Interactive Regex Builder & Tester
Build a sequence from escaped literal text, digits, ASCII letters or whitespace and bounded repetitions; the pattern remains editable. Matching uses only this browser’s JavaScript RegExp, with g/i/m/s/u flags, not PCRE or another engine. A local worker has an approximate one-second cancellation budget including startup. Input and time limits do not detect or guarantee freedom from catastrophic backtracking; no performance or pattern-safety claim is made. No upload.
A QUICK WALKTHROUGH
How to use this tool
- Build or enter a pattern, then test it.
- Append token
- Run JavaScript match
JavaScript pattern (no / delimiters)
Build a sequence from escaped literal text, digits, ASCII letters or whitespace and bounded repetitions; the pattern remains editable. Matching uses only this browser’s JavaScript RegExp, with g/i/m/s/u flags, not PCRE or another engine. A local worker has an approximate one-second cancellation budget including startup. Input and time limits do not detect or guarantee freedom from catastrophic backtracking; no performance or pattern-safety claim is made. No upload.
Displayed matches
Up to 200 matches; each match display is capped at 1,000 UTF-16 characters and the first 20 numbered groups at 500 each. Non-global mode shows one match. Unsupported syntax is an engine error. Results use text nodes; patterns and test text are never executed as HTML.
GOOD TO KNOW
Common questions
Does this use PCRE?
No. Matching uses the browser's JavaScript RegExp engine and its supported flags; PCRE syntax and features are not provided.
Does the time limit guarantee a safe pattern?
No. The worker can be cancelled after about one second, but this does not detect or guarantee freedom from catastrophic backtracking.