reqly 0.1.3

Auto-instrumentation SDK for FastAPI and Flask: zero-code latency, error rates, and status codes shipped to a Reqly collector.

reqly

Open-source API observability SDK for FastAPI and Flask.
Auto-instrument your app with 2 lines of code — get latency percentiles, error rates, status distribution, top routes, and weekly AI-generated anomaly reports.

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Install

pip install reqly

Usage

FastAPI

import reqly
from fastapi import FastAPI

app = FastAPI()
reqly.instrument(app, service_name="checkout-api")
# Every route is now tracked — latency · error rate · status codes

Flask

import reqly
from flask import Flask

app = Flask(__name__)
reqly.instrument(app, service_name="checkout-api")

instrument() auto-detects FastAPI vs Flask — no other code changes needed.

What you get

• p50 / p95 / p99 latency per route
• Error rates and status code distribution (2xx / 3xx / 4xx / 5xx)
• Top routes ranked by volume and error rate
• Live requests/min tile, time windows 1h / 6h / 24h / 7d
• Weekly AI anomaly report — z-score detection with Groq (Llama 3.3-70b) writing the narrative

"Your /auth endpoint degrades every Monday morning (08:00–10:00), with error rate at 18% vs. a 2% baseline and p95 latency at 1850ms vs. 320ms baseline."

Live Demo

Reqly is running live against EventFlow, a Flask event management app.

• Demo app → eventflow-g2h5.onrender.com
• Metrics dashboard → reqly-eventflow-dashboard.onrender.com

Login as Administrator ([e-mail] / Admin@123) → click Metrics in the nav.

Configuration

Every option can be passed as a kwarg to instrument() or set via environment variable.
Resolution order: kwarg → env var → default.

kwarg	env var	default
service_name	REQLY_SERVICE_NAME	sys.argv[0] basename
collector_url	REQLY_COLLECTOR_URL	http://localhost:8000
api_key	REQLY_API_KEY	None
sample_rate	REQLY_SAMPLE_RATE	1.0
flush_interval_seconds	REQLY_FLUSH_INTERVAL_SECONDS	5.0
max_batch_size	REQLY_MAX_BATCH_SIZE	200
max_queue_size	REQLY_MAX_QUEUE_SIZE	2000
ignore_routes	REQLY_IGNORE_ROUTES (comma-separated)	/health,/metrics
capture_request_body	REQLY_CAPTURE_REQUEST_BODY	False

Design guarantees

Fail-open — any internal SDK error is caught and logged once; instrumentation disables itself rather than raise into your app. A slow or unreachable collector never blocks request threads — all shipping happens on a background thread with strict HTTP timeouts.

Bounded cardinality — routes are captured as the framework's matched template (/users/{id}), never the raw path (/users/123). Unmatched paths collapse into a single __unmatched__ bucket.

Bounded memory — events are held in a fixed-size in-memory queue; under backpressure, oldest events are dropped and counted rather than growing unbounded.

Self-hosting

Reqly is fully self-hostable. Run the full stack (collector + TimescaleDB + dashboard) with Docker Compose:

git clone https://github.com/tanisheesh/reqly.git
cd reqly
docker compose up -d

See the repository and CONTRIBUTING.md for full setup instructions.

License

GPL-3.0-or-later — see LICENSE.