Upgrade Guide

Upgrade Guide

Migration instructions for upgrading between FastMCP versions

This guide covers breaking changes and migration steps when upgrading FastMCP.

v3.0.0

Most servers need only one change: update your import from from mcp.server.fastmcp import FastMCP to from fastmcp import FastMCP. The sections below cover less common breaking changes.

Breaking Changes

WSTransport Removed

Use StreamableHttpTransport instead.

Auth Provider Environment Variables Removed

Auth providers no longer auto-load configuration. Read them explicitly:

import os

auth = GitHubProvider(
    client_id=os.environ["GITHUB_CLIENT_ID"],
    client_secret=os.environ["GITHUB_CLIENT_SECRET"],
)

Component enable()/disable() Moved to Server

These methods moved from component objects to the server:

# Before
tool = await server.get_tool("my_tool")
tool.disable()

# After
server.disable(names={"my_tool"}, components=["tool"])

Listing Methods Renamed and Return Lists

get_tools(), get_resources(), get_prompts(), and get_resource_templates() have been replaced by list_tools(), list_resources(), list_prompts(), and list_resource_templates(). The new methods return lists instead of dicts:

# Before
tools = await server.get_tools()
tool = tools["my_tool"]

# After
tools = await server.list_tools()
tool = next((t for t in tools if t.name == "my_tool"), None)

Prompts Use Message Class

Use Message instead of mcp.types.PromptMessage:

# Before
from mcp.types import PromptMessage, TextContent

@mcp.prompt
def my_prompt() -> PromptMessage:
    return PromptMessage(role="user", content=TextContent(type="text", text="Hello"))

# After
from fastmcp.prompts import Message

@mcp.prompt
def my_prompt() -> Message:
    return Message("Hello")

Context State Methods Are Async

ctx.set_state() and ctx.get_state() are now async. State persists across the session:

# Before
ctx.set_state("key", "value")
value = ctx.get_state("key")

# After
await ctx.set_state("key", "value")
value = await ctx.get_state("key")

State Values Must Be Serializable

Session state values must now be JSON-serializable by default (dicts, lists, strings, numbers, etc.), since state is persisted across requests using a pluggable storage backend.

If you need to store non-serializable values (e.g., passing an HTTP client from middleware to a tool), use serializable=False. These values are request-scoped and only available during the current tool call, resource read, or prompt render:

# Middleware sets up a client for the current request
await ctx.set_state("client", my_http_client, serializable=False)

# Tool retrieves it in the same request
client = await ctx.get_state("client")

Server Banner Environment Variable Renamed

FASTMCP_SHOW_CLI_BANNER is now FASTMCP_SHOW_SERVER_BANNER.

OpenAPI timeout Parameter Removed

Configure timeout on the httpx client directly. The client parameter is now optional — when omitted, a default client is created from the spec's servers URL with a 30-second timeout.

# Before
provider = OpenAPIProvider(spec, client, timeout=60)

# After
client = httpx.AsyncClient(base_url="https://api.example.com", timeout=60)
provider = OpenAPIProvider(spec, client)

Metadata Namespace Renamed

The FastMCP metadata namespace changed from _fastmcp to fastmcp, and metadata is now always included. The include_fastmcp_meta parameter has been removed from FastMCP() and to_mcp_tool()—remove any usage of this parameter.

# Before
tags = tool.meta.get("_fastmcp", {}).get("tags", [])

# After
tags = tool.meta.get("fastmcp", {}).get("tags", [])

Behavior Changes

Decorators Return Functions

Decorators now return your original function instead of a component object. This means functions stay callable for testing:

@mcp.tool
def greet(name: str) -> str:
    return f"Hello, {name}!"

greet("World")  # Works! Returns "Hello, World!"

If you relied on the old behavior (treating greet as a FunctionTool), set FASTMCP_DECORATOR_MODE=object for v2 compatibility.

Deprecated Features

These still work but emit warnings. Update when convenient.

mount() prefix → namespace

# Deprecated
main.mount(subserver, prefix="api")

# New
main.mount(subserver, namespace="api")

include_tags/exclude_tags → enable()/disable()

# Deprecated
mcp = FastMCP("server", exclude_tags={"internal"})

# New
mcp = FastMCP("server")
mcp.disable(tags={"internal"})

tool_serializer → ToolResult

Return ToolResult from your tools for explicit serialization control instead of using the tool_serializer parameter.

add_tool_transformation() → add_transform()

# Deprecated
mcp.add_tool_transformation("name", config)

# New
from fastmcp.server.transforms import ToolTransform
mcp.add_transform(ToolTransform({"name": config}))

FastMCP.as_proxy() → create_proxy()

# Deprecated
proxy = FastMCP.as_proxy("http://example.com/mcp")

# New
from fastmcp.server import create_proxy
proxy = create_proxy("http://example.com/mcp")

v2.14.0

OpenAPI Parser Promotion

The experimental OpenAPI parser is now standard. Update imports:

# Before
from fastmcp.experimental.server.openapi import FastMCPOpenAPI

# After
from fastmcp.server.openapi import FastMCPOpenAPI

Removed Deprecated Features

• BearerAuthProvider → use JWTVerifier
• Context.get_http_request() → use get_http_request() from dependencies
• from fastmcp import Image → use from fastmcp.utilities.types import Image
• FastMCP(dependencies=[...]) → use fastmcp.json configuration
• FastMCPProxy(client=...) → use client_factory=lambda: ...
• output_schema=False → use output_schema=None

v2.13.0

OAuth Token Key Management

The OAuth proxy now issues its own JWT tokens. For production, provide explicit keys:

auth = GitHubProvider(
    client_id=os.environ["GITHUB_CLIENT_ID"],
    client_secret=os.environ["GITHUB_CLIENT_SECRET"],
    base_url="https://your-server.com",
    jwt_signing_key=os.environ["JWT_SIGNING_KEY"],
    client_storage=RedisStore(host="redis.example.com"),
)

See OAuth Token Security for details.

Documentation Index

Fetch the complete documentation index at: https://gofastmcp.com/llms.txt Use this file to discover all available pages before exploring further.