Awesome Free Online Debugging Tools

A curated list of free, no-signup tools you can use in the browser to debug code, APIs, logs, and web apps. PRs welcome – see Contributing.

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Contents

• Stack Traces & Logs
• API & Webhook Debugging
• JSON / YAML / REGEX
• Format / Minify / Unminify
• SQL
• Time & IDs
• Cookies & Tokens
• Network & Site Health
• Cron Expression Helpers
• Contributing
• License

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Stack Traces & Logs

• Debugly — Free Online Java & Python Stack Trace Formatter & Parser. https://debugly.pages.dev/
• Log Beautify & Formatter — Highlight/clean logs & exceptions. https://freejsonformatter.net/log-formatter.html

API & Webhook Debugging

• Hoppscotch — Browser-based API client. https://hoppscotch.io/
• Webhook.site — Instant unique URL to inspect incoming requests. https://webhook.site/
• RestNinja — Simple online REST client/playground. https://restninja.io/
• curlconverter.com — Turn cURL into Python/JS/Go/etc. https://curlconverter.com/

JSON / YAML / REGEX

• JSONFormatter.org — Format/validate/convert JSON↔CSV/XML/YAML. https://jsonformatter.org/
• jq Playground — Try jq in the browser. https://play.jqlang.org/
• YAML Lint — Validate YAML quickly. https://www.yamllint.com/
• RegExr — Learn, build & test RegEx with cheatsheets. https://regexr.com/

Format / Minify / Unminify

• SQLFormat.org — Browser-based SQL formatter (API available). https://sqlformat.org/
• FreeFormatter XML Formatter — Tidy & view XML. https://www.freeformatter.com/xml-formatter.html
• Minifier.org — Minify JS & CSS online. https://www.minifier.org/
• Unminify.com — Unminify JS/CSS/HTML/XML/JSON. https://unminify.com/
• Diffchecker — Quick text/code diffs. https://www.diffchecker.com/

SQL

• db-fiddle — An online SQL database playground. https://www.db-fiddle.com/
• dalibo-explain — PostgreSQL EXPLAIN visualizer. https://explain.dalibo.com/

Time & IDs

• Epoch Converter — Epoch ↔ human-readable datetime. https://www.epochconverter.com/
• UUIDGenerator.net — Generate UUID v1/v4/v7. https://www.uuidgenerator.net/

Cookies & Tokens

• JWT.io — Decode/verify JWTs (HS/RS/ES), live header/payload. https://jwt.io/

Network & Site Health

• SSL Labs Server Test — Deep TLS/SSL analysis. https://www.ssllabs.com/ssltest/
• Security Headers — Scan & grade HTTP security headers. https://securityheaders.com/
• DNSChecker — DNS propagation checks. https://dnschecker.org/
• PageSpeed Insights — Performance audits & Core Web Vitals. https://pagespeed.web.dev/

Cron Expression Helpers

• crontab.guru — Quick editor & next-run preview. https://crontab.guru/

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Contributing

Spotted a great free, browser-based debugging tool?

1. Add it under the right section with a one-line description.
2. Keep descriptions objective and link to the canonical homepage.
3. Tools must be usable without installing desktop software.

Tip: open issues with tags like tool-idea, bug, broken-link.

License

CC0 – do anything, just keep it useful :)