langgraph/docs/docs/agents/mcp.md

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Use MCP

The 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.

Use MCP tools

The langchain-mcp-adapters package enables agents to use tools defined across one or more MCP servers.

=== "In an agent"

```python title="Agent using tools defined on MCP servers"
# highlight-next-line
from langchain_mcp_adapters.client import MultiServerMCPClient
from langgraph.prebuilt import create_react_agent

# highlight-next-line
client = MultiServerMCPClient(
    {
        "math": {
            "command": "python",
            # Replace with absolute path to your math_server.py file
            "args": ["/path/to/math_server.py"],
            "transport": "stdio",
        },
        "weather": {
            # Ensure you start your weather server on port 8000
            "url": "http://localhost:8000/mcp",
            "transport": "streamable_http",
        }
    }
)
# highlight-next-line
tools = await client.get_tools()
agent = create_react_agent(
    "anthropic:claude-3-7-sonnet-latest",
    # highlight-next-line
    tools
)
math_response = await agent.ainvoke(
    {"messages": [{"role": "user", "content": "what's (3 + 5) x 12?"}]}
)
weather_response = await agent.ainvoke(
    {"messages": [{"role": "user", "content": "what is the weather in nyc?"}]}
)
```

=== "In a workflow"

```python title="Workflow using MCP tools with ToolNode"
from langchain_mcp_adapters.client import MultiServerMCPClient
from langchain.chat_models import init_chat_model
from langgraph.graph import StateGraph, MessagesState, START, END
from langgraph.prebuilt import ToolNode

# Initialize the model
model = init_chat_model("anthropic:claude-3-5-sonnet-latest")

# Set up MCP client
client = MultiServerMCPClient(
    {
        "math": {
            "command": "python",
            # Make sure to update to the full absolute path to your math_server.py file
            "args": ["./examples/math_server.py"],
            "transport": "stdio",
        },
        "weather": {
            # make sure you start your weather server on port 8000
            "url": "http://localhost:8000/mcp/",
            "transport": "streamable_http",
        }
    }
)
tools = await client.get_tools()

# Bind tools to model
model_with_tools = model.bind_tools(tools)

# Create ToolNode
tool_node = ToolNode(tools)

def should_continue(state: MessagesState):
    messages = state["messages"]
    last_message = messages[-1]
    if last_message.tool_calls:
        return "tools"
    return END

# Define call_model function
async def call_model(state: MessagesState):
    messages = state["messages"]
    response = await model_with_tools.ainvoke(messages)
    return {"messages": [response]}

# Build the graph
builder = StateGraph(MessagesState)
builder.add_node("call_model", call_model)
builder.add_node("tools", tool_node)

builder.add_edge(START, "call_model")
builder.add_conditional_edges(
    "call_model",
    should_continue,
)
builder.add_edge("tools", "call_model")

# Compile the graph
graph = builder.compile()

# Test the graph
math_response = await graph.ainvoke(
    {"messages": [{"role": "user", "content": "what's (3 + 5) x 12?"}]}
)
weather_response = await graph.ainvoke(
    {"messages": [{"role": "user", "content": "what is the weather in nyc?"}]}
)
```

Custom MCP servers

To create your own MCP servers, you can use the mcp library. This library provides a simple way to define tools and run them as servers.

Install the MCP library:

pip install mcp

Use the following reference implementations to test your agent with MCP tool servers.

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("Math")

@mcp.tool()
def add(a: int, b: int) -> int:
    """Add two numbers"""
    return a + b

@mcp.tool()
def multiply(a: int, b: int) -> int:
    """Multiply two numbers"""
    return a * b

if __name__ == "__main__":
    mcp.run(transport="stdio")

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("Weather")

@mcp.tool()
async def get_weather(location: str) -> str:
    """Get weather for location."""
    return "It's always sunny in New York"

if __name__ == "__main__":
    mcp.run(transport="streamable-http")

Additional resources

• MCP documentation
• MCP Transport documentation
• langchain_mcp_adapters