Regex Tester
Test regex patterns with match highlighting and group capture
//g
Overview
Enter a regex pattern and see matches highlighted in your test string in real time. Capture groups are displayed separately as well. Being able to test and iterate on patterns instantly saves a lot of debugging time.
Key Features
- Real-time match highlighting
- Capture groups displayed separately
- Flag selection (g, i, m, s, u)
- Match count and position information
- Common regex pattern examples included
How to Use
- Write the regex pattern in the top input field.
- Select the flags you need (g, i, m, etc.).
- Enter the test string in the text area below.
- Matches are highlighted and capture groups are shown separately.
Tips
- Enable the g (global) flag to find all matches. Without it only the first match is shown.
- There is no perfect email regex. Do a simple format check with regex and verify with a confirmation email.
- (?:...) is a non-capturing group -- it groups without adding to the capture results.
FAQ
- Which regex engine does this use?
- It uses JavaScript's RegExp engine. Most patterns are compatible with Python and Java regex, but some advanced features like lookbehind may vary by browser.
- What are capture groups?
- Capture groups are the parts of a pattern enclosed in parentheses (). They let you extract specific portions of the matched text, which is useful for pulling out particular values.
- Can a complex regex cause performance issues?
- Yes, patterns with nested quantifiers can cause catastrophic backtracking. With long test strings, this can freeze the browser. Be careful with patterns like (a+)+ or (a|a)+.