Regex Tester

Test and debug regular expressions in real time. See matches, groups and flags explained.

Regular Expression

/ /

g Global i Insensitive m Multiline s DotAll u Unicode

Test String

Match Details

No matches yet

Quick Reference

. Any char

\d Digit

\w Word char

\s Whitespace

^ Start

$ End

* 0 or more

+ 1 or more

? 0 or 1

{n} Exactly n

[abc] Char class

(...) Group

| Or

About the Regex Tester

The Regex Tester lets you write, test and debug JavaScript regular expressions in real time directly in your browser. Matches are highlighted inline as you type, and every capture group is listed with its index and value - making it easy to spot exactly what your pattern captures. No server requests, no signup - everything runs client-side for instant feedback.

Common use cases

Validating email addresses, phone numbers, or postal codes with a pattern before using it in code
Extracting specific fields (dates, URLs, IDs) from raw log files or API responses
Testing search-and-replace patterns before running them in an editor like VS Code
Learning regular expression syntax with the built-in quick reference cheat sheet

Frequently Asked Questions

How does the Regex Tester work technically?

The Regex Tester runs entirely in your browser using JavaScript's native RegExp engine - the same engine used by V8 (Chrome, Edge, Node.js) and SpiderMonkey (Firefox). Your pattern and test string are never sent to a server; all matching, capture-group extraction, and highlighting happen locally in real time as you type. Because it uses the JS engine directly, the results mirror exactly what you would see in your own JavaScript code.

Is my regex pattern or test text stored anywhere?

No data is stored on any server. Both the regular expression pattern and the test string exist only in your browser's memory while the page is open and are discarded the moment you close or refresh the tab. There are no accounts, no logs, and no analytics that capture the content of your inputs - your patterns and strings stay completely private.

What are the limitations compared to server-side regex engines?

Because the tester uses the JavaScript RegExp engine, it does not support PCRE-only features such as lookbehind assertions longer than a fixed length (in older browsers), atomic groups, possessive quantifiers, or named subroutines found in PHP, Python, or .NET regex flavours. If you need to test a pattern for a different language, be aware of these differences - for example, Python's re module uses a distinct syntax for named groups. The tool is best suited for patterns that will be used in JavaScript, Node.js, or TypeScript projects.

Which browsers are supported?

The Regex Tester works in all modern browsers including Chrome 90+, Firefox 88+, Safari 14+, and Edge 90+. Internet Explorer is not supported because it lacks the ES6 features used for real-time rendering. For the best experience - including support for newer regex features such as named capture groups ((?<name>...)) and the d (indices) flag - use an up-to-date Chromium-based browser or Firefox.

How does this compare to tools like regex101 or regexr?

Unlike regex101, which supports multiple engine flavours (PCRE, Python, Java, .NET) by sending your pattern to a backend server, this tester is fully client-side and focused on JavaScript. It's faster to load, requires no sign-in, and has no usage limits. Tools like regexr offer a larger community library of saved patterns, whereas this tool prioritises a minimal, distraction-free UI with inline match highlighting and an integrated capture-group inspector - ideal for quick testing during active development.

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