Regular Expression Tester
Check a JavaScript regular expression against sample text.
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Find global matches using JavaScript regular-expression syntax, with optional case-insensitive, multiline, dotAll and Unicode flags. Matching runs in a short-lived worker so a slow pattern cannot freeze the page. Enter a pattern without surrounding slashes and paste sample text. Global matching is always on; choose i (ignore case), m (line anchors), s (dot matches newlines) or u (Unicode mode). The result shows up to 100 matches, capture groups and UTF-16 offsets. Patterns run in a worker with a time limit. Only the first 100 matches are shown. Matching has a short time limit and sample text is limited to 100,000 characters. Offsets are JavaScript UTF-16 indices; regex syntax differs across engines.
Regular expression (no surrounding slashes)
\b[A-Z][a-z]+\b
Sample text
Ada and Sam buy tea.
Expected output
Flags: gu Matches: 2 1. "Ada" (UTF-16 index 0) 2. "Sam" (UTF-16 index 8)
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Quick answer
Find global matches using JavaScript regular-expression syntax, with optional case-insensitive, multiline, dotAll and Unicode flags. Matching runs in a short-lived worker so a slow pattern cannot freeze the page.
The page and its assets load from the site; this operation uses your entered values only in this browser and does not send them to a calculation endpoint.
How to use it
Enter a pattern without surrounding slashes and paste sample text. Global matching is always on; choose i (ignore case), m (line anchors), s (dot matches newlines) or u (Unicode mode). The result shows up to 100 matches, capture groups and UTF-16 offsets. Patterns run in a worker with a time limit.
Limits
Only the first 100 matches are shown. Matching has a short time limit and sample text is limited to 100,000 characters. Offsets are JavaScript UTF-16 indices; regex syntax differs across engines.
Frequently asked questions
Which flags can I use?
Global matching is always enabled. Optional flags are i for case-insensitive matching, m for line anchors, s for dot matching line breaks, and u for Unicode behavior.
Why did the pattern stop or show only some matches?
Patterns run in a separate worker with a 1.5-second limit, and only the first 100 matches are returned. Offsets count UTF-16 code units, as JavaScript string indices do.
Sources and references
These references document the cited standard or browser API; they do not validate the tool’s output.