How to Test Regular Expressions Online
Regular expressions are powerful but notoriously tricky to get right. A single misplaced quantifier can change your match entirely. Our regex tester gives you instant visual feedback so you can build, test, and refine patterns with confidence.
Try Regex Tester Now
Free, no signup. Works in your browser.
Enter your regex pattern
Type your regular expression in the pattern field at the top. Do not include the surrounding slashes — just the pattern itself. The tool parses it in real time and warns you about syntax errors.
Set flags
Toggle common flags like global (g), case-insensitive (i), multiline (m), dotAll (s), and unicode (u). Each flag modifies how the engine processes your pattern.
Provide test strings
Paste one or more test strings in the input area. Matches are highlighted instantly with color-coded groups so you can see exactly what each capture group is grabbing.
Inspect match details
Click on any highlighted match to see its index, length, and captured groups in the detail panel. This is invaluable for debugging complex patterns with multiple groups and backreferences.
Use the cheat sheet
Expand the built-in cheat sheet to look up character classes, quantifiers, anchors, and lookaheads without leaving the page. Each item includes a quick example you can click to insert.
Export and share
Copy the final regex or generate a permalink to share your pattern and test data with teammates. The URL encodes the pattern, flags, and test strings.
Pro Tips
- *Start with a simple pattern and add complexity — it is much easier to debug incrementally.
- *Use named capture groups `(?<name>...)` to make your regex self-documenting.
- *Always test edge cases: empty strings, special characters, and very long inputs.
- *Beware of catastrophic backtracking — avoid nested quantifiers like `(a+)+` on untrusted input.
- *Use non-capturing groups `(?:...)` when you need grouping but do not need the match result.
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