Free Online Regex Tester
Test JavaScript regular expressions live. See every match and capture group highlighted, preview replacements and read a plain English explanation of the pattern.
Online Regex Tester: Test JavaScript regular expressions live. See every match and capture group highlighted, preview replacements and read a plain English explanation of the pattern. It is free, needs no sign-up and runs in your browser. How to use it: 1) type a pattern or pick one from the common patterns; 2) set flags and paste your test text; 3) read the highlighted matches, groups table and explanation, then copy the code. The tester uses your browser’s own JavaScript regular expression engine, so results match what your code will do in Chrome, Node.js and other modern runtimes. As you type, it finds every match, highlights matches in alternating colours and underlines capture groups.
How the regex tester works
The tester uses your browser’s own JavaScript regular expression engine, so results match what your code will do in Chrome, Node.js and other modern runtimes. As you type, it finds every match, highlights matches in alternating colours and underlines capture groups. A table lists each match with its position and the value of every numbered and named group.
Flags
gfinds all matches instead of only the first.iignores upper and lower case.mmakes ^ and $ work on each line.slets the dot match line breaks.uenables Unicode features such as\p{L}.ymatches only at the current position.
Replace preview and explanation
Type a replacement to see the result instantly. Use $& for the whole match, $1 for a group and $<name> for a named group. The explanation breaks the pattern into tokens such as character classes, quantifiers, anchors, groups and lookarounds, and describes each in plain English.
Common patterns
The library includes email, URL, US and international phone numbers, Pakistan mobile numbers, US ZIP codes, UK and Canadian postcodes, IPv4, dates, times, hex colours, strong passwords, slugs, HTML tags, hashtags and duplicate words. Treat them as practical starting points rather than complete validators.
Limitations
Patterns run in a background worker and stop after 2 seconds, which protects the page from catastrophic backtracking. Other languages such as PCRE, Python or Java support some syntax that JavaScript does not.
Regex Tester FAQs
Which regex flavour does this tester use?
It uses JavaScript (ECMAScript) regular expressions, the same engine your browser and Node.js run. Most syntax is shared with PHP, Python and Java, but some features differ, such as possessive quantifiers or inline modifiers. Test patterns in the language you deploy when you rely on advanced features.
How do I match an email address with regex?
Click Email in the common patterns. It matches text, an @ sign, a domain and a top level domain of at least two letters, which catches nearly all real addresses. Perfect email validation by regex is impossible, so confirm important addresses by sending a verification message.
What are capture groups and named groups?
Parentheses capture the part of the match inside them so you can reuse it, for example in a replacement with $1. Named groups such as (?
Why does my regex freeze or take too long?
Patterns with nested quantifiers like (a+)+ or overlapping alternatives can try millions of combinations on text that almost matches. This is called catastrophic backtracking. The tester stops after 2 seconds and warns you. Make the pattern more specific or remove nested repetition to fix it.
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