Try browser-native JavaScript regular expressions against your text, inspect matches and captures, and preview replacements in an isolated Worker.
BROWSER-ONLY DEVELOPER TOOL
Test JavaScript regular expressions against text, inspect captures and preview replacements without uploading your input.
01 / PATTERN & INPUT
JavaScript regex only (not PCRE). Enable g to enumerate matches; y is sticky at the current position. Positions are zero-based UTF-16 offsets. Test text is limited to 10,000 characters.
02 / LIVE RESULTS
Patterns and text stay in temporary browser memory. Untrusted regexes run in a disposable Worker with a 1.2-second timeout; no text is uploaded or stored.
Write a regex pattern without / delimiters; this tool uses JavaScript syntax, not PCRE.
Toggle g, i, m, s, u or y and paste text to evaluate locally in a bounded Worker.
Review highlighted matches, capture groups, UTF-16 positions and the replacement preview.
Enter a regex pattern without / delimiters, choose flags, paste test text, and review highlighted matches, positions and capture groups. Add replacement text to preview JavaScript replace behavior.
Live highlighting and match counts, global and sticky flags, named capture groups, replacement previews and a cancellable 1.2-second Worker safety timeout.
Patterns and test text are evaluated in a local browser Worker only. Nothing is uploaded or saved by this tool.
It uses your browser's JavaScript RegExp engine, not PCRE. Some PCRE-specific features and delimiters are not valid JavaScript patterns.
g finds successive matches throughout the test text. y is sticky and requires the next match at the current position; together, gy can find consecutive matches. Without g the tool shows the first matching result.
Yes. Match details show numbered and named capture groups, including groups that did not participate, as well as zero-based UTF-16 start and end positions.
The preview follows JavaScript String.replace rules. Use $&, $1 or $<name> for matched text, numbered groups or named groups; enable g to replace all non-sticky matches.
Patterns run in an isolated Worker with a 1.2-second deadline. If one takes too long the Worker is terminated. Pattern, text, match and output limits also keep rendering manageable.
No. Pattern matching, highlighting and replacement happen in browser memory only. The tool does not upload or persist your pattern or text.