Base64
Text is encoded as UTF-8 first, so non-ASCII survives the round trip.
JWT decoder
This decodes only. Verifying the signature needs the issuer's key, so a token that decodes cleanly here still proves nothing about who issued it.
UUID
Version 4, from crypto.getRandomValues — the browser's
cryptographic random source, not Math.random.
Hashes
SHA-1 is here because you will meet it in old systems; do not pick it for anything new. MD5 is missing because the browser's crypto API refuses to implement it, which is a fair position.
Regex tester
Cron parser
Times are shown in your local zone. When both day-of-month and day-of-week are restricted, cron fires when either matches — a rule that surprises people often enough to be worth stating.