Online Regex Tester & Checker

A regex tester (regular expression tester) is a tool that lets you write a pattern and immediately see which parts of a text string match. Instead of running code in a terminal or browser console, you get live feedback as you type — matches are highlighted in real time, capture groups are displayed, and errors in your pattern are reported instantly.

This free online regex tester uses JavaScript's ECMAScript engine — the same engine that runs in every browser and in Node.js. Everything runs locally in your browser; no text or patterns are ever sent to a server.

1. 1.Enter your regular expression in the Pattern field. You can also pick a pre-built pattern from the Patterns dropdown (email, URL, UUID, and more).
2. 2.Toggle flags as needed — g for global, i for case-insensitive, m for multiline.
3. 3.Paste your test string in the left panel. Matches highlight live in the right panel, each capture group in its own colour.
4. 4.Check Match Details below for the position, line number, full match, and individual capture group values.
5. 5.Switch to the Replace tab to preview substitutions. Use $1, $2 or $<name> for named groups.

Here are the most frequently used regular expression patterns and what they match:

• ▸[a-zA-Z0-9._%+\-]+@[a-zA-Z0-9.\-]+\.[a-zA-Z]{2,} — matches a valid email address.
• ▸https?:\/\/[^\s]+ — matches a URL starting with http or https.
• ▸\d{4}-\d{2}-\d{2} — matches a date in YYYY-MM-DD format.
• ▸#(?:[0-9a-fA-F]{3}){1,2} — matches a hex color code like #fff or #f43f5e.
• ▸\b\w+\b — matches every individual word in a string.

Use the Patterns dropdown in the tester above to load any of these instantly.

This tool uses the JavaScript (ECMAScript) regex engine — the same one used in browsers, Node.js, and TypeScript. If you are writing regex for Python, PHP, Ruby, or Nginx, be aware of these differences:

• ▸PCRE (PHP, Python re, C, Nginx) supports possessive quantifiers (a++), atomic groups ((?>...)), and \K — none of which exist in JavaScript.
• ▸JavaScript supports named capture groups ((?<name>...)), lookahead, lookbehind, and the u (Unicode) and s (dotAll) flags.

For JavaScript, TypeScript, or Node.js regex — this is the right tester. For other languages, the patterns are largely compatible but test in the target environment before deploying.