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Regex Pattern Tester
Regex Pattern Tester runs a regular expression against your text and lists every match with its position and captured groups, which is the fastest way to check a pattern before putting it into code.
How to use Regex Pattern Tester
- Type the pattern and its flags in the two fields.
- Paste the text to search into the editor.
- Run the test to see each match, its start position and any capture groups.
Where Regex Pattern Tester is useful
- Checking an email or URL validation pattern before shipping it.
- Seeing exactly what a capture group will return.
- Debugging why a pattern matches too much or too little.
- Learning how flags such as i and g change matches.
Formats, algorithms and limits
Patterns use JavaScript regular expression syntax, so what you test here behaves identically in Node and in the browser. The global flag is added automatically when you omit it, because a pattern without g can only report the first match while a test tool should list them all. Positions are character indices into the text as pasted.
Troubleshooting and honest limits
- Test against text that should NOT match as well as text that should — false positives are the usual bug.
- Remember that . does not match line breaks unless you enable the s flag.
- Escape a literal dot as \. when validating domains or file extensions.
Frequently asked questions
Which flavour of regular expressions is used?
JavaScript, so lookbehind and named groups are supported in any modern browser. Patterns behave the same in your code if you use JavaScript.
Why does my pattern only return one match?
That happens without the global g flag. This tester adds g for you when it is missing so that all matches are listed.
What do the capture groups show?
Each group is the text captured by one set of parentheses, in order. Groups appear in the results alongside the full match.
Can I use the result to replace text?
The tester shows matches; use the pattern with your language's replace function, or the Text Diff tool to check the result of the substitution.
Related tools
Page written and reviewed by the FreeConvertio engineering team on 2026-10-14. Regex Pattern Tester runs entirely in your browser — no uploads, no account and no daily limits.