fastmcp-server

FastMCP 3.0 Server Development

Complete reference for building production-ready MCP (Model Context Protocol) servers with FastMCP 3.0 - the fast, Pythonic framework for connecting LLMs to tools and data.

When to use this skill

Use FastMCP Server when:

• Creating a new MCP server in Python
• Adding tools, resources, or prompts to an MCP server
• Implementing authentication (OAuth, OIDC, token verification)
• Setting up middleware for logging, rate limiting, or authorization
• Configuring providers (local, filesystem, skills, custom)
• Building production MCP servers with telemetry and storage
• Upgrading from FastMCP 2.x to 3.0

Key areas covered:

• Tools & Resources (CORE): Decorators, validation, return types, templates
• Context & DI (CORE): MCP context, dependency injection, background tasks
• Authentication (SECURITY): OAuth, OIDC, token verification, proxy patterns
• Authorization (SECURITY): Scope-based and role-based access control
• Middleware (ADVANCED): Request/response pipeline, built-in middleware
• Providers (ADVANCED): Local, filesystem, skills, and custom providers
• Features (ADVANCED): Pagination, sampling, storage, OpenTelemetry, versioning

Quick reference

Core patterns

Create a server with tools:

from fastmcp import FastMCP

mcp = FastMCP("MyServer")

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

Create a resource:

@mcp.resource("data://config")
def get_config() -> dict:
    """Return server configuration"""
    return {"version": "1.0", "debug": False}

Create a resource template:

@mcp.resource("users://{user_id}/profile")
def get_user_profile(user_id: str) -> dict:
    """Get a user's profile by ID"""
    return fetch_user(user_id)

Create a prompt:

@mcp.prompt
def review_code(code: str, language: str = "python") -> str:
    """Review code for best practices"""
    return f"Review this {language} code:\n\n{code}"

Run the server:

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

# Or with transport options:
# mcp.run(transport="sse", host="0.0.0.0", port=8000)

Using context in tools

from fastmcp import FastMCP, Context

mcp = FastMCP("MyServer")

@mcp.tool
def process_data(uri: str, ctx: Context) -> str:
    """Process data with logging and progress"""
    ctx.info(f"Processing {uri}")
    ctx.report_progress(0, 100)
    data = ctx.read_resource(uri)
    ctx.report_progress(100, 100)
    return f"Processed: {data}"

Authentication setup

from fastmcp import FastMCP
from fastmcp.server.auth import BearerAuthProvider

auth = BearerAuthProvider(
    jwks_uri="https://your-provider/.well-known/jwks.json",
    audience="your-api",
    issuer="https://your-provider/"
)

mcp = FastMCP("SecureServer", auth=auth)

Key concepts

Tools

Functions exposed as executable capabilities for LLMs. Decorated with @mcp.tool. Support Pydantic validation, async, custom return types, and annotations (readOnlyHint, destructiveHint).

Resources & Templates

Static or dynamic data sources identified by URIs. Resources use fixed URIs (data://config), templates use parameterized URIs (users://{id}/profile). Support MIME types, annotations, and wildcard parameters.

Context

The Context object provides access to MCP features within tools/resources: logging, progress reporting, resource access, LLM sampling, user elicitation, and session state.

Dependency Injection

Inject values into tool/resource functions using Depends(). Supports HTTP requests, access tokens, custom dependencies, and generator-based cleanup patterns.

Providers

Control where components come from. LocalProvider (default, decorator-based), FileSystemProvider (load from Python files on disk), SkillsProvider (packaged bundles), or custom providers.

Authentication & Authorization

Multiple auth patterns: token verification (JWT, JWKS), OAuth proxy, OIDC proxy, remote OAuth, and full OAuth server. Authorization via scopes on components and middleware.

Middleware

Intercept and modify requests/responses. Built-in middleware for rate limiting, error handling, logging, and response size limits. Custom middleware via @mcp.middleware.

Using the references

Detailed documentation is organized in the references/ folder:

Getting Started

• getting-started/installation.md - Install FastMCP, optional dependencies, verify setup
• getting-started/upgrade-guide.md - Migrate from FastMCP 2.x to 3.0
• getting-started/quickstart.md - First server, tools, resources, prompts, running

Server

• server/server-class.md - FastMCP server configuration, transport options, tag filtering
• server/tools.md - Tool decorator, parameters, validation, return types, annotations
• server/resources-and-templates.md - Resources, templates, URIs, wildcards, MIME types

Context

• context/mcp-context.md - Context object, logging, progress, resource access, sampling
• context/background-tasks.md - Long-running operations with task support
• context/dependency-injection.md - Depends(), custom deps, HTTP request, access tokens
• context/user-elicitation.md - Request structured input from users during execution

Features

• features/icons.md - Custom icons for tools, resources, prompts, and servers
• features/lifespans.md - Server lifecycle management and startup/shutdown hooks
• features/client-logging.md - Send log messages to MCP clients
• features/middleware.md - Request/response pipeline, built-in and custom middleware
• features/pagination.md - Paginate large component lists
• features/progress-reporting.md - Report progress for long-running operations
• features/sampling.md - Request LLM completions from the client
• features/storage-backends.md - Memory, file, and Redis storage for caching and tokens
• features/opentelemetry.md - Distributed tracing and observability
• features/versioning.md - Version components and filter by version ranges

Authentication

• authentication/token-verification.md - JWT, JWKS, introspection, static keys, custom
• authentication/remote-oauth.md - Delegate auth to upstream OAuth provider
• authentication/oauth-proxy.md - Full OAuth proxy with PKCE, client management
• authentication/oidc-proxy.md - OpenID Connect proxy with auto-discovery
• authentication/full-oauth-server.md - Complete built-in OAuth server

Authorization

• authorization.md - Scope-based access control, middleware authorization, patterns

Providers

• providers/local.md - Default provider, decorator-based component registration
• providers/filesystem.md - Load components from Python files on disk
• providers/skills.md - Package and distribute component bundles
• providers/custom.md - Build custom providers for any component source

Version history

v1.0.0 (February 2026)

• Initial release covering FastMCP 3.0 (release candidate)
• 30 reference files across 7 categories
• Complete coverage of tools, resources, context, auth, providers, and features