About the Regex Tester
Regular expressions (regex) are powerful patterns for searching, matching, and replacing text. They can also be hard to get right. This free online Regex Tester lets you build and debug patterns interactively, with every match highlighted in your test string as you type.
It uses your browser's native JavaScript regex engine, so behavior matches what you'll get in real JavaScript code. Toggle flags like global, case-insensitive, and multiline, and instantly see how many matches your pattern finds.
How to test a regex
- Type your regular expression into the pattern field (no slashes needed).
- Toggle the flags you need, such as g (global) or i (case-insensitive).
- Paste or type the text you want to test against.
- Matches are highlighted instantly and the match count is shown.
- Refine the pattern until it matches exactly what you intend.
Features
- Live match highlighting as you type.
- All JavaScript regex flags: g, i, m, s, u, y.
- Match count and clear error messages for invalid patterns.
- Uses the native JavaScript regex engine for accurate results.
- 100% client-side — your patterns and text stay in your browser.
Regex Tester & Debugger FAQs
What regex syntax does this tester support?
It uses the JavaScript (ECMAScript) regular expression engine, so any pattern valid in JavaScript works here, including character classes, groups, lookaheads, and named groups.
What do the flags mean?
g matches globally, i is case-insensitive, m is multiline, s lets the dot match newlines, u enables Unicode mode, and y is sticky matching.
Why does my pattern show an error?
The error means the pattern is not valid regex syntax — for example, an unclosed group or bracket. The message from the engine tells you what went wrong.
Is my test data private?
Yes. All matching happens locally in your browser. Your pattern and text are never uploaded or stored.
Is the regex tester free?
Yes, it is completely free, requires no signup, and works entirely in your browser.
