log-kit overview

log-kit is a structured logger built around three ideas: records are plain JSON, transports are independent, and a failing transport never breaks the host application.

The shape of a logger

import { createLogger } from "@arshad-shah/log-kit";
import { consoleTransport } from "@arshad-shah/log-kit/transports/console";

const log = createLogger({
  level: "info",
  context: { app: "my-service" },
  transports: [consoleTransport({ pretty: process.env.NODE_ENV !== "production" })],
});

log.info("Server started", { port: 3000 });
log.error(new Error("DB connection failed"));

What you get

• Six levels: trace < debug < info < warn < error < fatal, plus "silent" to mute a logger entirely
• Structured records - every log is { timestamp, level, message, context, error? } with optional first-class scope, kind, meta, and args. Plain JSON, transport-friendly
• Child loggers via log.child({ requestId }) for context, or log.child("manifest") for nested string scopes
• log() escape hatch - build a record with full control (meta, kind, args) when wrapping log-kit in a host logger
• Configurable timestamps - ISO string (default), epoch ms, or a custom (date) => string | number
• Perf markers - const ms = log.mark("op")() emits a record with durationMs and returns it
• Runtime transports - addTransport / removeTransport without rebuilding the logger
• Fan-out transports - configure as many as you want; each gets every record above the threshold
• Failure isolation - a transport that throws or rejects never blocks others or surfaces errors to the caller

Why structured

Every record is a plain object with stable keys. Aggregators (Loki, Datadog, OpenSearch) parse them without regex. You can grep them, jq them, ship them to a file. There’s no separate “string template” formatter to bypass when you need machine-readable output later.

What it doesn’t do

• No log sampling (add it via a custom transport if you need it)
• No automatic correlation IDs (use child() and pass IDs explicitly)
• No log redaction (do this in your transport or upstream)
• No ANSI color in production output - JSON only when pretty: false

Composition with other kits

log-kit is a primitive. fetch-kit can take a logger via onError. config-kit can take one via the logger option. Build a logger once at boot and inject it everywhere.