Nilguard — Python SDK

Server-side error tracking for ASGI apps (FastAPI, Starlette) and WSGI apps (Flask, Django-WSGI). Mirrors the browser SDK's wire format so the dashboard, ticketing and agent-run pipeline work unchanged.

Install

pip install nilguard

For local development, install the package in editable mode from this directory:

uv pip install -e .

You can also pull it directly as a [tool.uv.sources] path entry from another project during local testing.

Quick start

from fastapi import FastAPI
import nilguard

nilguard.init(
    service="billing-api",                     # human-readable identifier
    framework="fastapi",                       # dashboard renders the right icon
    ingest_key="ng_srv_...",                  # shown once at mint time
    backend_url="https://nilguard.example.com",
    environment="production",
    release="2026-05-23-a1b2c3d",
)

app = FastAPI()
app.add_middleware(nilguard.NilguardASGIMiddleware)

@app.get("/healthy")
async def healthy():
    return {"ok": True}

@app.get("/boom")
async def boom():
    1 / 0   # raises ZeroDivisionError; middleware sends a crash bundle, then re-raises

Try the FastAPI example without installing anything

The examples/fastapi_demo.py script uses PEP 723 inline metadata so uv will install FastAPI + uvicorn + this SDK (via a local path source) for you on first run:

cd examples/python-fastapi
NILGUARD_INGEST_KEY="ng_srv_..." uv run fastapi_demo.py

WSGI / Flask quick start

For synchronous WSGI frameworks, wrap the WSGI app with NilguardWSGIMiddleware as the outermost layer. It behaves identically to the ASGI middleware (clean requests send nothing; unhandled exceptions — including ones raised mid-stream while iterating the response body — send one crash bundle, then re-raise) but uses the synchronous HTTP client.

from flask import Flask
import nilguard

nilguard.init(
    service="billing-api",
    framework="flask",
    ingest_key="ng_srv_...",
    backend_url="https://nilguard.example.com",
    environment="production",
)

app = Flask(__name__)
app.wsgi_app = nilguard.NilguardWSGIMiddleware(app.wsgi_app)

@app.get("/boom")
def boom():
    1 / 0   # middleware sends a crash bundle, then re-raises

A runnable demo lives in examples/python-flask/flask_demo.py (PEP 723 inline-deps, same style as the FastAPI demo):

cd examples/python-flask
NILGUARD_INGEST_KEY="ng_srv_..." uv run flask_demo.py

Manual capture

try:
    risky()
except Exception as exc:
    nilguard.capture_exception(exc, context={"job_id": job.id})
    raise

What gets sent

• Clean requests send nothing. The middleware stays on the request path only long enough to observe exceptions.
• Crash bundle on unhandled exception. Includes a network event describing the inbound request plus a crash object with signal=server_exception and a redacted traceback in metadata.
• Headers, cookies, query values, and anything matching the redaction denylist (authorization|cookie|token|secret|password|session|credential|auth) are scrubbed client-side before the POST. The backend re-applies the same rules — it remains the source of truth.

Auth

All ingest requests carry Authorization: Bearer <ingest_key>. No Origin/CORS dance: the token is the only thing the backend trusts for the server-ingest path.