Regex Tester & Debugger
Test regular expressions live against sample text with match highlighting, capture groups, and a cheat sheet.
How to Use Regex Tester & Debugger
Type your regular expression and set flags (global, case-insensitive, multiline, dotall, unicode).
Paste your sample text or log lines into the test area.
Watch matches highlight live; expand the matches panel to inspect capture groups and positions.
Copy your finished pattern โ or sample replacement output using the replace field.
About Regex Tester & Debugger
Build and debug regular expressions safely with instant visual feedback. Enter a pattern and flags, paste your sample text, and watch every match highlight in real time as you type โ including numbered and named capture groups, match positions, and a per-match breakdown panel. A built-in quick reference covers the syntax that actually works in JavaScript (lookaheads, quantifiers, character classes, unicode flags), and every evaluation runs locally with hard timeout protection, so a catastrophic-backtracking pattern freezes your test instead of your whole page.
Frequently Asked Questions
Which regex flavor does this use?
JavaScript (ECMAScript) regex โ the same engine used by Node.js and browser JavaScript, and very close to PCRE for everyday patterns. Lookbehind and unicode property escapes are supported on all modern browsers.
Is my data or my regex sent anywhere?
No. Pattern matching runs locally with the native RegExp engine. Your logs, payloads, and patterns never leave the page.
What happens if my pattern is catastrophically slow?
A watchdog limits each match run, so pathological patterns (nested quantifier backtracking) are flagged with a warning instead of hanging your browser indefinitely.
Can I test substitutions, not just matches?
Yes. Enter a replacement string to preview the full substituted output alongside the highlighted matches.
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