Test JavaScript regular expressions locally. Highlight matches, inspect numbered and named capture groups, and export a match report without uploading your text.
\d digit · \w word character · \s whitespace · + one or more · * zero or more · ^/$ anchors · (…) numbered capture · (?<name>…) named capture.
This uses your browser’s JavaScript RegExp engine, not PCRE or Python syntax. The g flag finds successive non-overlapping matches. Expressions run only after you select Test expression. Complex patterns can time out; no partial report is exported on errors.
JavaScript match and capture reference ↗Your patterns and test text stay on your device. Testing happens in a disposable browser worker with no uploads, saved input history or account. Match highlights are safe text nodes, never rendered HTML. Cancel, edits and page exit terminate pending work.
This tool uses the JavaScript RegExp engine built into your browser. It supports the g, i, m, s and u flags. Syntax availability depends on your browser. PCRE, Python, Java and other engines may behave differently. Enter pattern text directly, without / delimiters; backslashes do not need JavaScript string escaping.
g finds successive non-overlapping matches; without it only the first match is returned. i ignores case, m changes line-anchor behavior, s lets dot match line terminators, and u enables Unicode-aware matching. Sticky matching, Unicode sets and capture index flags are not exposed in this version.
Each match reports its value, zero-based start index and exclusive end, and one-based line and column. All positions use UTF-16 units, so emoji can take two units. Browser textarea line endings normalize to LF; line counting also recognizes Unicode line and paragraph separators. Numbered captures appear in order, named captures under groups. An unmatched capture is null while a matched empty string is "". Capture values, not separate capture positions, are reported.
Zero-length matches appear as vertical markers in the preview. Global matching advances one Unicode code point with u, otherwise one UTF-16 unit, after an empty match. No matches produces an empty matches array, which can still be exported. Results show at most 500 matches. If another match exists, limited is true and the total is not calculated. Capture data is bounded to 400,000 compact JSON units; larger reports fail without partial exports.
Expressions run in a worker rather than on the page thread. A three-second deadline includes worker startup; Cancel, edits or page exit terminate the worker. Errors and timeouts clear prior results and expose no partial output. Input is limited to 100,000 UTF-16 text units and 2,000 pattern units.
Nothing is uploaded or stored by this tool. The JSON report contains the pattern, flags, matched text and captures, so it may contain sensitive portions of your input. Review before sharing it. Unmatched source text is not included in the report, though it remains visible in the local highlighted preview. Text and markup are never executed.
