> ## Documentation Index
> Fetch the complete documentation index at: https://gofastmcp.com/llms.txt
> Use this file to discover all available pages before exploring further.
# lifespan
# `fastmcp.server.lifespan`
Composable lifespans for FastMCP servers.
This module provides a `@lifespan` decorator for creating composable server lifespans
that can be combined using the `|` operator.
Example:
```python theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
from fastmcp import FastMCP
from fastmcp.server.lifespan import lifespan
@lifespan
async def db_lifespan(server):
conn = await connect_db()
yield {"db": conn}
await conn.close()
@lifespan
async def cache_lifespan(server):
cache = await connect_cache()
yield {"cache": cache}
await cache.close()
mcp = FastMCP("server", lifespan=db_lifespan | cache_lifespan)
```
To compose with existing `@asynccontextmanager` lifespans, wrap them explicitly:
```python theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
from contextlib import asynccontextmanager
from fastmcp.server.lifespan import lifespan, ContextManagerLifespan
@asynccontextmanager
async def legacy_lifespan(server):
yield {"legacy": True}
@lifespan
async def new_lifespan(server):
yield {"new": True}
# Wrap the legacy lifespan explicitly
combined = ContextManagerLifespan(legacy_lifespan) | new_lifespan
```
## Functions
### `lifespan`
```python theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
lifespan(fn: LifespanFn) -> Lifespan
```
Decorator to create a composable lifespan.
Use this decorator on an async generator function to make it composable
with other lifespans using the `|` operator.
**Args:**
* `fn`: An async generator function that takes a FastMCP server and yields
a dict for the lifespan context.
**Returns:**
* A composable Lifespan wrapper.
## Classes
### `Lifespan`
Composable lifespan wrapper.
Wraps an async generator function and enables composition via the `|` operator.
The wrapped function should yield a dict that becomes part of the lifespan context.
### `ContextManagerLifespan`
Lifespan wrapper for already-wrapped context manager functions.
Use this for functions already decorated with @asynccontextmanager.
### `ComposedLifespan`
Two lifespans composed together.
Enters the left lifespan first, then the right. Exits in reverse order.
Results are shallow-merged into a single dict.