Regex Tester - Test Regular Expressions Online
Test and debug regular expressions online with live highlighting. Supports JavaScript regex with flags, capture groups, and match details.
About this calculator
Type a regular expression and some test text and see every match highlighted as you type. Choose flags such as g (all matches), i (ignore case) and m (multi-line).
It uses JavaScript regex syntax, so it matches what you get in the browser and in Node.js.
How to use it
- Enter the pattern and flags.
- Type or paste the test text.
- Press Test Regex and read the matches.
Regex building blocks
. any character; \d digit; \w letter, digit or underscore; \s whitespace; \b word boundary; * zero or more; + one or more; ? optional; {n,m} between n and m; ^ and $ start and end; (…) group; a|b either. Flags: g global, i ignore case, m multi-line, s dot matches newline.
Worked example
Pattern \b\w+ing\b with flags gi
| Text | The running fox is jumping over the lazy dog |
| Matches | running, jumping |
Tips and common mistakes
- Start simple and add pieces one at a time.
- Use \b to avoid matching inside longer words.
- Greedy quantifiers match as much as possible; add ? to make them lazy.
- Escape special characters like . and ? with a backslash.
- Test with both matching and non-matching examples.
Frequently asked questions
What is a regular expression?
A pattern used to match text.
What does the g flag do?
Finds all matches, not just the first.
What is the difference between * and +?
* allows zero repeats, + needs at least one.
How do I match a literal dot?
Escape it: \.
What is a capture group?
Parentheses that capture part of a match for reuse.
Why does my regex match too much?
Quantifiers are greedy; make them lazy with ?.