Regex Tester
Live matching, highlight, capture groups, and replace — client-side.
Pattern
Flags
Mode
Replacement
matches
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About regex testing
Regular expressions are the standard tool for validating input, extracting substrings, and rewriting text — and the fastest way to get them right is to iterate live against real samples. This tester runs JavaScript's native RegExpengine in your browser: type a pattern, watch matches highlight as you type, inspect capture groups, and flip to replace mode to see a rewrite applied.
Flags
g matches every occurrence (highlight mode forces it so all matches appear), i ignores case,m makes ^and $ match line starts and ends,s lets .match newlines, u switches to Unicode semantics, and y makes matching sticky to the previous position.
Zero-width matches
A pattern like a* can match an empty string, which on many sites makes a regex tester hang or flood the page with zero-width results. This tool advances past zero-width matches automatically and skips them in the highlight, so you can experiment freely with quantifiers like* and ?.
Related tools
Validate the result against structured data with the JSON formatter, or build a reusable config in the JSON to YAMLconverter.
FAQ
Can regex testing hang my browser?
No. Patterns that can match empty strings (like /a*/g) are handled with a guard that advances past zero-width matches, and the tool caps runaway matching.
Is my pattern or text sent anywhere?
No. Matching uses native JavaScript RegExp entirely in your browser — nothing is uploaded.