Add resource Link (#974)

src/mcp/server/fastmcp/prompts/base.py

@@ -7,16 +7,16 @@ from typing import Any, Literal
 import pydantic_core
 from pydantic import BaseModel, Field, TypeAdapter, validate_call
 
-from mcp.types import Content, TextContent
+from mcp.types import ContentBlock, TextContent
 
 
 class Message(BaseModel):
     """Base class for all prompt messages."""
 
     role: Literal["user", "assistant"]
-    content: Content
+    content: ContentBlock
 
-    def __init__(self, content: str | Content, **kwargs: Any):
+    def __init__(self, content: str | ContentBlock, **kwargs: Any):
         if isinstance(content, str):
             content = TextContent(type="text", text=content)
         super().__init__(content=content, **kwargs)
@@ -27,7 +27,7 @@ class UserMessage(Message):
 
     role: Literal["user", "assistant"] = "user"
 
-    def __init__(self, content: str | Content, **kwargs: Any):
+    def __init__(self, content: str | ContentBlock, **kwargs: Any):
         super().__init__(content=content, **kwargs)
 
 
@@ -36,7 +36,7 @@ class AssistantMessage(Message):
 
     role: Literal["user", "assistant"] = "assistant"
 
-    def __init__(self, content: str | Content, **kwargs: Any):
+    def __init__(self, content: str | ContentBlock, **kwargs: Any):
         super().__init__(content=content, **kwargs)
 
 

src/mcp/server/fastmcp/server.py

@@ -54,7 +54,7 @@ from mcp.server.transport_security import TransportSecuritySettings
 from mcp.shared.context import LifespanContextT, RequestContext, RequestT
 from mcp.types import (
     AnyFunction,
-    Content,
+    ContentBlock,
     GetPromptResult,
     TextContent,
     ToolAnnotations,
@@ -260,7 +260,7 @@ class FastMCP:
             request_context = None
         return Context(request_context=request_context, fastmcp=self)
 
-    async def call_tool(self, name: str, arguments: dict[str, Any]) -> Sequence[Content]:
+    async def call_tool(self, name: str, arguments: dict[str, Any]) -> Sequence[ContentBlock]:
         """Call a tool by name with arguments."""
         context = self.get_context()
         result = await self._tool_manager.call_tool(name, arguments, context=context)
@@ -878,12 +878,12 @@ class FastMCP:
 
 def _convert_to_content(
     result: Any,
-) -> Sequence[Content]:
+) -> Sequence[ContentBlock]:
     """Convert a result to a sequence of content objects."""
     if result is None:
         return []
 
-    if isinstance(result, Content):
+    if isinstance(result, ContentBlock):
         return [result]
 
     if isinstance(result, Image):

src/mcp/server/lowlevel/server.py

@@ -384,7 +384,7 @@ class Server(Generic[LifespanResultT, RequestT]):
         def decorator(
             func: Callable[
                 ...,
-                Awaitable[Iterable[types.Content]],
+                Awaitable[Iterable[types.ContentBlock]],
             ],
         ):
             logger.debug("Registering handler for CallToolRequest")

src/mcp/types.py

@@ -733,14 +733,28 @@ class EmbeddedResource(BaseModel):
     model_config = ConfigDict(extra="allow")
 
 
-Content = TextContent | ImageContent | AudioContent | EmbeddedResource
+class ResourceLink(Resource):
+    """
+    A resource that the server is capable of reading, included in a prompt or tool call result.
+
+    Note: resource links returned by tools are not guaranteed to appear in the results of `resources/list` requests.
+    """
+
+    type: Literal["resource_link"]
+
+
+ContentBlock = TextContent | ImageContent | AudioContent | ResourceLink | EmbeddedResource
+"""A content block that can be used in prompts and tool results."""
+
+Content: TypeAlias = ContentBlock
+# """DEPRECATED: Content is deprecated, you should use ContentBlock directly."""
 
 
 class PromptMessage(BaseModel):
     """Describes a message returned as part of a prompt."""
 
     role: Role
-    content: Content
+    content: ContentBlock
     model_config = ConfigDict(extra="allow")
 
 
@@ -859,7 +873,7 @@ class CallToolRequest(Request[CallToolRequestParams, Literal["tools/call"]]):
 class CallToolResult(Result):
     """The server's response to a tool call."""
 
-    content: list[Content]
+    content: list[ContentBlock]
     isError: bool = False