Two things always bothered me about the usual "paste your JSON here" websites: half of them quietly upload your data to a server, and the other half drown you in ads. When you are pasting an access token into a JWT decoder, "where does this data actually go?" is not a paranoid question.
So we built a collection of developer tools where everything runs in your browser. No account, no uploads, no server round-trips — the parsing happens in JavaScript on your own machine. Here are the ten I reach for most often.
1. JSON Formatter
https://hysenlabs.com/tools/json-formatter
Formats, validates and minifies JSON. The error message points at the exact character that broke your config, which is the difference between 30 seconds and five minutes of staring at a bracket.
2. JWT Decoder
https://hysenlabs.com/tools/jwt-decoder
Decodes the header and payload instantly and flags expiration. Handy when debugging auth flows — and since the token never leaves your machine, it stays safe to use with real tokens.
3. Cron Parser
https://hysenlabs.com/tools/cron-parser
Explains any cron expression in plain English ("at 03:00, every 5 days") and shows the next scheduled runs. I no longer pretend to remember what */15 2-6 * * 1-5 means.
4. Regex Tester
https://hysenlabs.com/tools/regex-tester
Live highlighting of matches as you type, including capture groups. Test patterns against your real sample data locally, not through someone else's API rate limit.
5. SQL Formatter
https://hysenlabs.com/tools/sql-formatter
Turns the 200-character one-liner from your ORM logs into something a human can read during code review. Supports multiple SQL dialects.
6. UUID Generator
https://hysenlabs.com/tools/uuid-generator
Bulk v4 UUIDs in one click, with a "copy all" button. Works offline.
7. Hash Generator
https://hysenlabs.com/tools/hash-generator
MD5, SHA-1, SHA-256 and SHA-512 from text or a file. Useful for checksums and cache keys without dropping into a shell.
8. Base64
https://hysenlabs.com/tools/base64
Encodes and decodes text and files, including the URL-safe variant that trips people up constantly when working with JWTs.
9. Diff Checker
https://hysenlabs.com/tools/diff-checker
Side-by-side text diff with changed lines highlighted. Paste two versions of a config file and see exactly what moved.
10. Timestamp Converter
https://hysenlabs.com/tools/timestamp-converter
Unix timestamps to human-readable time and back, timezone aware. Debugging a 1700000000 in a log line? Paste, done.
The rest of the set
The full collection currently has 35 tools — URL parser, user-agent parser, HTML entity encoder, color converter, CSV to Markdown, AES encryption, HMAC generator and more. All free, all client-side:
One more thing
The same site publishes a weekly GitHub star-growth ranking with an open methodology and a downloadable dataset, if you like tracking which open-source projects are genuinely trending rather than just loud on social media:
https://hysenlabs.com/data/star-growth
Everything runs client-side, so paste away — your data stays in your browser tab. If you have ideas for tools worth adding, the feedback link on the site works and we actually read it.
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