# Pagerless for Fastify

> One call registers an onError hook.

URL: https://pagerless.dev/integrations/fastify
Updated: 2026-10-22

## Set up

```bash
npm i pagerless
```

```js
import { pagerlessFastify } from "pagerless/fastify";

pagerlessFastify(app);
```

## What it catches

- 5xx and unknown errors through Fastify's onError hook.
- Reports 5xx and crashes only, never 4xx, and leaves the response, logs and error exactly as they were.
- On Node it also starts the SDK: uncaught errors and unhandled rejections, status and latency per route, failing outbound calls (Stripe, OpenAI, Supabase and others named), a heartbeat every 60 seconds and a deploy marker.

## Questions

### Does it change Fastify's error replies?

No. It only listens; your error handler and replies are unchanged.