Developer
Regex Tester
Test JavaScript regular expressions with flags, matches, and optional replacements.
Use tool ↓Regex Tester
Test JavaScript regular expressions with live match highlighting, flags, and replacement. Free regex tester — runs in your browser instantly, no login needed. This tool is designed for fast, browser-first execution so you can finish routine tasks without switching apps. Everything runs locally in your browser — your data stays on your device unless the tool explicitly calls an API.
How to Use
- Open the Regex Tester tool on it3.site
- Enter or paste your input in the fields above
- Click the primary action button to process your data
- Copy or download the result for your project
- Bookmark this page for quick access later
Key Features
- Free Regex Tester u2014 no signup required
- Runs entirely in your browser for privacy
- Mobile-friendly responsive interface
- Part of it3u2019s Developer tool suite
- Fast results with no file uploads to our servers (unless noted)
- Works offline after the page loads
Frequently Asked Questions
Flavors matter?
This uses JavaScript `RegExp`u2014PCRE lookahead or backreference rules differ from grep or Ruby; confirm engine when porting patterns.
Catastrophic backtracking?
Nested quantifiers like `(a+)+$` can freeze the tab; keep alternation tight and test with short strings first.
Unicode property escapes?
Require `u` flag and ES2018+ supportu2014Safari versions vary; verify target matrix.
Replacement callbacks?
We only show simple string replacementu2014`$1` groups work but function replacers are out of scope here.
Security?
Never run user-supplied regex on servers without sandboxingu2014ReDoS is real.
Performance on huge haystacks?
Megabyte logs belong in ripgrep, not interactive browsers.
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