Regex Tester
Type a pattern, paste your text, and see every match — with groups and flags explained.
g — find every match, not just the first.
The pattern is JavaScript — no slashes needed. The sample shows named groups in action.
01 Capability
What it does
Small details that make the job quicker.
- Matches highlight live in your text as you type, with zero-width matches marked instead of silently skipped.
- Every match lists its numbered and named capture groups, so you can see exactly what a group caught.
- Flags g, i, m, s and u are plain toggles, each labelled with what it changes.
- Copy the whole match set as clean JSON, ready for a script, a test fixture or a spreadsheet.
- Human errors explain an unterminated group, a stray quantifier or an unfinished character class.
- Runs on the browser's own RegExp engine with no upload, no account and no external request.
02 Questions
Questions
Short answers, no small print.
Is this JavaScript regular expression syntax?
Yes. The pattern is compiled with the browser's own RegExp engine, so lookahead, lookbehind, named groups and Unicode property escapes work where the browser supports them. Write the pattern without the surrounding slashes; use the flag buttons instead.
Why does my pattern match more text than I expected?
Quantifiers such as * and + are greedy by default: they take as much as they can and then give back only what the rest of the pattern needs. Add ? after a quantifier to make it lazy, anchor the pattern with ^ and $, or use a narrower character class. The highlighted matches show exactly what was taken.
What do the flags do?
g finds every match instead of stopping at the first. i ignores case. m makes ^ and $ match the start and end of each line. s lets . match a newline. u turns on Unicode mode, which changes how escapes such as \p{L} are read. Turn g off when you only want the first match.
Why is a group shown as undefined or missing?
The group is optional and did not take part in that match — for example, the (s)? in /cat(s)?/ when the text says cat. That is normal. The tool leaves the group out of the JSON rather than pretending it matched an empty string.
Can I test a pattern against a very large document?
Up to 100,000 characters. Beyond that the tool asks you to shorten the text rather than freezing the tab. It also stops collecting after 2,000 matches and says so; copying includes the matches it found.
Is my pattern or text sent anywhere?
No. Compiling, matching and highlighting all happen in this browser tab. There is no upload, account, logging or external request, and both fields disappear when you close the page.