fastapi-lens 0.2.0

API usage intelligence for FastAPI — track, analyze, and surface dead endpoints.

fastapi-lens 🔍

API usage intelligence for FastAPI — lightweight middleware that tells you which endpoints are thriving, which are cold, and which are dead. Now with a Premium HTML Dashboard.

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Why fastapi-lens?

You build APIs. Over time, routes accumulate. Some are called thousands of times a day. Others haven't been touched in months. You don't know which is which — until now.

fastapi-lens is a zero-infrastructure solution: no Datadog, no Prometheus, no external services. Just a SQLite file, a JSON API, and a beautiful real-time dashboard.

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New in v0.2.0: The Lens Dashboard 📊

Visualizing your API health has never been easier. fastapi-lens now includes a built-in, premium HTML dashboard with:

• Real-time Metrics: Traffic, success rates, and active route counts.
• Advanced Latency: P50, P95, and P99 percentiles for every endpoint.
• Health Indicators: Visual badges for active, cold, and dead routes.
• Error Tracking: Visual breakdown of 4xx and 5xx errors per endpoint.

Access it at: /lens/dashboard

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Installation

pip install fastapi-lens

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Quickstart

from fastapi import FastAPI
from fastapi_lens import LensMiddleware, LensConfig

app = FastAPI()

app.add_middleware(
    LensMiddleware,
    config=LensConfig(
        security_enabled=True,         # Protects dashboard and API
        report_key="your-secret-key",  # Your access key
        db_path="lens.db",             # SQLite file path
    ),
)

@app.get("/items")
def list_items():
    return [{"id": 1}]

Accessing your Data

• Dashboard: http://localhost:8000/lens/dashboard?report_key=your-secret-key
• JSON API: GET /lens/report with header X-Lens-Key: your-secret-key (or query param ?report_key=...)

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Report endpoints

Endpoint	Description
GET /lens/dashboard	The Visual Dashboard (SPA)
GET /lens/report	Full JSON report — all endpoints with advanced metrics
GET /lens/report/top	Most called endpoints in the current window
GET /lens/report/dead	Endpoints with no calls in 30+ days

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Advanced Metrics

Unlike basic loggers, fastapi-lens provides real performance insights:

• Percentiles: Accurate P50, P95, and P99 latency tracking.
• Error Segregation: Count 4xx and 5xx errors separately to distinguish between client and server issues.
• Success Rate: Automatic percentage calculation based on non-5xx responses.

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Configuration

LensConfig(
    db_path="lens.db",           # SQLite path. Use ":memory:" for tests
    security_enabled=False,      # Use True to require report_key
    report_key="lens-secret",    # The key used for Auth
    report_path="/lens/report",  # Customize the API path
    ignore_unmapped=True,        # Ignore requests to routes not in your app
    exclude_paths={              # Always excluded from tracking
        "/lens/report", "/lens/dashboard", "/docs", "/favicon.ico"
    },
    exclude_methods={"HEAD", "OPTIONS"},
    flush_interval=5.0,          # Seconds between batch writes
    max_batch_size=100,          # Flush early if queue exceeds this
    dead_threshold_days=30,      # Days without calls = "dead"
    cold_threshold_days=7,       # Days without calls = "cold"
)

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Architecture

Your FastAPI app
│
├── LensMiddleware (Starlette BaseHTTPMiddleware)
│   ├── Intercepts every request (non-blocking)
│   ├── Resolves route template  (/users/42 → /users/{user_id})
│   ├── Pushes to asyncio.Queue  (never slows the request)
│   └── Background task flushes queue → SQLiteStorage (WAL mode)
│
└── /lens/dashboard  (The Premium UI)
└── /lens/report     (JSON APIRouter)

Design principles:

• Non-blocking: the request path only does a queue.put_nowait().
• Batch writes: SQLite writes are asynchronous and batched.
• Noise Reduction: Automatically filters common noise (favicon, robots.txt) and unmapped paths.
• Zero mandatory deps: only uses FastAPI/Starlette built-ins.

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Contributing

Contributions are welcome! Please see CONTRIBUTING.md for local setup and testing guidelines.

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License

MIT