Regex Tester

Test and debug regular expressions with live match highlighting, capture groups, flags and a quick reference. Free tool for developers.

The Regex Tester lets you write a JavaScript regular expression, apply it to a sample text, and see matches highlighted live as you type, along with any capture groups the pattern defines. It is aimed at developers writing validation rules, search-and-replace patterns or parsing logic who want fast, visual feedback rather than testing inside their actual application code.

Because it uses the browser's native regex engine, results match exactly what your JavaScript code will do at runtime, including support for named capture groups, lookahead and lookbehind assertions in modern browsers. Toggle flags like global, case-insensitive and multiline to see how they change which parts of the text are matched.

How to use the Regex Tester

1. Type or paste your regular expression pattern into the pattern field.
2. Toggle flags such as g (global), i (case-insensitive) or m (multiline) as needed.
3. Paste your sample text into the test string area.
4. Review the highlighted matches shown live in the text.
5. Check the capture groups panel to see what each group captured for every match.
6. Adjust the pattern and repeat until the matches are exactly what you need.

Why use this tool

Live match highlighting

Matches are highlighted directly in the sample text as you edit the pattern, making it immediately obvious whether the regex is too broad, too narrow, or matching the wrong part of the string.

Capture group breakdown

Named and numbered capture groups are listed separately for each match, which is essential when a pattern is being used to extract specific pieces of data rather than just test for a match.

Matches real JavaScript behaviour

Because the tool runs the browser's actual regex engine, the results reflect exactly how the same pattern will behave in your JavaScript code, avoiding surprises from a different regex flavour.

Common use cases

• Building and testing a validation pattern for email addresses or phone numbers.
• Debugging why a regex used in a form validator is rejecting valid input.
• Designing a search-and-replace pattern before running it across a codebase.
• Extracting structured data like dates or IDs from log files using capture groups.
• Learning how flags such as global and multiline change matching behaviour.

Regex flavour used

This tool uses JavaScript's built-in (ECMAScript) regular expression engine, the same one used by Node.js and every modern browser. This includes support for named capture groups such as (?<year>\d{4}), and lookahead and lookbehind assertions in current browser versions.

Understanding flags

The g flag finds all matches instead of stopping at the first one, i makes matching case-insensitive, m changes ^ and $ to match the start and end of each line rather than the whole string, and s allows . to match newline characters. Combining flags like gi is common for global, case-insensitive searches.

Common regex mistakes

Forgetting to escape special characters like . or ( when they should be literal is a frequent source of unexpected matches. Overly greedy quantifiers such as .* can also match far more text than intended; switching to a non-greedy .*? or a more specific character class usually narrows the match correctly.

Frequently asked questions

Which regex flavour does this use?

JavaScript (ECMAScript) regular expressions, including named capture groups, lookahead and lookbehind in modern browsers.

What do the g, i and m flags do?

g finds every match rather than just the first, i makes matching case-insensitive, and m makes ^ and $ match at each line break instead of only the whole string.

Is Regex Tester free to use?

Yes. Regex Tester on Klipza is completely free with no account, no subscription and no watermark on your files, and there is no daily usage limit.

Are my files safe when using Regex Tester?

Processing happens locally in your browser wherever technically possible, so your files are not uploaded to a server, stored or shared with third parties.

Does Regex Tester work on mobile phones?

Yes. It is fully responsive and runs in any modern browser on Android, iPhone, iPad, Windows and macOS — nothing to install.