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New in version 3.0.0 The Namespace transform prefixes all component names, preventing conflicts when composing multiple servers. Tools and prompts receive an underscore-separated prefix. Resources and templates receive a path-segment prefix in their URIs.
ComponentOriginalWith Namespace("api")
Toolmy_toolapi_my_tool
Promptmy_promptapi_my_prompt
Resourcedata://infodata://api/info
Templatedata://{id}data://api/{id}
The most common use is through the mount() method’s namespace parameter. 
from fastmcp import FastMCP

weather = FastMCP("Weather")
calendar = FastMCP("Calendar")

@weather.tool
def get_data() -> str:
    return "Weather data"

@calendar.tool
def get_data() -> str:
    return "Calendar data"

# Without namespacing, these would conflict
main = FastMCP("Main")
main.mount(weather, namespace="weather")
main.mount(calendar, namespace="calendar")

# Clients see: weather_get_data, calendar_get_data
You can also apply namespacing directly using the Namespace transform. 
from fastmcp import FastMCP
from fastmcp.server.transforms import Namespace

mcp = FastMCP("Server")

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

# Namespace all components
mcp.add_transform(Namespace("api"))

# Tool is now: api_greet