Regex Tester & Debugger
Write a regular expression and see live match highlighting, capture groups, plus replace and split modes. Powered by your browser's native JavaScript engine.
Pattern
Test string
0 charsResult
—Common patterns
Click to loadFrequently asked questions
Which regex flavor is this?
Your browser's ECMAScript engine — the same used by Node.js and modern browsers. Lookbehind, named groups ((?<name>…)), and Unicode property escapes are supported in current engines.
How are capture groups shown?
In Match mode every match lists its numbered and named groups with the captured text and position, so you can verify exactly what each part matched.
Is my text uploaded?
No. Evaluation is entirely local. No pattern or test string leaves your device.
Related tools
About this tool
This free online tool runs entirely in your browser. Your data never leaves your device — there is no server processing, no tracking, and no signup required. Use it as often as you need, on any device.
· Maintained by the Forge Engineering Team
How This Calculator Works
This tool tests regular expressions using the browser's native ECMAScript RegExp engine (ECMA-262 §21.2). JavaScript uses a slightly different regex flavor than PCRE (Perl Compatible Regular Expressions) — for example, JavaScript does not support lookbehind assertions in older engines, named capture groups were added in ES2018, and the s (dotAll) flag in ES2018. All testing is performed client-side.
Frequently Asked Questions
What is the difference between JavaScript and PCRE regex?
JavaScript's RegExp (ECMA-262) lacks some PCRE features: no possessive quantifiers, no atomic groups, and Unicode property classes (\p{...}) require the 'u' flag (ES2018). Lookbehind (?<=...) was added in ES2018 but is not supported in all browsers. Named groups use (?
What do the regex flags mean?
g = global (find all matches, not just the first), i = case-insensitive, m = multiline (^ and $ match line boundaries), s = dotAll (. matches newlines, ES2018), u = unicode (treats patterns as Unicode code points), y = sticky (match from lastIndex only).
How do I capture groups in regex?
Use parentheses to capture: (\d{4}) captures a 4-digit number. Reference captured groups with $1, $2 in replacements or match[1], match[2] in JavaScript. Use (?:...) for non-capturing groups. Named groups (?
Sources & References
Explore more free tools
All calculators are free, private, and work instantly — no signup, no data collection.