large datasets, the low-level server provides paginated versions of list operations. This is an optional optimization - most servers won't need pagination unless they're dealing with hundreds or thousands of items.
|
||||
|
||||
### Server-side Implementation
|
||||
|
||||
<!-- snippet-source examples/snippets/servers/pagination_example.py -->
|
||||
```python
|
||||
"""
|
||||
Example of implementing pagination with MCP server decorators.
|
||||
"""
|
||||
|
||||
from pydantic import AnyUrl
|
||||
|
||||
import mcp.types as types
|
||||
from mcp.server.lowlevel import Server
|
||||
|
||||
# Initialize the server
|
||||
server = Server("paginated-server")
|
||||
|
||||
# Sample data to paginate
|
||||
ITEMS = [f"Item {i}" for i in range(1, 101)] # 100 items
|
||||
|
||||
|
||||
@server.list_resources()
|
||||
async def list_resources_paginated(request: types.ListResourcesRequest) -> types.ListResourcesResult:
|
||||
"""List resources with pagination support."""
|
||||
page_size = 10
|
||||
|
||||
# Extract cursor from request params
|
||||
cursor = request.params.cursor if request.params is not None else None
|
||||
|
||||
# Parse cursor to get offset
|
||||
start = 0 if cursor is None else int(cursor)
|
||||
end = start + page_size
|
||||
|
||||
# Get page of resources
|
||||
page_items = [
|
||||
types.Resource(uri=AnyUrl(f"resource://items/{item}"), name=item, description=f"Description for {item}")
|
||||
for item in ITEMS[start:end]
|
||||
]
|
||||
|
||||
# Determine next cursor
|
||||
next_cursor = str(end) if end < len(ITEMS) else None
|
||||
|
||||
return types.ListResourcesResult(resources=page_items, nextCursor=next_cursor)
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/servers/pagination_example.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/pagination_example.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
### Client-side Consumption
|
||||
|
||||
<!-- snippet-source examples/snippets/clients/pagination_client.py -->
|
||||
```python
|
||||
"""
|
||||
Example of consuming paginated MCP endpoints from a client.
|
||||
"""
|
||||
|
||||
import asyncio
|
||||
|
||||
from mcp.client.session import ClientSession
|
||||
from mcp.client.stdio import StdioServerParameters, stdio_client
|
||||
from mcp.types import PaginatedRequestParams, Resource
|
||||
|
||||
|
||||
async def list_all_resources() -> None:
|
||||
"""Fetch all resources using pagination."""
|
||||
async with stdio_client(StdioServerParameters(command="uv", args=["run", "mcp-simple-pagination"])) as (
|
||||
read,
|
||||
write,
|
||||
):
|
||||
async with ClientSession(read, write) as session:
|
||||
await session.initialize()
|
||||
|
||||
all_resources: list[Resource] = []
|
||||
cursor = None
|
||||
|
||||
while True:
|
||||
# Fetch a page of resources
|
||||
result = await session.list_resources(params=PaginatedRequestParams(cursor=cursor))
|
||||
all_resources.extend(result.resources)
|
||||
|
||||
print(f"Fetched {len(result.resources)} resources")
|
||||
|
||||
# Check if there are more pages
|
||||
if result.nextCursor:
|
||||
cursor = result.nextCursor
|
||||
else:
|
||||
break
|
||||
|
||||
print(f"Total resources: {len(all_resources)}")
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
asyncio.run(list_all_resources())
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/clients/pagination_client.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/clients/pagination_client.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
### Key Points
|
||||
|
||||
- **Cursors are opaque strings** - the server defines the format (numeric offsets, timestamps, etc.)
|
||||
- **Return `nextCursor=None`** when there are no more pages
|
||||
- **Backward compatible** - clients that don't support pagination will still work (they'll just get the first page)
|
||||
- **Flexible page sizes** - Each endpoint can define its own page size based on data characteristics
|
||||
|
||||
See the [simple-pagination example](examples/servers/simple-pagination) for a complete implementation.
|
||||
|
|
|
|||
|
|
@ -138,5 +138,5 @@ For FastMCP tools, input schemas are derived automatically from function signatu
|
|||
|
||||
For pagination details, see:
|
||||
|
||||
- Server-side implementation: [Building Servers - Pagination](server.md#pagination-advanced)
|
||||
- Client-side consumption: [Building Servers - Client-side Consumption](server.md#client-side-consumption)
|
||||
- Server-side implementation: [Low-Level Server - Pagination](low-level-server.md#pagination-advanced)
|
||||
- Client-side consumption: [Low-Level Server - Client-side Consumption](low-level-server.md#client-side-consumption)
|
||||
|
|
|
|||
610
docs/server.md
610
docs/server.md
|
|
@ -554,7 +554,7 @@ from mcp.server.fastmcp import FastMCP, Icon
|
|||
icon = Icon(
|
||||
src="icon.png",
|
||||
mimeType="image/png",
|
||||
sizes="64x64"
|
||||
sizes=["64x64"]
|
||||
)
|
||||
|
||||
# Add icons to server
|
||||
|
|
@ -576,7 +576,7 @@ def my_resource():
|
|||
return "content"
|
||||
```
|
||||
|
||||
_Full example: [examples/fastmcp/icons_demo.py](https://github.com/modelcontextprotocol/python-sdk/blob/v1.x/examples/fastmcp/icons_demo.py)_
|
||||
_Full example: [examples/fastmcp/icons_demo.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/fastmcp/icons_demo.py)_
|
||||
|
||||
### Images
|
||||
|
||||
|
|
@ -973,7 +973,6 @@ The `elicit()` method returns an `ElicitationResult` with:
|
|||
|
||||
- `action`: "accept", "decline", or "cancel"
|
||||
- `data`: The validated response (only when accepted)
|
||||
- `validation_error`: Any validation error message
|
||||
|
||||
#### Elicitation with Enum Values
|
||||
|
||||
|
|
@ -1007,50 +1006,28 @@ async def pick_color(ctx: Context[ServerSession, None]) -> str:
|
|||
return "No color selected"
|
||||
```
|
||||
|
||||
#### URL Mode Elicitation
|
||||
#### Elicitation Complete Notification
|
||||
|
||||
URL mode elicitation directs the user to an external URL for out-of-band interactions — for example, entering sensitive data that should not pass through the LLM, or filling out a complex form like a shipping address. The tool call blocks while waiting for the user to complete the interaction:
|
||||
For URL mode elicitations, send a completion notification after the out-of-band interaction finishes. This tells the client that the elicitation is done and it may retry any blocked requests:
|
||||
|
||||
```python
|
||||
import asyncio
|
||||
import uuid
|
||||
|
||||
import anyio
|
||||
|
||||
from mcp.server.fastmcp import Context, FastMCP
|
||||
from mcp.server.session import ServerSession
|
||||
|
||||
mcp = FastMCP("Shipping Example")
|
||||
|
||||
# Simulates a database that the web form writes to on submit
|
||||
completed_elicitations: dict[str, dict] = {}
|
||||
mcp = FastMCP("Elicit Complete Example")
|
||||
|
||||
|
||||
@mcp.tool()
|
||||
async def place_order(item: str, ctx: Context[ServerSession, None]) -> str:
|
||||
"""Place an order (shipping details collected via secure form)."""
|
||||
elicitation_id = str(uuid.uuid4())
|
||||
async def handle_oauth_callback(
|
||||
elicitation_id: str, ctx: Context[ServerSession, None]
|
||||
) -> str:
|
||||
"""Called when OAuth flow completes out-of-band."""
|
||||
# ... process the callback ...
|
||||
|
||||
# Direct the user to a form to enter their shipping address
|
||||
result = await ctx.elicit_url(
|
||||
message=f"Please enter your shipping details for '{item}'.",
|
||||
url=f"https://example.com/shipping?id={elicitation_id}",
|
||||
elicitation_id=elicitation_id,
|
||||
)
|
||||
|
||||
if result.action != "accept":
|
||||
return "Order cancelled."
|
||||
|
||||
# Poll until the shipping form is submitted
|
||||
with anyio.fail_after(120):
|
||||
while elicitation_id not in completed_elicitations:
|
||||
await asyncio.sleep(1)
|
||||
|
||||
# Notify the client that the out-of-band interaction is done
|
||||
# Notify the client that the elicitation is done
|
||||
await ctx.session.send_elicit_complete(elicitation_id)
|
||||
|
||||
shipping = completed_elicitations.pop(elicitation_id)
|
||||
return f"Order placed! Shipping '{item}' to {shipping['address']}"
|
||||
return "Authorization complete"
|
||||
```
|
||||
|
||||
### Sampling
|
||||
|
|
@ -1144,75 +1121,7 @@ When this handler is registered, the server automatically declares the `logging`
|
|||
|
||||
### Authentication
|
||||
|
||||
Authentication can be used by servers that want to expose tools accessing protected resources.
|
||||
|
||||
`mcp.server.auth` implements OAuth 2.1 resource server functionality, where MCP servers act as Resource Servers (RS) that validate tokens issued by separate Authorization Servers (AS). This follows the [MCP authorization specification](https://modelcontextprotocol.io/specification/2025-06-18/basic/authorization) and implements RFC 9728 (Protected Resource Metadata) for AS discovery.
|
||||
|
||||
MCP servers can use authentication by providing an implementation of the `TokenVerifier` protocol:
|
||||
|
||||
<!-- snippet-source examples/snippets/servers/oauth_server.py -->
|
||||
```python
|
||||
"""
|
||||
Run from the repository root:
|
||||
uv run examples/snippets/servers/oauth_server.py
|
||||
"""
|
||||
|
||||
from pydantic import AnyHttpUrl
|
||||
|
||||
from mcp.server.auth.provider import AccessToken, TokenVerifier
|
||||
from mcp.server.auth.settings import AuthSettings
|
||||
from mcp.server.fastmcp import FastMCP
|
||||
|
||||
|
||||
class SimpleTokenVerifier(TokenVerifier):
|
||||
"""Simple token verifier for demonstration."""
|
||||
|
||||
async def verify_token(self, token: str) -> AccessToken | None:
|
||||
pass # This is where you would implement actual token validation
|
||||
|
||||
|
||||
# Create FastMCP instance as a Resource Server
|
||||
mcp = FastMCP(
|
||||
"Weather Service",
|
||||
json_response=True,
|
||||
# Token verifier for authentication
|
||||
token_verifier=SimpleTokenVerifier(),
|
||||
# Auth settings for RFC 9728 Protected Resource Metadata
|
||||
auth=AuthSettings(
|
||||
issuer_url=AnyHttpUrl("https://auth.example.com"), # Authorization Server URL
|
||||
resource_server_url=AnyHttpUrl("http://localhost:3001"), # This server's URL
|
||||
required_scopes=["user"],
|
||||
),
|
||||
)
|
||||
|
||||
|
||||
@mcp.tool()
|
||||
async def get_weather(city: str = "London") -> dict[str, str]:
|
||||
"""Get weather data for a city"""
|
||||
return {
|
||||
"city": city,
|
||||
"temperature": "22",
|
||||
"condition": "Partly cloudy",
|
||||
"humidity": "65%",
|
||||
}
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
mcp.run(transport="streamable-http")
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/servers/oauth_server.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/oauth_server.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
For a complete example with separate Authorization Server and Resource Server implementations, see [`examples/servers/simple-auth/`](../examples/servers/simple-auth/).
|
||||
|
||||
**Architecture:**
|
||||
|
||||
- **Authorization Server (AS)**: Handles OAuth flows, user authentication, and token issuance
|
||||
- **Resource Server (RS)**: Your MCP server that validates tokens and serves protected resources
|
||||
- **Client**: Discovers AS through RFC 9728, obtains tokens, and uses them with the MCP server
|
||||
|
||||
See [TokenVerifier](../src/mcp/server/auth/provider.py) for more details on implementing token validation.
|
||||
For OAuth 2.1 server and client authentication, see [Authorization](authorization.md).
|
||||
|
||||
### FastMCP Properties
|
||||
|
||||
|
|
@ -1492,8 +1401,8 @@ _Full example: [examples/snippets/servers/streamable_starlette_mount.py](https:/
|
|||
|
||||
For low level server with Streamable HTTP implementations, see:
|
||||
|
||||
- Stateful server: [`examples/servers/simple-streamablehttp/`](../examples/servers/simple-streamablehttp/)
|
||||
- Stateless server: [`examples/servers/simple-streamablehttp-stateless/`](../examples/servers/simple-streamablehttp-stateless/)
|
||||
- Stateful server: [`examples/servers/simple-streamablehttp/`](examples/servers/simple-streamablehttp/)
|
||||
- Stateless server: [`examples/servers/simple-streamablehttp-stateless/`](examples/servers/simple-streamablehttp-stateless/)
|
||||
|
||||
The streamable HTTP transport supports:
|
||||
|
||||
|
|
@ -1739,7 +1648,7 @@ _Full example: [examples/snippets/servers/streamable_http_path_config.py](https:
|
|||
|
||||
#### SSE servers
|
||||
|
||||
> **Note**: SSE transport is being superseded by [Streamable HTTP transport](https://modelcontextprotocol.io/specification/2025-03-26/basic/transports#streamable-http).
|
||||
> **Note**: SSE transport is being superseded by [Streamable HTTP transport](https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#streamable-http).
|
||||
|
||||
You can mount the SSE server to an existing ASGI server using the `sse_app` method. This allows you to integrate the SSE server with other ASGI applications.
|
||||
|
||||
|
|
@ -1803,489 +1712,4 @@ For more information on mounting applications in Starlette, see the [Starlette d
|
|||
|
||||
## Advanced Usage
|
||||
|
||||
### Low-Level Server
|
||||
|
||||
For more control, you can use the low-level server implementation directly. This gives you full access to the protocol and allows you to customize every aspect of your server, including lifecycle management through the lifespan API:
|
||||
|
||||
<!-- snippet-source examples/snippets/servers/lowlevel/lifespan.py -->
|
||||
```python
|
||||
"""
|
||||
Run from the repository root:
|
||||
uv run examples/snippets/servers/lowlevel/lifespan.py
|
||||
"""
|
||||
|
||||
from collections.abc import AsyncIterator
|
||||
from contextlib import asynccontextmanager
|
||||
from typing import Any
|
||||
|
||||
import mcp.server.stdio
|
||||
import mcp.types as types
|
||||
from mcp.server.lowlevel import NotificationOptions, Server
|
||||
from mcp.server.models import InitializationOptions
|
||||
|
||||
|
||||
# Mock database class for example
|
||||
class Database:
|
||||
"""Mock database class for example."""
|
||||
|
||||
@classmethod
|
||||
async def connect(cls) -> "Database":
|
||||
"""Connect to database."""
|
||||
print("Database connected")
|
||||
return cls()
|
||||
|
||||
async def disconnect(self) -> None:
|
||||
"""Disconnect from database."""
|
||||
print("Database disconnected")
|
||||
|
||||
async def query(self, query_str: str) -> list[dict[str, str]]:
|
||||
"""Execute a query."""
|
||||
# Simulate database query
|
||||
return [{"id": "1", "name": "Example", "query": query_str}]
|
||||
|
||||
|
||||
@asynccontextmanager
|
||||
async def server_lifespan(_server: Server) -> AsyncIterator[dict[str, Any]]:
|
||||
"""Manage server startup and shutdown lifecycle."""
|
||||
# Initialize resources on startup
|
||||
db = await Database.connect()
|
||||
try:
|
||||
yield {"db": db}
|
||||
finally:
|
||||
# Clean up on shutdown
|
||||
await db.disconnect()
|
||||
|
||||
|
||||
# Pass lifespan to server
|
||||
server = Server("example-server", lifespan=server_lifespan)
|
||||
|
||||
|
||||
@server.list_tools()
|
||||
async def handle_list_tools() -> list[types.Tool]:
|
||||
"""List available tools."""
|
||||
return [
|
||||
types.Tool(
|
||||
name="query_db",
|
||||
description="Query the database",
|
||||
inputSchema={
|
||||
"type": "object",
|
||||
"properties": {"query": {"type": "string", "description": "SQL query to execute"}},
|
||||
"required": ["query"],
|
||||
},
|
||||
)
|
||||
]
|
||||
|
||||
|
||||
@server.call_tool()
|
||||
async def query_db(name: str, arguments: dict[str, Any]) -> list[types.TextContent]:
|
||||
"""Handle database query tool call."""
|
||||
if name != "query_db":
|
||||
raise ValueError(f"Unknown tool: {name}")
|
||||
|
||||
# Access lifespan context
|
||||
ctx = server.request_context
|
||||
db = ctx.lifespan_context["db"]
|
||||
|
||||
# Execute query
|
||||
results = await db.query(arguments["query"])
|
||||
|
||||
return [types.TextContent(type="text", text=f"Query results: {results}")]
|
||||
|
||||
|
||||
async def run():
|
||||
"""Run the server with lifespan management."""
|
||||
async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
|
||||
await server.run(
|
||||
read_stream,
|
||||
write_stream,
|
||||
InitializationOptions(
|
||||
server_name="example-server",
|
||||
server_version="0.1.0",
|
||||
capabilities=server.get_capabilities(
|
||||
notification_options=NotificationOptions(),
|
||||
experimental_capabilities={},
|
||||
),
|
||||
),
|
||||
)
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
import asyncio
|
||||
|
||||
asyncio.run(run())
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/servers/lowlevel/lifespan.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/lowlevel/lifespan.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
The lifespan API provides:
|
||||
|
||||
- A way to initialize resources when the server starts and clean them up when it stops
|
||||
- Access to initialized resources through the request context in handlers
|
||||
- Type-safe context passing between lifespan and request handlers
|
||||
|
||||
<!-- snippet-source examples/snippets/servers/lowlevel/basic.py -->
|
||||
```python
|
||||
"""
|
||||
Run from the repository root:
|
||||
uv run examples/snippets/servers/lowlevel/basic.py
|
||||
"""
|
||||
|
||||
import asyncio
|
||||
|
||||
import mcp.server.stdio
|
||||
import mcp.types as types
|
||||
from mcp.server.lowlevel import NotificationOptions, Server
|
||||
from mcp.server.models import InitializationOptions
|
||||
|
||||
# Create a server instance
|
||||
server = Server("example-server")
|
||||
|
||||
|
||||
@server.list_prompts()
|
||||
async def handle_list_prompts() -> list[types.Prompt]:
|
||||
"""List available prompts."""
|
||||
return [
|
||||
types.Prompt(
|
||||
name="example-prompt",
|
||||
description="An example prompt template",
|
||||
arguments=[types.PromptArgument(name="arg1", description="Example argument", required=True)],
|
||||
)
|
||||
]
|
||||
|
||||
|
||||
@server.get_prompt()
|
||||
async def handle_get_prompt(name: str, arguments: dict[str, str] | None) -> types.GetPromptResult:
|
||||
"""Get a specific prompt by name."""
|
||||
if name != "example-prompt":
|
||||
raise ValueError(f"Unknown prompt: {name}")
|
||||
|
||||
arg1_value = (arguments or {}).get("arg1", "default")
|
||||
|
||||
return types.GetPromptResult(
|
||||
description="Example prompt",
|
||||
messages=[
|
||||
types.PromptMessage(
|
||||
role="user",
|
||||
content=types.TextContent(type="text", text=f"Example prompt text with argument: {arg1_value}"),
|
||||
)
|
||||
],
|
||||
)
|
||||
|
||||
|
||||
async def run():
|
||||
"""Run the basic low-level server."""
|
||||
async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
|
||||
await server.run(
|
||||
read_stream,
|
||||
write_stream,
|
||||
InitializationOptions(
|
||||
server_name="example",
|
||||
server_version="0.1.0",
|
||||
capabilities=server.get_capabilities(
|
||||
notification_options=NotificationOptions(),
|
||||
experimental_capabilities={},
|
||||
),
|
||||
),
|
||||
)
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
asyncio.run(run())
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/servers/lowlevel/basic.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/lowlevel/basic.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
Caution: The `uv run mcp run` and `uv run mcp dev` tool doesn't support low-level server.
|
||||
|
||||
#### Structured Output Support
|
||||
|
||||
The low-level server supports structured output for tools, allowing you to return both human-readable content and machine-readable structured data. Tools can define an `outputSchema` to validate their structured output:
|
||||
|
||||
<!-- snippet-source examples/snippets/servers/lowlevel/structured_output.py -->
|
||||
```python
|
||||
"""
|
||||
Run from the repository root:
|
||||
uv run examples/snippets/servers/lowlevel/structured_output.py
|
||||
"""
|
||||
|
||||
import asyncio
|
||||
from typing import Any
|
||||
|
||||
import mcp.server.stdio
|
||||
import mcp.types as types
|
||||
from mcp.server.lowlevel import NotificationOptions, Server
|
||||
from mcp.server.models import InitializationOptions
|
||||
|
||||
server = Server("example-server")
|
||||
|
||||
|
||||
@server.list_tools()
|
||||
async def list_tools() -> list[types.Tool]:
|
||||
"""List available tools with structured output schemas."""
|
||||
return [
|
||||
types.Tool(
|
||||
name="get_weather",
|
||||
description="Get current weather for a city",
|
||||
inputSchema={
|
||||
"type": "object",
|
||||
"properties": {"city": {"type": "string", "description": "City name"}},
|
||||
"required": ["city"],
|
||||
},
|
||||
outputSchema={
|
||||
"type": "object",
|
||||
"properties": {
|
||||
"temperature": {"type": "number", "description": "Temperature in Celsius"},
|
||||
"condition": {"type": "string", "description": "Weather condition"},
|
||||
"humidity": {"type": "number", "description": "Humidity percentage"},
|
||||
"city": {"type": "string", "description": "City name"},
|
||||
},
|
||||
"required": ["temperature", "condition", "humidity", "city"],
|
||||
},
|
||||
)
|
||||
]
|
||||
|
||||
|
||||
@server.call_tool()
|
||||
async def call_tool(name: str, arguments: dict[str, Any]) -> dict[str, Any]:
|
||||
"""Handle tool calls with structured output."""
|
||||
if name == "get_weather":
|
||||
city = arguments["city"]
|
||||
|
||||
# Simulated weather data - in production, call a weather API
|
||||
weather_data = {
|
||||
"temperature": 22.5,
|
||||
"condition": "partly cloudy",
|
||||
"humidity": 65,
|
||||
"city": city, # Include the requested city
|
||||
}
|
||||
|
||||
# low-level server will validate structured output against the tool's
|
||||
# output schema, and additionally serialize it into a TextContent block
|
||||
# for backwards compatibility with pre-2025-06-18 clients.
|
||||
return weather_data
|
||||
else:
|
||||
raise ValueError(f"Unknown tool: {name}")
|
||||
|
||||
|
||||
async def run():
|
||||
"""Run the structured output server."""
|
||||
async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
|
||||
await server.run(
|
||||
read_stream,
|
||||
write_stream,
|
||||
InitializationOptions(
|
||||
server_name="structured-output-example",
|
||||
server_version="0.1.0",
|
||||
capabilities=server.get_capabilities(
|
||||
notification_options=NotificationOptions(),
|
||||
experimental_capabilities={},
|
||||
),
|
||||
),
|
||||
)
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
asyncio.run(run())
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/servers/lowlevel/structured_output.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/lowlevel/structured_output.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
Tools can return data in four ways:
|
||||
|
||||
1. **Content only**: Return a list of content blocks (default behavior before spec revision 2025-06-18)
|
||||
2. **Structured data only**: Return a dictionary that will be serialized to JSON (Introduced in spec revision 2025-06-18)
|
||||
3. **Both**: Return a tuple of (content, structured_data) preferred option to use for backwards compatibility
|
||||
4. **Direct CallToolResult**: Return `CallToolResult` directly for full control (including `_meta` field)
|
||||
|
||||
When an `outputSchema` is defined, the server automatically validates the structured output against the schema. This ensures type safety and helps catch errors early.
|
||||
|
||||
##### Returning CallToolResult Directly
|
||||
|
||||
For full control over the response including the `_meta` field (for passing data to client applications without exposing it to the model), return `CallToolResult` directly:
|
||||
|
||||
<!-- snippet-source examples/snippets/servers/lowlevel/direct_call_tool_result.py -->
|
||||
```python
|
||||
"""
|
||||
Run from the repository root:
|
||||
uv run examples/snippets/servers/lowlevel/direct_call_tool_result.py
|
||||
"""
|
||||
|
||||
import asyncio
|
||||
from typing import Any
|
||||
|
||||
import mcp.server.stdio
|
||||
import mcp.types as types
|
||||
from mcp.server.lowlevel import NotificationOptions, Server
|
||||
from mcp.server.models import InitializationOptions
|
||||
|
||||
server = Server("example-server")
|
||||
|
||||
|
||||
@server.list_tools()
|
||||
async def list_tools() -> list[types.Tool]:
|
||||
"""List available tools."""
|
||||
return [
|
||||
types.Tool(
|
||||
name="advanced_tool",
|
||||
description="Tool with full control including _meta field",
|
||||
inputSchema={
|
||||
"type": "object",
|
||||
"properties": {"message": {"type": "string"}},
|
||||
"required": ["message"],
|
||||
},
|
||||
)
|
||||
]
|
||||
|
||||
|
||||
@server.call_tool()
|
||||
async def handle_call_tool(name: str, arguments: dict[str, Any]) -> types.CallToolResult:
|
||||
"""Handle tool calls by returning CallToolResult directly."""
|
||||
if name == "advanced_tool":
|
||||
message = str(arguments.get("message", ""))
|
||||
return types.CallToolResult(
|
||||
content=[types.TextContent(type="text", text=f"Processed: {message}")],
|
||||
structuredContent={"result": "success", "message": message},
|
||||
_meta={"hidden": "data for client applications only"},
|
||||
)
|
||||
|
||||
raise ValueError(f"Unknown tool: {name}")
|
||||
|
||||
|
||||
async def run():
|
||||
"""Run the server."""
|
||||
async with mcp.server.stdio.stdio_server() as (read_stream, write_stream):
|
||||
await server.run(
|
||||
read_stream,
|
||||
write_stream,
|
||||
InitializationOptions(
|
||||
server_name="example",
|
||||
server_version="0.1.0",
|
||||
capabilities=server.get_capabilities(
|
||||
notification_options=NotificationOptions(),
|
||||
experimental_capabilities={},
|
||||
),
|
||||
),
|
||||
)
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
asyncio.run(run())
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/servers/lowlevel/direct_call_tool_result.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/lowlevel/direct_call_tool_result.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
**Note:** When returning `CallToolResult`, you bypass the automatic content/structured conversion. You must construct the complete response yourself.
|
||||
|
||||
### Pagination (Advanced)
|
||||
|
||||
For servers that need to handle large datasets, the low-level server provides paginated versions of list operations. This is an optional optimization - most servers won't need pagination unless they're dealing with hundreds or thousands of items.
|
||||
|
||||
#### Server-side Implementation
|
||||
|
||||
<!-- snippet-source examples/snippets/servers/pagination_example.py -->
|
||||
```python
|
||||
"""
|
||||
Example of implementing pagination with MCP server decorators.
|
||||
"""
|
||||
|
||||
from pydantic import AnyUrl
|
||||
|
||||
import mcp.types as types
|
||||
from mcp.server.lowlevel import Server
|
||||
|
||||
# Initialize the server
|
||||
server = Server("paginated-server")
|
||||
|
||||
# Sample data to paginate
|
||||
ITEMS = [f"Item {i}" for i in range(1, 101)] # 100 items
|
||||
|
||||
|
||||
@server.list_resources()
|
||||
async def list_resources_paginated(request: types.ListResourcesRequest) -> types.ListResourcesResult:
|
||||
"""List resources with pagination support."""
|
||||
page_size = 10
|
||||
|
||||
# Extract cursor from request params
|
||||
cursor = request.params.cursor if request.params is not None else None
|
||||
|
||||
# Parse cursor to get offset
|
||||
start = 0 if cursor is None else int(cursor)
|
||||
end = start + page_size
|
||||
|
||||
# Get page of resources
|
||||
page_items = [
|
||||
types.Resource(uri=AnyUrl(f"resource://items/{item}"), name=item, description=f"Description for {item}")
|
||||
for item in ITEMS[start:end]
|
||||
]
|
||||
|
||||
# Determine next cursor
|
||||
next_cursor = str(end) if end < len(ITEMS) else None
|
||||
|
||||
return types.ListResourcesResult(resources=page_items, nextCursor=next_cursor)
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/servers/pagination_example.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/pagination_example.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
#### Client-side Consumption
|
||||
|
||||
<!-- snippet-source examples/snippets/clients/pagination_client.py -->
|
||||
```python
|
||||
"""
|
||||
Example of consuming paginated MCP endpoints from a client.
|
||||
"""
|
||||
|
||||
import asyncio
|
||||
|
||||
from mcp.client.session import ClientSession
|
||||
from mcp.client.stdio import StdioServerParameters, stdio_client
|
||||
from mcp.types import PaginatedRequestParams, Resource
|
||||
|
||||
|
||||
async def list_all_resources() -> None:
|
||||
"""Fetch all resources using pagination."""
|
||||
async with stdio_client(StdioServerParameters(command="uv", args=["run", "mcp-simple-pagination"])) as (
|
||||
read,
|
||||
write,
|
||||
):
|
||||
async with ClientSession(read, write) as session:
|
||||
await session.initialize()
|
||||
|
||||
all_resources: list[Resource] = []
|
||||
cursor = None
|
||||
|
||||
while True:
|
||||
# Fetch a page of resources
|
||||
result = await session.list_resources(params=PaginatedRequestParams(cursor=cursor))
|
||||
all_resources.extend(result.resources)
|
||||
|
||||
print(f"Fetched {len(result.resources)} resources")
|
||||
|
||||
# Check if there are more pages
|
||||
if result.nextCursor:
|
||||
cursor = result.nextCursor
|
||||
else:
|
||||
break
|
||||
|
||||
print(f"Total resources: {len(all_resources)}")
|
||||
|
||||
|
||||
if __name__ == "__main__":
|
||||
asyncio.run(list_all_resources())
|
||||
```
|
||||
|
||||
_Full example: [examples/snippets/clients/pagination_client.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/clients/pagination_client.py)_
|
||||
<!-- /snippet-source -->
|
||||
|
||||
#### Key Points
|
||||
|
||||
- **Cursors are opaque strings** - the server defines the format (numeric offsets, timestamps, etc.)
|
||||
- **Return `nextCursor=None`** when there are no more pages
|
||||
- **Backward compatible** - clients that don't support pagination will still work (they'll just get the first page)
|
||||
- **Flexible page sizes** - Each endpoint can define its own page size based on data characteristics
|
||||
|
||||
See the [simple-pagination example](../examples/servers/simple-pagination) for a complete implementation.
|
||||
For the low-level server API, pagination, and direct handler registration, see [Low-Level Server](low-level-server.md).
|
||||
|
|
|
|||
|
|
@ -62,7 +62,7 @@ async def run():
|
|||
# Read a resource (greeting resource from fastmcp_quickstart)
|
||||
resource_content = await session.read_resource(AnyUrl("greeting://World"))
|
||||
content_block = resource_content.contents[0]
|
||||
if isinstance(content_block, types.TextContent):
|
||||
if isinstance(content_block, types.TextResourceContents):
|
||||
print(f"Resource content: {content_block.text}")
|
||||
|
||||
# Call a tool (add tool from fastmcp_quickstart)
|
||||
|
|
|
|||
|
|
@ -14,7 +14,9 @@ nav:
|
|||
- Introduction: index.md
|
||||
- Installation: installation.md
|
||||
- Documentation:
|
||||
- Concepts: concepts.md
|
||||
- Building Servers: server.md
|
||||
- Writing Clients: client.md
|
||||
- Protocol Features: protocol.md
|
||||
- Low-Level Server: low-level-server.md
|
||||
- Authorization: authorization.md
|
||||
- Testing: testing.md
|
||||
|
|
|
|||
Loading…
Reference in a new issue