Even though this module is publicly accessible, we do not recommend using it in projects outside of Transloadit. We won't make any guarantees about its workings and can change things at any time, we won't adhere strictly to SemVer.

This module is maintained from a monorepo called monolib.

Overview

@transloadit/sev-logger is a lightweight, printf-style logger with:

• syslog-like levels (EMERG..TRACE) and breadcrumbs
• breadcrumb nesting that auto-pads prefixes so multi-logger output aligns
• structured events (logger.event) alongside formatted lines
• optional timestamps, hostnames, callsites, and clickable paths (each path segment is clickable)
• built-in redaction of secrets (enabled by default)
• ESM/CJS friendly, no runtime deps beyond Node
• Node.js only (browser not supported today)

Install

yarn add @transloadit/sev-logger
# or
npm install @transloadit/sev-logger

Quickstart

import { SevLogger } from '@transloadit/sev-logger'

const log = new SevLogger({ breadcrumbs: ['api'] })
log.info('listening on %s', 'http://localhost:3000')

log.event(SevLogger.LEVEL.NOTICE, {
  event: 'user.login',
  userId: 42,
})

Redaction (on by default)

Secrets are masked before anything is written to stdout/stderr/files. Defaults include:

• Field names: token, secret, password, pass, authorization, auth, api_key, x-api-key, cookie, session, bearer, …
• Patterns: Slack tokens, Bearer/JWT-like strings, AWS AKIA/ASIA keys, 40+ char base64ish strings
• High-entropy fallback for token-like strings
• Works for formatted logs and event() payloads, even when fields are abbreviated.

Repeated references and cycles are preserved (no stack overflows, shared refs stay shared). Non-plain objects such as Date, URL, RegExp, Map, Set, custom classes, and Error/AggregateError causes are retained.

Basic usage (default redaction on):

const log = new SevLogger({ breadcrumbs: ['botty'] })
log.info('token: %s', process.env.SLACK_BOT_TOKEN) // => token: [redacted]
log.event(SevLogger.LEVEL.INFO, {
  event: 'botty.start',
  headers: { Authorization: `Bearer ${process.env.SLACK_BOT_TOKEN}` },
}) // => headers.Authorization: "[redacted]"

Configuration (override defaults):

const log = new SevLogger({
  redact: {
    enabled: true,          // default true
    replacement: '[redacted]',
    keepLast: 4,            // tail to keep visible, default 4
    fields: ['sessionId'],  // extra field names to always mask (case-insensitive)
    patterns: [/SUPERSECRET\w+/g], // extra regexes
    entropy: true,          // mask random high-entropy strings
    custom: [(
      value, path, // path = ['payload', 'headers', 'authorization'] etc.
    ) => (typeof value === 'string' ? value.replace(/abc/g, '***') : value)],
  },
})

// Opt-out completely
const noRedact = new SevLogger({ redact: false })

Events vs formatted lines

• logger.info('File %s', '/tmp/foo') — printf-style with %s/%r/%c for strings/paths/clickables.
• logger.event(level, { event: 'upload.finished', userId, size }) — emits event name + JSON payload (with optional key abbreviations).

Testing

cd packages/sev-logger
yarn test