Test a JavaScript regular expression against sample text in your browser. Enter a pattern and flags, then review match positions and capture groups. Pattern execution runs in a short-lived worker that is stopped after two seconds; neither pattern nor text is uploaded.
JavaScript regex tester
Example: (?<word>[A-Z][a-z]+). JavaScript regular expression syntax is used.
Optional JavaScript flags such as g (all matches), i (ignore case), and m (multiline). The browser reports unsupported or repeated flags.
Choose Test to run this pattern on the sample text.
How are matches reported?
Enter the pattern without its surrounding slash characters. The tool passes the pattern and flags to the browser's JavaScript RegExp implementation. With the g flag it lists each match, its zero-based UTF-16 start and end offsets, matched text, and numbered capture groups. Without g, it shows the first match. Offsets refer to JavaScript string positions, not grapheme clusters or line numbers.
Pattern execution is isolated in a browser worker and stopped after two seconds. Text is limited to 20,000 characters and patterns to 500 characters. A timeout does not prove that a pattern is invalid; simplify it or test smaller input. The browser's regex syntax and supported features apply, so results may differ from other languages or tools.
Frequently asked questions
Does this support PCRE, Python, or other regex dialects?
No. It uses the JavaScript regular-expression implementation in your browser. Other engines can support different syntax, flags, and behavior.
Why do I only see one result?
Add the g flag to find all non-overlapping matches. Without it, JavaScript returns the first match. The y sticky flag also restricts matching to the current position.
Can I use this to prove a pattern is safe or fast?
No. A successful sample test does not prove correctness for other input. The worker timeout limits how long this page waits, but this tool is not a security or performance audit.
Does the page send or save my pattern or text?
No. The pattern and sample are passed to a temporary worker in the same browser page. The worker is terminated after each test or timeout; this page does not submit the text to a service or save it in browser storage.
What demand evidence supports this tool?
On November 5, 2026, seodata.dev's US keyword report showed 33,100 average monthly searches for “regex tester,” based on Google Ads API data. The report was updated July 14, 2026. This third-party estimate is several months old and is not this site's traffic or a forecast.
Sources · checked November 5, 2026
Related: format JSON, convert CSV to JSON, and check a limited MCP configuration structure.
Methodology and limitations
This browser-only tester passes a user-supplied pattern, flags, and text to the browser's JavaScript RegExp implementation inside a temporary web worker. It lists at most 500 matches with zero-based UTF-16 start and end offsets and numbered captures; the worker is terminated after two seconds. Pattern and input limits are 500 and 20,000 characters. It does not support other regex dialects or assess correctness, security, or performance. seodata.dev reported 33,100 average monthly US searches for “regex tester” from Google Ads API data; its report was updated July 14, 2026 and observed November 5, 2026. This several-month-old third-party estimate is not this site's traffic or a forecast.
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