Free developer tools calculators — 17+ tools

Developer tools are the small, exact utilities you reach for a dozen times a day: encode a string, format a blob of JSON, test a regex, hash a value, generate a token. Each one does a single job correctly so you don't have to keep a CLI snippet or a sketchy online box bookmarked — and because everything runs in your browser, the data you paste never leaves your machine.

The set covers the jobs that come up most. Base64, URL, and HTML-entity encoders translate text for transport; a JSON formatter and a regex tester debug data and patterns; a hash generator, UUID, and password generator produce identifiers and secrets; and networking tools — an IP subnet calculator, a bandwidth/transfer-time tool, and a cron-expression decoder — round it out.

Each tool follows the governing standard — RFC 4648 for Base64, RFC 3986 for URL percent-encoding, RFC 4122 for UUIDs, CIDR/RFC 4632 for subnets — and the relevant page explains the spec, shows a worked example, and flags the gotchas (URL-safe Base64, why MD5 is fine for checksums but not passwords, the difference between a UUID and a truly random token). Everything is computed locally and updates as you type.