Test JavaScript regular expressions in the browser, see matches, groups, flags, and errors without sending text to the server.
The regex tester compiles regular expressions with browser JavaScript RegExp and shows matches, captured groups, named groups, selected flags, optional indices, and engine error messages.
Type the pattern without delimiters, paste test text, adjust flags, and inspect the match list. Shared links preserve only flags and limit by default; include content only when it can become public.
The pattern and text are processed in the browser. The live link stores only flags and match limit.
Type without /.../ delimiters. If you paste a JavaScript literal, use the parse-literal button.
Choose JavaScript flags and how many matches to collect before truncating results.
The limit avoids huge lists and reduces freeze risk.
Paste a sample small enough to test safely.
0 characters, 0 UTF-16 indices, 0 lines.
By default, the link stores only flags and limit. Pattern and text enter the # fragment only when you allow it.
The current link does not include pattern or text.
Exposes match and group indices when the browser supports it.
Finds all matches instead of stopping at the first one.
Ignores uppercase and lowercase differences.
Makes ^ and $ consider the start and end of each line.
Lets . also match line breaks.
Enables classic JavaScript Unicode behavior.
Enables modern Unicode sets when the browser supports them.
Matches only from the current last index.
Numbered groups appear in parenthesis order. Named groups use JavaScript named-capture syntax and appear in a separate table.
This tester uses browser RegExp. PCRE, Python, Ruby, PHP, and .NET may handle syntax and Unicode differently.
Some expressions can trigger expensive backtracking. The heuristic warning helps, but does not prove a regex is safe.
No. Compilation and matching run in the browser. Content enters the link only if you enable pattern and text sharing.
It uses the JavaScript RegExp engine available in the current browser.
The interface offers g, i, m, s, u, v, y, and d. The u and v flags are exclusive, and newer flags depend on browser support.
Open the match list. Numbered and named groups appear below each match; with d, indices also appear when supported.
Different engines support different features. This page shows JavaScript behavior, not PCRE or another engine.
Yes. Some backtracking patterns on large inputs can freeze a tab. Use small samples and treat warnings as attention signals.
Yes, but only by enabling content inclusion. The pattern and text stay in the link fragment and are visible to whoever receives the URL.