---
title: Logging
description: Structured logging that works everywhere the code runs.
type: reference
---

# Logging



```ts
import { log } from '@kreogen/observability/log';

log.info('Subscription created', { userId, plan });
log.warn('Retrying webhook', { attempt });
log.error('Payment failed', { customerId, reason });
```

Four levels — `debug`, `info`, `warn`, `error` — each taking a message and an
optional object of structured fields.

## Output

In development, output is human-readable. In production it is one JSON object
per line:

```json
{"level":"info","time":"2026-01-01T12:00:00.000Z","message":"Subscription created","userId":"usr_123","plan":"pro"}
```

That shape is deliberate. Containers hand stdout straight to whatever
collector the platform runs — Loki, Vector, CloudWatch — so JSON on stdout is
already the transport. A logging library with its own transport would add a
hop that nothing reads.

## Why there is no logging dependency

The logger is dependency-free because `parseError` uses it, and `parseError`
runs in server components, route handlers and the browser alike. Anything this
module imports is traced into client bundles, so a Node-only logging library
would either bloat them or fail outright.

If a project needs richer server-side logging, add it in server-only code
rather than here.

## What to log

Log decisions and outcomes, not control flow. A useful line answers "what
happened, to whom, and why" without needing the surrounding code.

Never log secrets, tokens, passwords or full request bodies. Structured fields
make redaction the default: log an identifier rather than an object.


---

For a semantic overview of all documentation, see [/sitemap.md](/sitemap.md)

For an index of all available documentation, see [/llms.txt](/llms.txt)