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| title | type | weight |
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| Base Protocol | docs | 1 |
The Model Context Protocol (MCP) defines a set of JSON-RPC methods for communication between clients and servers in AI-assisted applications. MCP uses JSON-RPC 2.0 as its base protocol.
Transport
MCP client SHOULD use one of the following transport mechanisms, but are free to use alternative transports where applicable.:
- Standard Input/Output (STDIO)
- Communication occurs through the standard input and output streams. JSON-RPC messages are sent as individual lines over these streams. Each message is a complete JSON object serialized as a single line of text, terminated by a newline character. The client writes requests to the server's standard input and reads responses from the server's standard output. See transports for more details.
- HTTP with Server-Sent Events (SSE)
- This transport uses HTTP (1.1 or above) as the underlying protocol. The client sends requests to the server using standard HTTP POST requests with JSON-RPC payloads. For server-to-client communication, Server-Sent Events (SSE) are employed. The server keeps an open connection to the client and sends messages as SSE events. See transports for more details.
Message Format
All messages in MCP MUST follow the JSON-RPC 2.0 specification. The protocol defines three types of messages:
- Requests
- Responses
- Notifications
Requests
Requests are sent from the client to the server or vice versa. They MUST include a unique id and expect a response.
Responses
Responses are sent in reply to requests. They MUST include the same id as the corresponding request.
Notifications
Notifications are sent from the client to the server or vice versa. They do not expect a response and MUST NOT include an id.
Base Protocol
The base protocol consists of the following JSON-RPC methods:
initialize: Sent from the client to the server to initialize the connection.initialized: Sent from the client to the server after initialization is complete.ping: Sent by either party to check if the other is still alive.
Implementations MUST support these base protocol methods.
Model Context Protocol specific methods
MCP defines methods based on JSON-RPC that clients and servers implement:
Authentication
Authentication mechanisms are not part of the core MCP specification. Implementations MAY provide authentication based on the transport they use..
Versioning
The MCP version is declared in the initialize request and response. Clients and servers MUST agree on a compatible protocol version to proceed with communication.
Specification
The conical specification can be found at Model Context Protocol. The specification of the data format is available in TypeScript (source of truth) and JSON Schema format (generated).