What is a regex tester?
A regex tester runs a regular expression against sample text and shows each match, its position, and any capture groups.
Regex Tester & Debugger
Test JavaScript regular expressions, inspect capture groups, and explain patterns locally in your browser.
How it worksTest Target String
Matched Results
Match Information
Regex Explanation
How to test a regular expression
- Enter a JavaScript regular expression pattern.
- Enable the flags that match your use case.
- Paste text into the test-string editor.
- Review highlighted matches, character positions, capture groups, and the pattern explanation.
Common regex testing uses
Validate email-like strings, find IDs or log entries, extract values from text, test form validation rules, and debug search patterns before adding them to code.
Regex testing tips
- Escape literal special characters such as . and + with a backslash.
- Use the global flag to inspect every occurrence in the test text.
- Test edge cases such as empty values, line breaks, and unexpected punctuation.
Regex Tester FAQ
Which regular expression flavor does this tool use?
It uses the JavaScript regular expression engine available in modern browsers.
What does the global g flag do?
The g flag finds every match. Without it, a JavaScript RegExp typically stops after the first match.
What does the i flag do in regex?
The i flag makes letter matching case-insensitive, so a pattern can match uppercase and lowercase text.
What do the m and s flags do?
The m flag lets ^ and $ match line boundaries; the s flag lets a dot match line breaks.
Can I inspect capture groups?
Yes. Each match lists its full text, character range, and numbered capture groups.
Why is my regex invalid?
Check for unclosed parentheses or brackets, invalid quantifiers, or unsupported syntax for JavaScript regular expressions.
Is my test text private?
Yes. Matching runs locally in your browser and DevKit does not upload or store your pattern or test text.
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