What is Rexact for?
Most regexes found online have never been verified: copied from an upvoted Stack Overflow answer, never run against a real set of cases, never audited for a catastrophic blowup. Rexact actually runs every pattern against your test cases, measures its ReDoS risk, and checks its portability across 7 engines — before you ship it to production.
What Rexact actually checks
Real verification
Every pattern is genuinely run against the examples you provide — never guessed by a language model. You see exactly which cases pass, which fail, and why.
ReDoS analysis
A poorly written regex can lock up an entire server on a single request. Rexact systematically analyzes the risk of catastrophic backtracking and shows a concrete attack string when a pattern is vulnerable — never a complacent "safe".
Cross-engine portability
A "\d" doesn't mean the same thing in JavaScript, Python, and PCRE. Rexact checks your pattern's compatibility across 7 engines (JS, PCRE, Python, RE2, Java, .NET, grep) and points out exactly what differs.
Who it's for
Rexact is for anyone who writes or maintains regexes: developers validating user input, people writing a log filter, or anyone who has ever copied a pattern found online without being sure it actually works.
What Rexact is not
Rexact checks the shape of a piece of data, not its business, legal, or financial validity. A pattern that passes all your tests can still accept an IBAN that doesn't exist or an expired card number — always verify the underlying data itself when it matters.
Free, no account needed
The tester, the ReDoS analysis, and the compatibility check are free, with no account, forever. None of these features sit behind a paywall.