Regex Builder and Explain
Build a real ECMAScript pattern, inspect its syntax tree and test locally in a cancellable Worker.
Enabling local controls…
Pattern and syntax report
Build or explain a pattern to see native syntax and match tables. No pasted HTML is rendered.
Model and limits
ECMAScript gim flags. Classes form a union; dot must stand alone. A raw fragment is grouped when it supplies the atom, otherwise appended after the quantified class; OR is grouped before the chosen wrapper and outer anchors. Templates are scoped examples, not complete validators. Static AST hints cannot prove safety or runtime complexity; matching has a 1s Worker deadline, startup10s, pattern4000/text100000 UTF-16 units,250 matches/250 explanation rows and1MiB complete export. Editing cancels and clears stale results; no network or input execution beyond the requested regex match.
ECMAScript regular expressions ↗regexpp parser ↗ToolHubEN inspected controls ↗
How to use this tool
Choose a character union and one quantifier, add grouping/anchors or a raw fragment, then build and test. Templates and searchable syntax notes are available; Explain accepts an edited pattern.
When not to use it
ECMAScript gim flags. Classes form a union; dot must stand alone. A raw fragment is grouped when it supplies the atom, otherwise appended after the quantified class; OR is grouped before the chosen wrapper and outer anchors. Templates are scoped examples, not complete validators. Static AST hints cannot prove safety or runtime complexity; matching has a 1s Worker deadline, startup10s, pattern4000/text100000 UTF-16 units,250 matches/250 explanation rows and1MiB complete export. Editing cancels and clears stale results; no network or input execution beyond the requested regex match.