langgraph/docs/docs/concepts/mcp.md

MCP

Model Context Protocol (MCP) is an open protocol that standardizes how applications provide tools and context to language models. LangGraph agents can use tools defined on MCP servers through the langchain-mcp-adapters library.

Install the langchain-mcp-adapters library to use MCP tools in LangGraph:

pip install langchain-mcp-adapters

Authenticate to an MCP server

You can set up custom authentication middleware to authenticate a user with an MCP server to get access to user-scoped tools within your LangGraph Platform deployment.

!!! note Custom authentication is a LangGraph Platform feature.

An example architecture for this flow:

sequenceDiagram
  %% Actors
  participant ClientApp as Client
  participant AuthProv  as Auth Provider
  participant LangGraph as LangGraph Backend
  participant SecretStore as Secret Store
  participant MCPServer as MCP Server

  %% Platform login / AuthN
  ClientApp  ->> AuthProv: 1. Login (username / password)
  AuthProv   -->> ClientApp: 2. Return token
  ClientApp  ->> LangGraph: 3. Request with token

  Note over LangGraph: 4. Validate token (@auth.authenticate)
  LangGraph  -->> AuthProv: 5. Fetch user info
  AuthProv   -->> LangGraph: 6. Confirm validity

  %% Fetch user tokens from secret store
  LangGraph  ->> SecretStore: 6a. Fetch user tokens
  SecretStore -->> LangGraph: 6b. Return tokens

  Note over LangGraph: 7. Apply access control (@auth.on.*)

  %% MCP round-trip
  Note over LangGraph: 8. Build MCP client with user token
  LangGraph  ->> MCPServer: 9. Call MCP tool (with header)
  Note over MCPServer: 10. MCP validates header and runs tool
  MCPServer  -->> LangGraph: 11. Tool response

  %% Return to caller
  LangGraph  -->> ClientApp: 12. Return resources / tool output

For more information, see MCP endpoint in LangGraph Server.