Upgrading from FastMCP 2

pip install --upgrade fastmcp
# or
uv add --upgrade fastmcp

# Before
mcp = FastMCP("server", host="0.0.0.0", port=8080)
mcp.run()

# After
mcp = FastMCP("server")
mcp.run(transport="http", host="0.0.0.0", port=8080)

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

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

# 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)

# 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")

# Before (v2 accepted this)
@mcp.prompt
def my_prompt():
    return [
        {"role": "user", "content": "Hello"},
        {"role": "assistant", "content": "How can I help?"},
    ]

# After
from fastmcp.prompts import Message

@mcp.prompt
def my_prompt() -> list[Message]:
    return [
        Message("Hello"),
        Message("How can I help?", role="assistant"),
    ]

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

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

await ctx.set_state("client", my_http_client, serializable=False)

from fastmcp import FastMCP
from key_value.aio.stores.memory import MemoryStore

store = MemoryStore()
parent = FastMCP("Parent", session_state_store=store)
child = FastMCP("Child", session_state_store=store)
parent.mount(child, namespace="child")

# Before (v2) — client_id and client_secret loaded automatically
# from FASTMCP_SERVER_AUTH_GITHUB_CLIENT_ID, etc.
auth = GitHubProvider()

# After (v3) — pass values explicitly
import os
from fastmcp.server.auth.providers.github import GitHubProvider

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

# Before
from fastmcp.client.transports import WSTransport
transport = WSTransport("ws://localhost:8000/ws")

# After
from fastmcp.client.transports import StreamableHttpTransport
transport = StreamableHttpTransport("http://localhost:8000/mcp")

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

# After
client = httpx2.AsyncClient(base_url="https://api.example.com", timeout=60)
provider = OpenAPIProvider(spec, client)

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

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

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

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

pip install "fastmcp[tasks]"

# Removed in v4
main.mount(subserver, prefix="api")

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

# Removed in v4
main.import_server(subserver)

# New
main.mount(subserver)

# Removed in 4.0
from fastmcp.server.proxy import FastMCPProxy
from fastmcp.server.openapi import FastMCPOpenAPI

# New
from fastmcp.server.providers.proxy import FastMCPProxy
from fastmcp.server.providers.openapi import OpenAPIProvider

# Removed in 4.0
from fastmcp.server.openapi import FastMCPOpenAPI
server = FastMCPOpenAPI(spec, client)

# New
from fastmcp import FastMCP
from fastmcp.server.providers.openapi import OpenAPIProvider
server = FastMCP("my_api", providers=[OpenAPIProvider(spec, client)])

# Removed in v4
mcp.add_tool_transformation("name", config)

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

# Removed in v4
proxy = FastMCP.as_proxy("http://example.com/mcp")
proxy = FastMCP.as_proxy(backend="http://example.com/mcp")  # keyword form

# New
from fastmcp.server import create_proxy
proxy = create_proxy("http://example.com/mcp")
proxy = create_proxy(target="http://example.com/mcp")  # as_proxy(backend=X) → create_proxy(target=X)

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

# After (removed in 4.0 — use OpenAPIProvider)
from fastmcp import FastMCP
from fastmcp.server.providers.openapi import OpenAPIProvider
server = FastMCP("my_api", providers=[OpenAPIProvider(spec, client)])

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"),
)