Test Regex Patterns
Without Uploading Them
Live match highlighting, capture groups, flag toggles. Paste real production data — nothing leaves your browser.
Why Private Regex Testing Matters
Most online regex testers are fine for learning syntax. The problem shows up the moment you paste real data — production logs with customer emails, API keys from a config file, JWT tokens, database rows. That content gets transmitted to the testing site's server, appears in their access logs, and may sit there indefinitely.
A browser-native regex tester uses the same JavaScript RegExp engine that runs in Node.js and every modern browser, so patterns you verify here behave identically in your application code. Nothing is transmitted, nothing is logged, and you can prove it in DevTools.
Regex Flag Reference
| Flag | Name | Effect | Common Use |
|---|---|---|---|
| g | Global | Find all matches, not just the first | Extract every email from a document |
| i | Ignore case | A matches a, Z matches z | Search log files for ERROR / error |
| m | Multiline | ^ and $ match start/end of each line | Validate one-per-line input |
| s | Dotall | . matches newlines too | Match across multi-line blocks |
| u | Unicode | Full unicode + \p{...} classes |
Match emoji, non-Latin scripts |
| y | Sticky | Match from lastIndex only |
Hand-rolled tokenizers |
Regex Tester Comparison
| Tool | Test Data Uploaded? | Flavors | Safe for Production? |
|---|---|---|---|
| ResourceCentral | Browser only | ECMAScript / JS | ✓ Yes |
| regex101.com | Mostly client-side, optional save | PCRE, JS, Python, Go | Check save-pattern setting |
| regexr.com | Client-side with cloud community | JS, PCRE | Disable sharing |
| Browser DevTools | Local only | ECMAScript / JS | ✓ Yes |
Fair credit: regex101 and regexr are excellent for multi-flavor work and learning. This tool exists for the narrower case where patterns and test data must stay fully local.
FAQ
Is it safe to test regex on production data here? +
Yes. Matching runs entirely in your browser using the native JavaScript RegExp engine. Patterns and test strings never leave your device — no server upload, no logging. Safe for production logs, config files, and data with real identifiers.
Which regex flavor does this tester use? +
ECMAScript / JavaScript regex — the flavor used in Node.js, browsers, TypeScript, and most modern web frameworks. Patterns verified here behave identically to String.prototype.matchAll and RegExp.prototype.exec in your application code.
Does this support named capture groups and lookbehinds? +
Yes. Named groups like (?<year>\d{4}) appear in the match panel with their captured values labeled. Lookaheads (?=...), lookbehinds (?<=...), and backreferences \1 all work in modern browsers.
Why does my regex work here but fail in Python or Go? +
Regex flavors differ between languages. Python's re module has slightly different escape rules and named-group syntax. Go's RE2 deliberately omits lookaheads and backreferences for predictable performance. Always test in the target language before deploying — this tool covers the JavaScript side cleanly.
What happens with catastrophic backtracking? +
A pattern like (a+)+$ against long input can hang your browser tab. Matching is wrapped in a timing measurement (performance.now()) so you'll see if a pattern takes unreasonably long — that's a signal to rewrite it using atomic groups or possessive quantifiers before deploying.
Test Your Regex Now
Paste at the top of this page. No account. No uploads. Works on any device.
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