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Regex tester

Processed in this browser

Text limit: 2000000 characters

This tool never uploads your input.

A ticket regex you want to prod before it ships. Python, Go, and grep are different engines. Do not paste a 10 MB log into a greedy `(.*)`.

A validation regex that worked on one email and failed on +tag. This page runs JavaScript RegExp. regex101-class sites let you switch flavors; we do not pretend to be PCRE2.

Literal cleanup is find and replace. Line-unique logs are deduplicator. Cron is not regex — use cron parser.

This browser’s RegExp

A pattern that passes one email and fails +tag addresses. Flavor is JavaScript RegExp, not PCRE2 or Python. Catastrophic backtracking can freeze the tab — keep samples short. Not a WAF.

How to use it

  1. Enter pattern and flags.
  2. Paste a small sample.
  3. Read matches. If the UI stalls, kill the tab and simplify.

Honest limits

Not a WAF. Not Re2 guaranteed linear time. Not a production unit-test runner.

FAQ

Is this PCRE or Python?

JavaScript RegExp in this browser. Named groups and lookbehind depend on the engine version.

Why did the tab freeze?

Catastrophic backtracking. Shorten the haystack or simplify the pattern. We are not a timeout sandbox for production.

Replace as well?

Find-replace may be faster for literal strings. This page is about the pattern.

Multiline / unicode flags?

Use the flags the form exposes (g, i, m, s, u, y as available).

Is the log uploaded?

No. Still do not paste production PII into random testers; this one stays local.

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