Developer Tools
Twenty-eight everyday developer helpers in one place (now with subnet/CIDR, chmod, an HTTP/MIME/port reference, robots/sitemap and dummy data): URL, Base64, HTML and Unicode encoding, JSON formatting, CSV and type generation, Unix time, JWT decoder, hashes, UUIDs, regex, text diff, number bases, cron, certificate/CSR and mail header readers, business registration number checks, and a table converter.
Everything runs inside this browser; what you enter is never sent to a server or stored. You can paste tokens and keys with some peace of mind, but on a shared computer close the page when you are done.
Good to know
- Text is always handled as UTF-8 bytes, so Korean and other non-ASCII text survives (Base64, Hex, hashes).
- The JWT decoder does not verify signatures — it only reads the contents. The payload is plain Base64, not encryption, so never put secrets in it.
- Times are shown in both UTC and Korea Standard Time (KST, +9).
- Regular expressions run in a separate worker and are stopped after 1.5 seconds (to guard against runaway patterns).
- MD5 and SHA-1 are for checksums only. Do not use them for security such as password storage.
FAQ
Is the JSON or token I paste sent to a server?
No. Every conversion happens in your browser and nothing is transmitted or stored.
Does it verify JWT signatures?
No. Verification needs the secret key, and asking you to type that into a web page is not safe, so only decoding is offered.
Korean text breaks in Base64.
This tool encodes text as UTF-8 bytes. If another tool used EUC-KR or another encoding, the output will differ.
I cannot tell whether my Unix time is seconds or milliseconds.
The unit is detected from the digit count (10 digits seconds, 13 milliseconds, 16 microseconds). If the result looks wrong, pick the unit yourself.