Regex Tester Online - Free Regular Expression Testing Tool

Test regular expressions in real-time. Fast, secure, and completely free. All processing happens in your browser — no data is sent to any server.

What is a Regex Tester?

A Regex Tester lets you write a regular expression and immediately see which parts of a sample text it matches, highlighted inline, along with each capture group's value. Regular expressions are notoriously easy to get almost right and hard to get exactly right — a quantifier that's greedy when you meant lazy, a character class missing one edge case, an anchor that doesn't do what you assumed — and the fastest way to catch those mistakes is to test against real, varied sample input rather than mentally tracing the pattern.

How to Use Regex Tester

1. Type your regular expression pattern into the pattern field
2. Paste sample text you want to test it against — ideally including edge cases
3. Matches are highlighted directly in the text as you type
4. Expand the match details to see each capture group's extracted value
5. Toggle flags (global, case-insensitive, multiline) to see how they change the matching behavior

Key Features

• Live match highlighting as you edit the pattern or test text
• Displays capture groups and their individual matched values
• Supports standard regex flags: global, case-insensitive, multiline, dotall
• Shows match count and position (start/end index) for each match
• Works entirely in your browser using the native JavaScript regex engine

Why Use Regex Tester?

Writing a regex against production data — validating an email format, extracting a value from a log line, splitting a CSV field — almost always surfaces an edge case you didn't think of on the first attempt: an email with a plus sign, a log line with an unexpected extra space, a field containing an escaped delimiter. Testing against a batch of representative examples before shipping the pattern catches those cases in seconds instead of after a bug report.

Common Use Cases

• Validating that an email or phone number pattern handles real-world edge cases
• Extracting a specific value (an ID, a date, a version number) from log lines
• Debugging why a regex used in code isn't matching the input you expect
• Testing a find-and-replace pattern before running it across a large codebase
• Learning regex syntax by seeing immediate, visual feedback on each change

Frequently Asked Questions

Which regex flavor does this tool use — JavaScript, PCRE, or something else?

It uses the native JavaScript regex engine, so patterns and flags behave exactly as they would in a browser or Node.js. Some PCRE-specific features (like certain lookbehind variations in older engines) may behave slightly differently in other languages.

Why does my pattern only match once when I expect multiple matches?

Add the global (g) flag — without it, most regex methods stop after the first match, even if the pattern could technically match again later in the string.

What's the difference between greedy and lazy quantifiers?

A greedy quantifier (like .*) matches as much text as possible before backing off, while a lazy quantifier (.*?) matches as little as possible — this distinction is a very common source of unexpected matches spanning too much or too little text.

Can I test multiline text against my pattern?

Yes, paste multiline sample text and toggle the multiline (m) flag if you need ^ and $ to match the start/end of each line rather than only the start/end of the whole string.

Is my test text or pattern sent anywhere?

No, matching runs entirely in your browser's JavaScript engine, so any sensitive sample data you're testing against stays local.

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