@padmaj/logfmt

Serialize objects to logfmt key=value format and parse them back. Zero dependencies. TypeScript-first. Works in Node and browser.

Compatible with Datadog, Grafana, Heroku, and any log aggregator that speaks logfmt.

Install

npm install @padmaj/logfmt

Usage

Serialize → logfmt string

import { logfmt } from '@padmaj/logfmt'

logfmt({ level: 'info', msg: 'server started', port: 3000 })
// → 'level=info msg="server started" port=3000'

logfmt({ level: 'error', ok: false, latency: 1.5 })
// → 'level=error ok=false latency=1.5'

Parse logfmt string → object

import { parseLogfmt } from '@padmaj/logfmt'

parseLogfmt('level=info msg="server started" port=3000')
// → { level: 'info', msg: 'server started', port: '3000' }

Use with console.log

console.log(logfmt({ level: 'info', msg: 'request received', path: '/api/users', ms: 42 }))
// level=info msg="request received" path=/api/users ms=42

Serialization rules

| Value type | Example input | Output | |---|---|---| | Plain string | 'info' | level=info | | String with spaces | 'server started' | msg="server started" | | String with = | 'a=b' | expr="a=b" | | Number | 3000 | port=3000 | | Boolean | true | ok=true | | null | null | err (bare key) | | undefined | undefined | (omitted) |

API

logfmt(obj: Record<string, string | number | boolean | null | undefined>): string

Serializes an object to a logfmt string.

parseLogfmt(line: string): Record<string, string>

Parses a logfmt string back into an object. All values are returned as strings.

Notes

• logfmt and parseLogfmt are round-trip compatible — parsing a serialized string returns the original values (as strings).
• Keys with undefined values are omitted from output.
• Keys with null values are rendered as bare keys (no =value).
• Keys must not contain spaces, =, or " — logfmt throws if they do.
• parseLogfmt rejects inputs longer than 10,000 characters with a RangeError.

License

MIT