Regex Tester — Test & Debug Regular Expressions Online Free
Free online regex tester to test and debug regular expressions with live matching. Visualize pattern matches, test replacements, and explore regex syntax with detailed explanations. Supports flags, groups, lookaheads, and backreferences.
Example Patterns
How to Use the Regex Tester
Enter your regex pattern
Type or paste a regular expression pattern into the Pattern field.
Choose flags
Toggle flags like Global, Case Insensitive, and Multiline to control matching behavior.
Enter test text
Paste the text you want to test against in the Test String area.
Review matches and groups
View highlighted matches, capture groups, and use the Replace tab to test substitutions.
Frequently Asked Questions
It uses JavaScript's built-in RegExp engine, supporting standard ECMAScript regex syntax.
Yes. Switch to the Replace tab, enter a replacement pattern, and see the result instantly.
Flags modify how the pattern matches: g (global), i (case insensitive), m (multiline), s (dotAll), u (unicode), y (sticky).
Use $1, $2, etc. for numbered groups, $& for the full match, and $` or $' for text before or after the match.
Example Results
Try this sample text
The quick brown fox jumps over the lazy dog.
What you'll see
Pattern /the/gi → 2 matches at positions 31 and 40
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