fastapi-cache-di¶

Speed up FastAPI startup by caching its dependency-tree introspection.

At startup, FastAPI introspects every route's dependency tree — calling get_typed_signature, get_dependant and get_flat_dependant — with no caching. Dependencies shared across many routes (auth checks, DB handles, role guards …) are re-introspected from scratch for every route. On a large API this dominates import/boot time.

fastapi-cache-di monkeypatches those three functions to memoize their results for the duration of route loading, then restores the originals. The heavy one is get_flat_dependant, called once per route in APIRoute.__init__: caching its recursive results turns O(routes × tree-depth) into O(routes + unique-deps).

Install¶

Install fastapi-cache-di with pip:

pip install fastapi-cache-di

Or add it to your project with uv:

uv add fastapi-cache-di

Quickstart¶

Wrap the code that loads your routes with the context manager:

from fastapi import APIRouter, FastAPI

from fastapi_cache_di import fastapi_deps_cache

app = FastAPI()
users = APIRouter()
orders = APIRouter()
billing = APIRouter()

with fastapi_deps_cache():
    # Registering routes introspects each dependency tree; caching is active here.
    app.include_router(users)
    app.include_router(orders)
    app.include_router(billing)
# originals restored here; cache memory freed

That is all it takes: introspection results are memoized while routes are being registered, and FastAPI's original functions are restored when the block exits.

See the usage guide for manual patching, sharing and inspecting a cache, and thread-safety notes. See how it works for the caching internals, and the API reference for the full public API.

Requirements¶

• Python ≥ 3.12
• FastAPI ≥ 0.112.4

Support¶

This project is hosted on GitHub. Feel free to open an issue if you think you have found a bug or something is missing.

License¶

fastapi-cache-di is licensed under the MIT license.