fastapi-inspector

Structured logging and observability middleware for FastAPI applications.

Documentation · Changelog · Contributing

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Features

• Zero-boilerplate middleware — one line to log every request and response
• Structured events — typed LogEvent objects with method, path, status code, latency, and more
• Pluggable storage — in-memory, JSON file, JSON Lines, or SQLite backends
• Filter pipeline — drop health-check noise, log only errors, or set a minimum latency threshold
• Built-in dashboard — mount an event-inspector UI at any path in your app
• Multiple formatters — plain-text or JSON output
• Python 3.10–3.14 with full CI coverage across all versions

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Install

pip install fastapi-inspector

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Quick start

Basic logging

from fastapi import FastAPI
from fastapi_inspector import ObserverConfig, ObserverMiddleware

app = FastAPI()
app.add_middleware(ObserverMiddleware, config=ObserverConfig())

@app.get("/items")
async def list_items():
    return {"items": ["alpha", "beta", "gamma"]}

Every request is now logged to the console with method, path, status code, and latency.

Persist events and open the dashboard

from fastapi import FastAPI
from fastapi_inspector import ObserverConfig, ObserverMiddleware, build_dashboard_app
from fastapi_inspector.storage import InMemoryEventStore

app = FastAPI()
store = InMemoryEventStore()

app.add_middleware(ObserverMiddleware, config=ObserverConfig(), storage=store)
app.mount("/dashboard", build_dashboard_app(store, title="Observer Dashboard"))

Open http://localhost:8000/dashboard to browse and inspect logged events.

Filter out noise

from fastapi_inspector import ObserverConfig, ObserverMiddleware, only_errors, min_duration_ms

app.add_middleware(
    ObserverMiddleware,
    config=ObserverConfig(handlers=["console"], log_format="json"),
    event_filters=[
        only_errors,           # log 4xx/5xx responses only
        min_duration_ms(50.0), # ignore fast responses
    ],
)

See the examples/ directory for more patterns including SQLite storage and custom filters.

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Storage backends

Backend	Class	Use case
In-memory	InMemoryEventStore	Development, testing
JSON file	JsonFileEventStore	Simple persistence
JSON Lines	JsonLinesEventStore	Append-only log files
SQLite	SQLiteEventStore	Queryable local storage

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Python compatibility

• Supported versions: 3.10, 3.11, 3.12, 3.13, 3.14
• Enforced in CI with a tox matrix across all versions

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Development

Install all dependencies:

pip install -e ".[test,docs,dev]"
pre-commit install

Run tests:

pytest -q
pytest -q --cov=fastapi_inspector --cov-report=term-missing   # with coverage
tox                                                           # full version matrix

Build and preview docs:

mkdocs serve        # http://127.0.0.1:8000
mkdocs build --strict

See CONTRIBUTING.md for the full contribution guide.