logger

What it is

@kitr/logger is a small logger with levels, child loggers that carry fields, and two output formats: readable in development, JSON in production. On the server every request gets a child logger with its request id.

Runs on the server and in the browser. For alerts about errors, use monitoring.

Install

kitr add logger

Adds @kitr/logger, its provider and config/logger.ts. server adds it for you. Every change.

Quick start

In a controller, the logger is ctx.logger, a child of the app's logger that adds the request id to every line:

// server/controllers/orders_controller.ts
import type { HttpContext } from '@kitr/api'

export default class OrdersController {
  async ship({ logger, params }: HttpContext<{ id: string }>) {
    logger.info('order shipped', { orderId: params.id })
    return { orderId: params.id, status: 'shipped' }
  }
}

Call POST /api/orders/1042/ship in development and the server prints:

INFO  14:03:22.418 [app] order shipped {"requestId":"9b2f6c1e-4f3a-4c1d-8e7a-2b5d0c9e1f44","orderId":"1042"}

In production, where NODE_ENV=production, the same call writes one JSON object per line, ready for your log service:

{"level":"info","time":"2026-11-07T14:03:22.418Z","name":"app","requestId":"9b2f6c1e-4f3a-4c1d-8e7a-2b5d0c9e1f44","orderId":"1042","msg":"order shipped"}

Keep the message fixed and put the variable parts in fields, so a log service can count every order shipped line. Next in the guide: Write your first log line.

Built on

kitr adds the request-scoped child logger, the pretty format, timing, run-time level changes and the devtools mirror.

Problems it solves

• Unreadable logs in development, unsearchable logs in production. Choose the output format.
• Repeating the same fields on every line. Add fields to every line.
• Lines you cannot tie to a request. Log during a request.
• Errors logged as [object Object]. Log an error.
• Timing by hand. Time an operation.
• Restarting to see debug output. Change the level at run time.

Further reading

• Guide.
• API reference.
• Server.
• Monitoring and Devtools.
• Configuration.