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debug is a lightweight JavaScript logging utility that enables selective, namespaced debug output in Node.js and browsers via environment variables. Developers toggle debug namespaces on/off without code changes, making it ideal for development-time diagnostics.
Key facts
Objective fields from the source. Values we can't verify are shown as “Unknown” rather than guessed.
| Field | Value |
|---|---|
| Repository | debug-js/debug |
| Owner | debug-js |
| Primary language | JavaScript |
| License | MIT — OSI-approved |
| Stars | 11.4k |
| Forks | 984 |
| Open issues | 87 |
| Latest release | 4.4.3 (2025-09-13) |
| Last updated | 2026-04-01 |
| Source | https://github.com/debug-js/debug |
What debug is
A minimal Printf-style formatter wrapping console.error, supporting namespace filtering, colored TTY output, millisecond deltas, and localStorage persistence in browsers. Works in Node.js and modern web browsers with built-in formatters (%s, %d, %o, %O, %j) and custom formatter extension.
Get the debug source
Clone the repository and explore it locally.
git clone https://github.com/debug-js/debug.gitcd debug# follow the project's README for install & configurationNeed it deployed, integrated, or customized instead? DEV.co ships production installs.
Best use cases
Implementation considerations
- Namespace conventions should follow 'library:feature' pattern to avoid collisions and enable wildcard filtering.
- Install optional 'supports-color' module alongside debug to enable full TTY color palette; otherwise limited to basic colors.
- DEBUG environment variable filtering supports wildcards (*) and exclusion (-); document expected namespaces for teams.
- In non-TTY contexts (CI/logs), output defaults to ISO timestamps; consider DEBUG_COLORS and DEBUG_DEPTH tuning.
- Custom formatters extend debug.formatters; ensure they do not throw or block the event loop in high-frequency logging.
When to avoid it — and what to weigh
- Production logging required — Not designed for structured logging, persistence, or alerting. Use Winston, Pino, or Bunyan for production observability.
- High-volume log ingestion needed — No built-in log aggregation, filtering, or sampling. Stderr-based output unsuitable for log shippers at scale.
- Security-sensitive contexts — Environment variable control means debug output could leak secrets if DEBUG env var is misconfigured or overridden in production.
- Custom serialization or context tracking — No async context propagation, request tracing, or metadata binding. Primitives only (namespace + message + formatters).
License & commercial use
MIT License. Permissive OSI license permitting commercial use, modification, and distribution with attribution. No warranty.
MIT license explicitly permits commercial use, including proprietary software. No restrictions on closed-source or SaaS deployments. Requires retention of license notice and copyright.
DEV.co evaluation signals
Editorial assessment — not user reviews. Directional, with an explicit confidence level.
| Signal | Assessment |
|---|---|
| Maintenance | Active |
| Documentation | Strong |
| License clarity | Clear |
| Deployment complexity | Low |
| DEV.co fit | Good |
| Assessment confidence | High |
No inherent security vulnerabilities documented in README. Risk: DEBUG env var controls output—if set to '*' in production, may expose sensitive data (secrets, API keys) in logs. Ensure env var isolation between dev and prod. No validation/sanitization of format strings; malformed %o on circular refs returns '[Circular]'—safe but verify in security-critical contexts.
Alternatives to consider
Winston
Full-featured logging framework with transport layers, structured logging, and production-grade log aggregation. Heavier footprint; better for enterprise/SaaS.
Pino
High-performance JSON logging for Node.js with async context, child loggers, and log streaming. Stricter structure; less suitable for ad-hoc debugging.
console.log with conditional checks
Zero dependencies; requires manual if(DEBUG) guards in code. No filtering, no formatting, no localStorage in browsers. Suitable only for trivial cases.
Build on debug with DEV.co software developers
Integrate debug into your Node.js or browser app in minutes. Or contact our team to discuss structured logging for production systems.
Talk to DEV.coRelated open-source tools
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debug FAQ
Can I use debug in production?
Does debug support log levels (info, warn, error)?
How do I use debug in the browser?
Can I extend debug formatters?
From evaluation to production software
Bringing debug into production usually means new services, new interfaces, and new failure modes. DEV.co is a software development agency that builds all three and stays on for the open-source observability maintenance.
Ready to streamline your development debugging?
Integrate debug into your Node.js or browser app in minutes. Or contact our team to discuss structured logging for production systems.