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Free Online Regex Tester

//g
Test String
Highlighted Matches

Matches will be highlighted here...

What is a Regular Expression?

A Regular Expression (regex) is a sequence of characters that defines a search pattern. Regex is used in virtually every programming language for string matching, validation, search-and-replace operations, and data extraction. Common use cases include email validation, URL parsing, log file analysis, and text transformations.

Our regex tester lets you write patterns and instantly see matches highlighted in your test text. It shows capture groups, match indices, and supports all JavaScript regex flags. Perfect for building and debugging complex patterns before using them in your code.

Key Features

Real-Time Matching

Matches update instantly as you type - no button clicks needed.

Capture Groups

View captured groups ($1, $2, ...) for each match with clear labeling.

All JS Flags

Toggle g (global), i (case-insensitive), m (multiline), s (dotall) flags.

Visual Highlighting

Matched text is highlighted in yellow for instant visual feedback.

Frequently Asked Questions

Which regex flavor does this tool support?
This tool uses JavaScript's native RegExp engine, which supports ECMAScript regex syntax including lookaheads, lookbehinds (ES2018+), named capture groups, and Unicode escapes.
What do the flags mean?
g = find all matches (not just the first), i = case-insensitive matching, m = ^ and $ match start/end of each line, s = dot (.) matches newline characters.
How do I use capture groups?
Wrap parts of your pattern in parentheses: (\w+)@(\w+) captures the username and domain separately. Groups are shown as $1, $2, etc. in the match details.
Is my data private?
Yes. All regex processing happens in your browser using JavaScript's native RegExp. No data is sent to any server.

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About the Regex Tester

Regular expressions are powerful but easy to get wrong. The Regex Tester lets you build and debug patterns against your own sample text with real-time match highlighting, so you can see exactly what your expression captures before you drop it into code. It supports flags like global, case-insensitive, and multiline matching.

How to use the Regex Tester

  1. 1Enter your regular expression pattern.
  2. 2Toggle flags such as g (global), i (case-insensitive), and m (multiline).
  3. 3Paste sample text to test against.
  4. 4Matches are highlighted live, and capture groups are listed so you can refine the pattern.

Frequently asked questions

Which regex flavor does this use?

It uses the JavaScript (ECMAScript) regular expression engine, the same one that runs in browsers and Node.js.

What do the flags mean?

g matches all occurrences instead of just the first, i ignores case, m makes ^ and $ match at line breaks, and s lets the dot match newlines.

Why is my pattern not matching?

Common issues are unescaped special characters (like . or ?), missing flags (for example needing g for multiple matches), or greedy quantifiers capturing more than expected. Test incrementally with small patterns.

Is my test data private?

Yes. Everything runs in your browser and no text is uploaded.

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