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// MCP Servers

python-sdk

The official Python SDK for Model Context Protocol servers and clients

// MCP Servers[ cli ][ api ][ desktop ][ web ][ mobile ][ claude ]#claude#mcp-serversMIT$open-sourceupdated 15 days ago
Actively maintained
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last commit 6 days ago
last release 8 days ago
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// install
{
  "mcpServers": {
    "python-sdk": {
      "command": "npx",
      "args": ["-y", "https://github.com/modelcontextprotocol/python-sdk"]
    }
  }
}

MCP Python SDK

Python implementation of the Model Context Protocol (MCP)

[![PyPI][pypi-badge]][pypi-url] [![MIT licensed][mit-badge]][mit-url] [![Python Version][python-badge]][python-url] [![Documentation][docs-badge]][docs-url] [![Protocol][protocol-badge]][protocol-url] [![Specification][spec-badge]][spec-url]

[!NOTE] This README documents v1.x of the MCP Python SDK (the current stable release).

v2 is in alpha. Pre-releases are published to PyPI as 2.0.0aN and can be installed with an explicit pin, for example pip install mcp==2.0.0a1. See README.v2.md for the v2 documentation and the migration guide for what's changed. We're targeting a beta on 2026-06-30 and a stable v2 on 2026-07-27. If your package depends on mcp, add a <2 upper bound to your version constraint (for example mcp>=1.27,<2) before the stable release lands.

For v1.x code and documentation, see the v1.x branch. v1.x is in maintenance mode and continues to receive critical bug fixes and security patches.

Overview

The Model Context Protocol allows applications to provide context for LLMs in a standardized way, separating the concerns of providing context from the actual LLM interaction. This Python SDK implements the full MCP specification, making it easy to:

  • Build MCP clients that can connect to any MCP server
  • Create MCP servers that expose resources, prompts and tools
  • Use standard transports like stdio, SSE, and Streamable HTTP
  • Handle all MCP protocol messages and lifecycle events

Installation

Adding MCP to your python project

We recommend using uv to manage your Python projects.

If you haven't created a uv-managed project yet, create one:

uv init mcp-server-demo
cd mcp-server-demo

Then add MCP to your project dependencies:

uv add "mcp[cli]"

Alternatively, for projects using pip for dependencies:

pip install "mcp[cli]"

Running the standalone MCP development tools

To run the mcp command with uv:

uv run mcp

Quickstart

Let's create a simple MCP server that exposes a calculator tool and some data:

"""
FastMCP quickstart example.

Run from the repository root:
    uv run examples/snippets/servers/fastmcp_quickstart.py
"""

from mcp.server.fastmcp import FastMCP

# Create an MCP server
mcp = FastMCP("Demo", json_response=True)


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


# Add a dynamic greeting resource
@mcp.resource("greeting://{name}")
def get_greeting(name: str) -> str:
    """Get a personalized greeting"""
    return f"Hello, {name}!"


# Add a prompt
@mcp.prompt()
def greet_user(name: str, style: str = "friendly") -> str:
    """Generate a greeting prompt"""
    styles = {
        "friendly": "Please write a warm, friendly greeting",
        "formal": "Please write a formal, professional greeting",
        "casual": "Please write a casual, relaxed greeting",
    }

    return f"{styles.get(style, styles['friendly'])} for someone named {name}."


# Run with streamable HTTP transport
if __name__ == "__main__":
    mcp.run(transport="streamable-http")

Full example: examples/snippets/servers/fastmcp_quickstart.py

You can install this server in Claude Code and interact with it right away. First, run the server:

uv run --with mcp examples/snippets/servers/fastmcp_quickstart.py

Then add it to Claude Code:

claude mcp add --transport http my-server http://localhost:8000/mcp

Alternatively, you can test it with the MCP Inspector. Start the server as above, then in a separate terminal:

npx -y @modelcontextprotocol/inspector

In the inspector UI, connect to http://localhost:8000/mcp.

What is MCP?

The Model Context Protocol (MCP) lets you build servers that expose data and functionality to LLM applications in a secure, standardized way. Think of it like a web API, but specifically designed for LLM interactions. MCP servers can:

  • Expose data through Resources (think of these sort of like GET endpoints; they are used to load information into the LLM's context)
  • Provide functionality through Tools (sort of like POST endpoints; they are used to execute code or otherwise produce a side effect)
  • Define interaction patterns through Prompts (reusable templates for LLM interactions)
  • And more!

Core Concepts

Server

The FastMCP server is your core interface to the MCP protocol. It handles connection management, protocol compliance, and message routing:

"""Example showing lifespan support for startup/shutdown with strong typing."""

from collections.abc import AsyncIterator
from contextlib import asynccontextmanager
from dataclasses import dataclass

from mcp.server.fastmcp import Context, FastMCP
from mcp.server.session import ServerSession


# Mock database class for example
class Database:
    """Mock database class for example."""

    @classmethod
    async def connect(cls) -> "Database":
        """Connect to database."""
        return cls()

    async def disconnect(self) -> None:
        """Disconnect from database."""
        pass

    def query(self) -> str:
        """Execute a query."""
        return "Query result"


@dataclass
class AppContext:
    """Application context with typed dependencies."""

    db: Database


@asynccontextmanager
async def app_lifespan(server: FastMCP) -> AsyncIterator[AppContext]:
    """Manage application lifecycle with type-safe context."""
    # Initialize on startup
    db = await Database.connect()
    try:
        yield AppContext(db=db)
    finally:
        # Cleanup on shutdown
        await db.disconnect()


# Pass lifespan to server
mcp = FastMCP("My App", lifespan=app_lifespan)


# Access type-safe lifespan context in tools
@mcp.tool()
def query_db(ctx: Context[ServerSession, AppContext]) -> str:
    """Tool that uses initialized resources."""
    db = ctx.request_context.lifespan_context.db
    return db.query()

Full example: examples/snippets/servers/lifespan_example.py

Resources

Resources are how you expose data to LLMs. They're similar to GET endpoints in a REST API - they provide data but shouldn't perform significant computation or have side effects:

from mcp.server.fastmcp import FastMCP

mcp = FastMCP(name="Resource Example")


@mcp.resource("file://documents/{name}")
def read_document(name: str) -> str:
    """Read a document by name."""
    # This would normally read from disk
    return f"Content of {name}"


@mcp.resource("config://settings")
def get_settings() -> str:
    """Get application settings."""
    return """{
  "theme": "dark",
  "language": "en",
  "debug": false
}"""

Full example: examples/snippets/servers/basic_resource.py

Tools

Tools let LLMs take actions through your server. Unlike resources, tools are expected to perform computation and have side effects:

from mcp.server.fastmcp import FastMCP

mcp = FastMCP(name="Tool Example")


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


@mcp.tool()
def get_weather(city: str, unit: str = "celsius") -> str:
    """Get weather for a city."""
    # This would normally call a weather API
    return f"Weather in {city}: 22degrees{unit[0].upper()}"

Full example: examples/snippets/servers/basic_tool.py

Tools can optionally receive a Context object by including a parameter with the Context type annotation. This context is automatically injected by the FastMCP framework and provides access to MCP capabilities:

from mcp.server.fastmcp import Context, FastMCP
from mcp.server.session import ServerSession

mcp = FastMCP(name="Progress Example")


@mcp.tool()
async def long_running_task(task_name: str, ctx: Context[ServerSession, None], steps: int = 5) -> str:
    """Execute a task with progress updates."""
    await ctx.info(f"Starting: {task_name}")

    for i in range(steps):
        progress = (i + 1) / steps
        await ctx.report_progress(
            progress=progress,
            total=1.0,
            message=f"Step {i + 1}/{steps}",
        )
        await ctx.debug(f"Completed step {i + 1}")

    return f"Task '{task_name}' completed"

Full example: examples/snippets/servers/tool_progress.py

Structured Output

Tools will return structured results by default, if their return type annotation is compatible. Otherwise, they will return unstructured results.

Structured output supports these return types:

  • Pydantic models (BaseModel subclasses)
  • TypedDicts
  • Dataclasses and other classes with type hints
  • dict[str, T] (where T is any JSON-serializable type)
  • Primitive types (str, int, float, bool, bytes, None) - wrapped in {"result": value}
  • Generic types (list, tuple, Union, Optional, etc.) - wrapped in {"result": value}

Classes without type hints cannot be serialized for structured output. Only classes with properly annotated attributes will be converted to Pydantic models for schema generation and validation.

Structured results are automatically validated against the output schema generated from the annotation. This ensures the tool returns well-typed, validated data that clients can easily process.

Note: For backward compatibility, unstructured results are also returned. Unstructured results are provided for backward compatibility with previous versions of the MCP specification, and are quirks-compatible with previous versions of FastMCP in the current version of the SDK.

Note: In cases where a tool function's return type annotation causes the tool to be classified as structured and this is undesirable, the classification can be suppressed by passing structured_output=False to the @tool decorator.

Advanced: Direct CallToolResult

For full control over tool responses including the _meta field (for passing data to client applications without exposing it to the model), you can return CallToolResult directly:

"""Example showing direct CallToolResult return for advanced control."""

from typing import Annotated

from pydantic import BaseModel

from mcp.server.fastmcp import FastMCP
from mcp.types import CallToolResult, TextContent

mcp = FastMCP("CallToolResult Example")


class ValidationModel(BaseModel):
    """Model for validating structured output."""

    status: str
    data: dict[str, int]


@mcp.tool()
def advanced_tool() -> CallToolResult:
    """Return CallToolResult directly for full control including _meta field."""
    return CallToolResult(
        content=[TextContent(type="text", text="Response visible to the model")],
        _meta={"hidden": "data for client applications only"},
    )


@mcp.tool()
def validated_tool() -> Annotated[CallToolResult, ValidationModel]:
    """Return CallToolResult with structured output validation."""
    return CallToolResult(
        content=[TextContent(type="text", text="Validated response")],
        structuredContent={"status": "success", "data": {"result": 42}},
        _meta={"internal": "metadata"},
    )


@mcp.tool()
def empty_result_tool() -> CallToolResult:
    """For empty results, return CallToolResult with empty content."""
    return CallToolResult(content=[])

Full example: examples/snippets/servers/direct_call_tool_result.py

Important: CallToolResult must always be returned (no Optional or Union). For empty results, use CallToolResult(content=[]). For optional simple types, use str | None without CallToolResult.

"""Example showing structured output with tools."""

from typing import TypedDict

from pydantic import BaseModel, Field

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("Structured Output Example")


# Using Pydantic models for rich structured data
class WeatherData(BaseModel):
    """Weather information structure."""

    temperature: float = Field(description="Temperature in Celsius")
    humidity: float = Field(description="Humidity percentage")
    condition: str
    wind_speed: float


@mcp.tool()
def get_weather(city: str) -> WeatherData:
    """Get weather for a city - returns structured data."""
    # Simulated weather data
    return WeatherData(
        temperature=22.5,
        humidity=45.0,
        condition="sunny",
        wind_speed=5.2,
    )


# Using TypedDict for simpler structures
class LocationInfo(TypedDict):
    latitude: float
    longitude: float
    name: str


@mcp.tool()
def get_location(address: str) -> LocationInfo:
    """Get location coordinates"""
    return LocationInfo(latitude=51.5074, longitude=-0.1278, name="London, UK")


# Using dict[str, Any] for flexible schemas
@mcp.tool()
def get_statistics(data_type: str) -> dict[str, float]:
    """Get various statistics"""
    return {"mean": 42.5, "median": 40.0, "std_dev": 5.2}


# Ordinary classes with type hints work for structured output
class UserProfile:
    name: str
    age: int
    email: str | None = None

    def __init__(self, name: str, age: int, email: str | None = None):
        self.name = name
        self.age = age
        self.email = email


@mcp.tool()
def get_user(user_id: str) -> UserProfile:
    """Get user profile - returns structured data"""
    return UserProfile(name="Alice", age=30, email="[email protected]")


# Classes WITHOUT type hints cannot be used for structured output
class UntypedConfig:
    def __init__(self, setting1, setting2):  # type: ignore[reportMissingParameterType]
        self.setting1 = setting1
        self.setting2 = setting2


@mcp.tool()
def get_config() -> UntypedConfig:
    """This returns unstructured output - no schema generated"""
    return UntypedConfig("value1", "value2")


# Lists and other types are wrapped automatically
@mcp.tool()
def list_cities() -> list[str]:
    """Get a list of cities"""
    return ["London", "Paris", "Tokyo"]
    # Returns: {"result": ["London", "Paris", "Tokyo"]}


@mcp.tool()
def get_temperature(city: str) -> float:
    """Get temperature as a simple float"""
    return 22.5
    # Returns: {"result": 22.5}

Full example: examples/snippets/servers/structured_output.py

Prompts

Prompts are reusable templates that help LLMs interact with your server effectively:

from mcp.server.fastmcp import FastMCP
from mcp.server.fastmcp.prompts import base

mcp = FastMCP(name="Prompt Example")


@mcp.prompt(title="Code Review")
def review_code(code: str) -> str:
    return f"Please review this code:\n\n{code}"


@mcp.prompt(title="Debug Assistant")
def debug_error(error: str) -> list[base.Message]:
    return [
        base.UserMessage("I'm seeing this error:"),
        base.UserMessage(error),
        base.AssistantMessage("I'll help debug that. What have you tried so far?"),
    ]

Full example: examples/snippets/servers/basic_prompt.py

Icons

MCP servers can provide icons for UI display. Icons can be added to the server implementation, tools, resources, and prompts:

from mcp.server.fastmcp import FastMCP, Icon

# Create an icon from a file path or URL
icon = Icon(
    src="icon.png",
    mimeType="image/png",
    sizes="64x64"
)

# Add icons to server
mcp = FastMCP(
    "My Server",
    website_url="https://example.com",
    icons=[icon]
)

# Add icons to tools, resources, and prompts
@mcp.tool(icons=[icon])
def my_tool():
    """Tool with an icon."""
    return "result"

@mcp.resource("demo://resource", icons=[icon])
def my_resource():
    """Resource with an icon."""
    return "content"

Full example: examples/fastmcp/icons_demo.py

Images

FastMCP provides an Image class that automatically handles image data:

"""Example showing image handling with FastMCP."""

from PIL import Image as PILImage

from mcp.server.fastmcp import FastMCP, Image

mcp = FastMCP("Image Example")


@mcp.tool()
def create_thumbnail(image_path: str) -> Image:
    """Create a thumbnail from an image"""
    img = PILImage.open(image_path)
    img.thumbnail((100, 100))
    return Image(data=img.tobytes(), format="png")

Full example: examples/snippets/servers/images.py

Context

The Context object is automatically injected into tool and resource functions that request it via type hints. It provides access to MCP capabilities like logging, progress reporting, resource reading, user interaction, and request metadata.

Getting Context in Functions

To use context in a tool or resource function, add a parameter with the Context type annotation:

from mcp.server.fastmcp import Context, FastMCP

mcp = FastMCP(name="Context Example")


@mcp.tool()
async def my_tool(x: int, ctx: Context) -> str:
    """Tool that uses context capabilities."""
    # The context parameter can have any name as long as it's type-annotated
    return await process_with_context(x, ctx)

Context Properties and Methods

The Context object provides the following capabilities:

  • ctx.request_id - Unique ID for the current request
  • ctx.client_id - Client ID if available
  • ctx.fastmcp - Access to the FastMCP server instance (see FastMCP Properties)
  • ctx.session - Access to the underlying session for advanced communication (see Session Properties and Methods)
  • ctx.request_context - Access to request-specific data and lifespan resources (see Request Context Properties)
  • await ctx.debug(message) - Send debug log message
  • await ctx.info(message) - Send info log message
  • await ctx.warning(message) - Send warning log message
  • await ctx.error(message) - Send error log message
  • await ctx.log(level, message, logger_name=None) - Send log with custom level
  • await ctx.report_progress(progress, total=None, message=None) - Report operation progress
  • await ctx.read_resource(uri) - Read a resource by URI
  • await ctx.elicit(message, schema) - Request additional information from user with validation
from mcp.server.fastmcp import Context, FastMCP
from mcp.server.session import ServerSession

mcp = FastMCP(name="Progress Example")


@mcp.tool()
async def long_running_task(task_name: str, ctx: Context[ServerSession, None], steps: int = 5) -> str:
    """Execute a task with progress updates."""
    await ctx.info(f"Starting: {task_name}")

    for i in range(steps):
        progress = (i + 1) / steps
        await ctx.report_progress(
            progress=progress,
            total=1.0,
            message=f"Step {i + 1}/{steps}",
        )
        await ctx.debug(f"Completed step {i + 1}")

    return f"Task '{task_name}' completed"

Full example: examples/snippets/servers/tool_progress.py

Completions

MCP supports providing completion suggestions for prompt arguments and resource template parameters. With the context parameter, servers can provide completions based on previously resolved values:

Client usage:

"""
cd to the `examples/snippets` directory and run:
    uv run completion-client
"""

import asyncio
import os

from mcp import ClientSession, StdioServerParameters
from mcp.client.stdio import stdio_client
from mcp.types import PromptReference, ResourceTemplateReference

# Create server parameters for stdio connection
server_params = StdioServerParameters(
    command="uv",  # Using uv to run the server
    args=["run", "server", "completion", "stdio"],  # Server with completion support
    env={"UV_INDEX": os.environ.get("UV_INDEX", "")},
)


async def run():
    """Run the completion client example."""
    async with stdio_client(server_params) as (read, write):
        async with ClientSession(read, write) as session:
            # Initialize the connection
            await session.initialize()

            # List available resource templates
            templates = await session.list_resource_templates()
            print("Available resource templates:")
            for template in templates.resourceTemplates:
                print(f"  - {template.uriTemplate}")

            # List available prompts
            prompts = await session.list_prompts()
            print("\nAvailable prompts:")
            for prompt in prompts.prompts:
                print(f"  - {prompt.name}")

            # Complete resource template arguments
            if templates.resourceTemplates:
                template = templates.resourceTemplates[0]
                print(f"\nCompleting arguments for resource template: {template.uriTemplate}")

                # Complete without context
                result = await session.complete(
                    ref=ResourceTemplateReference(type="ref/resource", uri=template.uriTemplate),
                    argument={"name": "owner", "value": "model"},
                )
                print(f"Completions for 'owner' starting with 'model': {result.completion.values}")

                # Complete with context - repo suggestions based on owner
                result = await session.complete(
                    ref=ResourceTemplateReference(type="ref/resource", uri=template.uriTemplate),
                    argument={"name": "repo", "value": ""},
                    context_arguments={"owner": "modelcontextprotocol"},
                )
                print(f"Completions for 'repo' with owner='modelcontextprotocol': {result.completion.values}")

            # Complete prompt arguments
            if prompts.prompts:
                prompt_name = prompts.prompts[0].name
                print(f"\nCompleting arguments for prompt: {prompt_name}")

                result = await session.complete(
                    ref=PromptReference(type="ref/prompt", name=prompt_name),
                    argument={"name": "style", "value": ""},
                )
                print(f"Completions for 'style' argument: {result.completion.values}")


def main():
    """Entry point for the completion client."""
    asyncio.run(run())


if __name__ == "__main__":
    main()

Full example: examples/snippets/clients/completion_client.py

Elicitation

Request additional information from users. This example shows an Elicitation during a Tool Call:

"""Elicitation examples demonstrating form and URL mode elicitation.

Form mode elicitation collects structured, non-sensitive data through a schema.
URL mode elicitation directs users to external URLs for sensitive operations
like OAuth flows, credential collection, or payment processing.
"""

import uuid

from pydantic import BaseModel, Field

from mcp.server.fastmcp import Context, FastMCP
from mcp.server.session import ServerSession
from mcp.shared.exceptions import UrlElicitationRequiredError
from mcp.types import ElicitRequestURLParams

mcp = FastMCP(name="Elicitation Example")


class BookingPreferences(BaseModel):
    """Schema for collecting user preferences."""

    checkAlternative: bool = Field(description="Would you like to check another date?")
    alternativeDate: str = Field(
        default="2024-12-26",
        description="Alternative date (YYYY-MM-DD)",
    )


@mcp.tool()
async def book_table(date: str, time: str, party_size: int, ctx: Context[ServerSession, None]) -> str:
    """Book a table with date availability check.

    This demonstrates form mode elicitation for collecting non-sensitive user input.
    """
    # Check if date is available
    if date == "2024-12-25":
        # Date unavailable - ask user for alternative
        result = await ctx.elicit(
            message=(f"No tables available for {party_size} on {date}. Would you like to try another date?"),
            schema=BookingPreferences,
        )

        if result.action == "accept" and result.data:
            if result.data.checkAlternative:
                return f"[SUCCESS] Booked for {result.data.alternativeDate}"
            return "[CANCELLED] No booking made"
        return "[CANCELLED] Booking cancelled"

    # Date available
    return f"[SUCCESS] Booked for {date} at {time}"


@mcp.tool()
async def secure_payment(amount: float, ctx: Context[ServerSession, None]) -> str:
    """Process a secure payment requiring URL confirmation.

    This demonstrates URL mode elicitation using ctx.elicit_url() for
    operations that require out-of-band user interaction.
    """
    elicitation_id = str(uuid.uuid4())

    result = await ctx.elicit_url(
        message=f"Please confirm payment of ${amount:.2f}",
        url=f"https://payments.example.com/confirm?amount={amount}&id={elicitation_id}",
        elicitation_id=elicitation_id,
    )

    if result.action == "accept":
        # In a real app, the payment confirmation would happen out-of-band
        # and you'd verify the payment status from your backend
        return f"Payment of ${amount:.2f} initiated - check your browser to complete"
    elif result.action == "decline":
        return "Payment declined by user"
    return "Payment cancelled"


@mcp.tool()
async def connect_service(service_name: str, ctx: Context[ServerSession, None]) -> str:
    """Connect to a third-party service requiring OAuth authorization.

    This demonstrates the "throw error" pattern using UrlElicitationRequiredError.
    Use this pattern when the tool cannot proceed without user authorization.
    """
    elicitation_id = str(uuid.uuid4())

    # Raise UrlElicitationRequiredError to signal that the client must complete
    # a URL elicitation before this request can be processed.
    # The MCP framework will convert this to a -32042 error response.
    raise UrlElicitationRequiredError(
        [
            ElicitRequestURLParams(
                mode="url",
                message=f"Authorization required to connect to {service_name}",
                url=f"https://{service_name}.example.com/oauth/authorize?elicit={elicitation_id}",
                elicitationId=elicitation_id,
            )
        ]
    )

Full example: examples/snippets/servers/elicitation.py

Elicitation schemas support default values for all field types. Default values are automatically included in the JSON schema sent to clients, allowing them to pre-populate forms.

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

Sampling

Tools can interact with LLMs through sampling (generating text):

from mcp.server.fastmcp import Context, FastMCP
from mcp.server.session import ServerSession
from mcp.types import SamplingMessage, TextContent

mcp = FastMCP(name="Sampling Example")


@mcp.tool()
async def generate_poem(topic: str, ctx: Context[ServerSession, None]) -> str:
    """Generate a poem using LLM sampling."""
    prompt = f"Write a short poem about {topic}"

    result = await ctx.session.create_message(
        messages=[
            SamplingMessage(
                role="user",
                content=TextContent(type="text", text=prompt),
            )
        ],
        max_tokens=100,
    )

    # Since we're not passing tools param, result.content is single content
    if result.content.type == "text":
        return result.content.text
    return str(result.content)

Full example: examples/snippets/servers/sampling.py

Logging and Notifications

Tools can send logs and notifications through the context:

from mcp.server.fastmcp import Context, FastMCP
from mcp.server.session import ServerSession

mcp = FastMCP(name="Notifications Example")


@mcp.tool()
async def process_data(data: str, ctx: Context[ServerSession, None]) -> str:
    """Process data with logging."""
    # Different log levels
    await ctx.debug(f"Debug: Processing '{data}'")
    await ctx.info("Info: Starting processing")
    await ctx.warning("Warning: This is experimental")
    await ctx.error("Error: (This is just a demo)")

    # Notify about resource changes
    await ctx.session.send_resource_list_changed()

    return f"Processed: {data}"

Full example: examples/snippets/servers/notifications.py

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 and implements RFC 9728 (Protected Resource Metadata) for AS discovery.

MCP servers can use authentication by providing an implementation of the TokenVerifier protocol:

"""
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

For a complete example with separate Authorization Server and Resource Server implementations, see 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 for more details on implementing token validation.

FastMCP Properties

The FastMCP server instance accessible via ctx.fastmcp provides access to server configuration and metadata:

  • ctx.fastmcp.name - The server's name as defined during initialization
  • ctx.fastmcp.instructions - Server instructions/description provided to clients
  • ctx.fastmcp.website_url - Optional website URL for the server
  • ctx.fastmcp.icons - Optional list of icons for UI display
  • ctx.fastmcp.settings - Complete server configuration object containing:
    • debug - Debug mode flag
    • log_level - Current logging level
    • host and port - Server network configuration
    • mount_path, sse_path, streamable_http_path - Transport paths
    • stateless_http - Whether the server operates in stateless mode
    • And other configuration options
@mcp.tool()
def server_info(ctx: Context) -> dict:
    """Get information about the current server."""
    return {
        "name": ctx.fastmcp.name,
        "instructions": ctx.fastmcp.instructions,
        "debug_mode": ctx.fastmcp.settings.debug,
        "log_level": ctx.fastmcp.settings.log_level,
        "host": ctx.fastmcp.settings.host,
        "port": ctx.fastmcp.settings.port,
    }

Session Properties and Methods

The session object accessible via ctx.session provides advanced control over client communication:

  • ctx.session.client_params - Client initialization parameters and declared capabilities
  • await ctx.session.send_log_message(level, data, logger) - Send log messages with full control
  • await ctx.session.create_message(messages, max_tokens) - Request LLM sampling/completion
  • await ctx.session.send_progress_notification(token, progress, total, message) - Direct progress updates
  • await ctx.session.send_resource_updated(uri) - Notify clients that a specific resource changed
  • await ctx.session.send_resource_list_changed() - Notify clients that the resource list changed
  • await ctx.session.send_tool_list_changed() - Notify clients that the tool list changed
  • await ctx.session.send_prompt_list_changed() - Notify clients that the prompt list changed
@mcp.tool()
async def notify_data_update(resource_uri: str, ctx: Context) -> str:
    """Update data and notify clients of the change."""
    # Perform data update logic here
    
    # Notify clients that this specific resource changed
    await ctx.session.send_resource_updated(AnyUrl(resource_uri))
    
    # If this affects the overall resource list, notify about that too
    await ctx.session.send_resource_list_changed()
    
    return f"Updated {resource_uri} and notified clients"

Request Context Properties

The request context accessible via ctx.request_context contains request-specific information and resources:

  • ctx.request_context.lifespan_context - Access to resources initialized during server startup
    • Database connections, configuration objects, shared services
    • Type-safe access to resources defined in your server's lifespan function
  • ctx.request_context.meta - Request metadata from the client including:
    • progressToken - Token for progress notifications
    • Other client-provided metadata
  • ctx.request_context.request - The original MCP request object for advanced processing
  • ctx.request_context.request_id - Unique identifier for this request
# Example with typed lifespan context
@dataclass
class AppContext:
    db: Database
    config: AppConfig

@mcp.tool()
def query_with_config(query: str, ctx: Context) -> str:
    """Execute a query using shared database and configuration."""
    # Access typed lifespan context
    app_ctx: AppContext = ctx.request_context.lifespan_context
    
    # Use shared resources
    connection = app_ctx.db
    settings = app_ctx.config
    
    # Execute query with configuration
    result = connection.execute(query, timeout=settings.query_timeout)
    return str(result)

Full lifespan example: examples/snippets/servers/lifespan_example.py

Running Your Server

Development Mode

The fastest way to test and debug your server is with the MCP Inspector:

uv run mcp dev server.py

# Add dependencies
uv run mcp dev server.py --with pandas --with numpy

# Mount local code
uv run mcp dev server.py --with-editable .

Claude Desktop Integration

Once your server is ready, install it in Claude Desktop:

uv run mcp install server.py

# Custom name
uv run mcp install server.py --name "My Analytics Server"

# Environment variables
uv run mcp install server.py -v API_KEY=abc123 -v DB_URL=postgres://...
uv run mcp install server.py -f .env

Direct Execution

For advanced scenarios like custom deployments:

"""Example showing direct execution of an MCP server.

This is the simplest way to run an MCP server directly.
cd to the `examples/snippets` directory and run:
    uv run direct-execution-server
    or
    python servers/direct_execution.py
"""

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("My App")


@mcp.tool()
def hello(name: str = "World") -> str:
    """Say hello to someone."""
    return f"Hello, {name}!"


def main():
    """Entry point for the direct execution server."""
    mcp.run()


if __name__ == "__main__":
    main()

Full example: examples/snippets/servers/direct_execution.py

Run it with:

python servers/direct_execution.py
# or
uv run mcp run servers/direct_execution.py

Note that uv run mcp run or uv run mcp dev only supports server using FastMCP and not the low-level server variant.

Streamable HTTP Transport

Note: Streamable HTTP transport is the recommended transport for production deployments. Use stateless_http=True and json_response=True for optimal scalability.

"""
Run from the repository root:
    uv run examples/snippets/servers/streamable_config.py
"""

from mcp.server.fastmcp import FastMCP

# Stateless server with JSON responses (recommended)
mcp = FastMCP("StatelessServer", stateless_http=True, json_response=True)

# Other configuration options:
# Stateless server with SSE streaming responses
# mcp = FastMCP("StatelessServer", stateless_http=True)

# Stateful server with session persistence
# mcp = FastMCP("StatefulServer")


# Add a simple tool to demonstrate the server
@mcp.tool()
def greet(name: str = "World") -> str:
    """Greet someone by name."""
    return f"Hello, {name}!"


# Run server with streamable_http transport
if __name__ == "__main__":
    mcp.run(transport="streamable-http")

Full example: examples/snippets/servers/streamable_config.py

You can mount multiple FastMCP servers in a Starlette application:

"""
Run from the repository root:
    uvicorn examples.snippets.servers.streamable_starlette_mount:app --reload
"""

import contextlib

from starlette.applications import Starlette
from starlette.routing import Mount

from mcp.server.fastmcp import FastMCP

# Create the Echo server
echo_mcp = FastMCP(name="EchoServer", stateless_http=True, json_response=True)


@echo_mcp.tool()
def echo(message: str) -> str:
    """A simple echo tool"""
    return f"Echo: {message}"


# Create the Math server
math_mcp = FastMCP(name="MathServer", stateless_http=True, json_response=True)


@math_mcp.tool()
def add_two(n: int) -> int:
    """Tool to add two to the input"""
    return n + 2


# Create a combined lifespan to manage both session managers
@contextlib.asynccontextmanager
async def lifespan(app: Starlette):
    async with contextlib.AsyncExitStack() as stack:
        await stack.enter_async_context(echo_mcp.session_manager.run())
        await stack.enter_async_context(math_mcp.session_manager.run())
        yield


# Create the Starlette app and mount the MCP servers
app = Starlette(
    routes=[
        Mount("/echo", echo_mcp.streamable_http_app()),
        Mount("/math", math_mcp.streamable_http_app()),
    ],
    lifespan=lifespan,
)

# Note: Clients connect to http://localhost:8000/echo/mcp and http://localhost:8000/math/mcp
# To mount at the root of each path (e.g., /echo instead of /echo/mcp):
# echo_mcp.settings.streamable_http_path = "/"
# math_mcp.settings.streamable_http_path = "/"

Full example: examples/snippets/servers/streamable_starlette_mount.py

For low level server with Streamable HTTP implementations, see:

The streamable HTTP transport supports:

  • Stateful and stateless operation modes
  • Resumability with event stores
  • JSON or SSE response formats
  • Better scalability for multi-node deployments

CORS Configuration for Browser-Based Clients

If you'd like your server to be accessible by browser-based MCP clients, you'll need to configure CORS headers. The Mcp-Session-Id header must be exposed for browser clients to access it:

from starlette.applications import Starlette
from starlette.middleware.cors import CORSMiddleware

# Create your Starlette app first
starlette_app = Starlette(routes=[...])

# Then wrap it with CORS middleware
starlette_app = CORSMiddleware(
    starlette_app,
    allow_origins=["*"],  # Configure appropriately for production
    allow_methods=["GET", "POST", "DELETE"],  # MCP streamable HTTP methods
    expose_headers=["Mcp-Session-Id"],
)

This configuration is necessary because:

  • The MCP streamable HTTP transport uses the Mcp-Session-Id header for session management
  • Browsers restrict access to response headers unless explicitly exposed via CORS
  • Without this configuration, browser-based clients won't be able to read the session ID from initialization responses

Mounting to an Existing ASGI Server

By default, SSE servers are mounted at /sse and Streamable HTTP servers are mounted at /mcp. You can customize these paths using the methods described below.

For more information on mounting applications in Starlette, see the Starlette documentation.

StreamableHTTP servers

You can mount the StreamableHTTP server to an existing ASGI server using the streamable_http_app method. This allows you to integrate the StreamableHTTP server with other ASGI applications.

Basic mounting
"""
Basic example showing how to mount StreamableHTTP server in Starlette.

Run from the repository root:
    uvicorn examples.snippets.servers.streamable_http_basic_mounting:app --reload
"""

import contextlib

from starlette.applications import Starlette
from starlette.routing import Mount

from mcp.server.fastmcp import FastMCP

# Create MCP server
mcp = FastMCP("My App", json_response=True)


@mcp.tool()
def hello() -> str:
    """A simple hello tool"""
    return "Hello from MCP!"


# Create a lifespan context manager to run the session manager
@contextlib.asynccontextmanager
async def lifespan(app: Starlette):
    async with mcp.session_manager.run():
        yield


# Mount the StreamableHTTP server to the existing ASGI server
app = Starlette(
    routes=[
        Mount("/", app=mcp.streamable_http_app()),
    ],
    lifespan=lifespan,
)

Full example: examples/snippets/servers/streamable_http_basic_mounting.py

Host-based routing
"""
Example showing how to mount StreamableHTTP server using Host-based routing.

Run from the repository root:
    uvicorn examples.snippets.servers.streamable_http_host_mounting:app --reload
"""

import contextlib

from starlette.applications import Starlette
from starlette.routing import Host

from mcp.server.fastmcp import FastMCP

# Create MCP server
mcp = FastMCP("MCP Host App", json_response=True)


@mcp.tool()
def domain_info() -> str:
    """Get domain-specific information"""
    return "This is served from mcp.acme.corp"


# Create a lifespan context manager to run the session manager
@contextlib.asynccontextmanager
async def lifespan(app: Starlette):
    async with mcp.session_manager.run():
        yield


# Mount using Host-based routing
app = Starlette(
    routes=[
        Host("mcp.acme.corp", app=mcp.streamable_http_app()),
    ],
    lifespan=lifespan,
)

Full example: examples/snippets/servers/streamable_http_host_mounting.py

Multiple servers with path configuration
"""
Example showing how to mount multiple StreamableHTTP servers with path configuration.

Run from the repository root:
    uvicorn examples.snippets.servers.streamable_http_multiple_servers:app --reload
"""

import contextlib

from starlette.applications import Starlette
from starlette.routing import Mount

from mcp.server.fastmcp import FastMCP

# Create multiple MCP servers
api_mcp = FastMCP("API Server", json_response=True)
chat_mcp = FastMCP("Chat Server", json_response=True)


@api_mcp.tool()
def api_status() -> str:
    """Get API status"""
    return "API is running"


@chat_mcp.tool()
def send_message(message: str) -> str:
    """Send a chat message"""
    return f"Message sent: {message}"


# Configure servers to mount at the root of each path
# This means endpoints will be at /api and /chat instead of /api/mcp and /chat/mcp
api_mcp.settings.streamable_http_path = "/"
chat_mcp.settings.streamable_http_path = "/"


# Create a combined lifespan to manage both session managers
@contextlib.asynccontextmanager
async def lifespan(app: Starlette):
    async with contextlib.AsyncExitStack() as stack:
        await stack.enter_async_context(api_mcp.session_manager.run())
        await stack.enter_async_context(chat_mcp.session_manager.run())
        yield


# Mount the servers
app = Starlette(
    routes=[
        Mount("/api", app=api_mcp.streamable_http_app()),
        Mount("/chat", app=chat_mcp.streamable_http_app()),
    ],
    lifespan=lifespan,
)

Full example: examples/snippets/servers/streamable_http_multiple_servers.py

Path configuration at initialization

view the full README on GitHub.

// compatibility

Platformscli, api, desktop, web, mobile
Operating systems
AI compatibilityclaude
LicenseMIT
Pricingopen-source
LanguagePython

// faq

What is python-sdk?

The official Python SDK for Model Context Protocol servers and clients. It is open-source on GitHub.

Is python-sdk free to use?

python-sdk is open-source under the MIT license, so it is free to use.

What category does python-sdk belong to?

python-sdk is listed under mcp-servers in the Claudeers registry of Claude-compatible tools.

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