DevMill
Free developer utilities that run entirely in your browser.
Format Converters
Convert and validate JSON, YAML, XML, CSV, TOML and INI without leaving the browser.
Encoders & Hashes
Base64, hex, URL and HTML encoding, JWT decoding and cryptographic hashes.
Generators
UUIDs, fake data, .gitignore files, licenses and config boilerplate.
Diff & Compare
Compare text, JSON and code side by side.
Regex
Test, explain and build regular expressions.
Cron & Schedules
Build and explain cron expressions and see the next run times.
Time Zones
Current UTC offset, DST rules and a converter for every canonical IANA time zone.
Guides
- Validating and formatting JSON in CI and code review
How to catch JSON syntax errors early, read common parser error messages, and use schemas and minification correctly in CI.
- UUIDs and random IDs: v4 vs v7, collision math, and why Math.random is wrong
UUID versions explained, the real collision odds for v4, why Math.random is unsafe for IDs, and how ULID and nanoid compare.
- URL encoding explained: percent-encoding, encodeURIComponent, and + vs %20
How percent-encoding works, reserved vs unreserved characters, encodeURI vs encodeURIComponent, and why double-encoding breaks URLs.
- TOML vs YAML vs JSON vs INI: choosing a config format
A practical comparison of TOML, YAML, JSON and INI for application config, with real examples of where each fits.
- Reading a JWT safely: why decoding is not the same as verifying
JWT structure, base64url decoding, why a decoded token proves nothing, and the alg:none and key-confusion attacks to know about.
- JSON vs YAML: which config format to use, and how to convert safely
How JSON and YAML differ for config files, the Norway problem and indentation traps, and when to convert between them.