JavaScript Regex Tester Online

Check regex JavaScript patterns against sample text, debug flags, inspect match indexes and review capture groups before using them in browser, Node.js or TypeScript code.

Tool

Results will appear here.

Quick example

/hello/gi

Test text:

Hello hello

Result:

2 matches found at indexes 0 and 6

Common JavaScript regex examples

Use these examples as safe starting points, then adjust them for your real input. A regex tester is most useful when you paste realistic sample text instead of only testing the perfect case.

How to use

1. Enter a raw pattern such as \d+, or paste a JavaScript regex literal such as /hello/gi.
2. Select the flags you need. Global is enabled by default so every match is returned.
3. Paste or type the text to test.
4. Click “Test Regex” or press Ctrl/Command + Enter to see each match, its index and any capture groups.

The result displays at most the first 1,000 matches. Testing runs away from the page interface and stops after 1.5 seconds, so an accidental expensive pattern cannot leave the tab permanently frozen.

Supported JavaScript regex flags

• g — global search, returns every match instead of only the first one.
• i — ignore case, so hello can match Hello.
• m — multiline anchors, so ^ and $ work per line.
• s — dotAll mode, so . can match newline characters.
• u — Unicode mode, useful for modern text and safer character handling.

You can select flags with the checkboxes or paste a JavaScript literal such as /error|warning/gi. This helps you check regex JavaScript behavior before copying the pattern into code.

Troubleshooting regex errors

• If you see an “unterminated group” error, check that every ( has a matching ).
• If a pattern returns too many matches, try a more specific character class instead of a broad .*.
• If line-based matching does not work, enable the m flag and test with realistic multi-line text.
• If a capture group is empty, simplify the pattern and test each part step by step.

Common use cases

Regex Tester is useful for checking JavaScript validation patterns, matching IDs in logs, extracting text fragments and debugging capture groups before shipping code. The result includes each match and its zero-based index so you can verify where the expression matched.

Use it for quick browser, Node.js and TypeScript regex checks when you need to confirm exact JavaScript behavior. Paste a raw pattern or a literal like /[A-Z]+/gi, add sample text and verify the output before changing production code.

What is a Regex Tester?

A regex tester lets you run a regular expression against sample text before adding it to your code. This tester uses the browser's native JavaScript RegExp engine, so its syntax and behavior match modern browser, Node.js and TypeScript projects.

Flags change how the same pattern behaves. Use g to return every match, i to ignore letter case, m to make line anchors work per line, s to let a dot match newline characters and u for Unicode-aware parsing.

For example, /hello/gi finds both “Hello” and “hello”. If a pattern is invalid, the tool shows the JavaScript error so you can correct it. All testing happens locally in your browser.

Regex tester questions

What is a regex tester?
It runs a regular expression against sample text and reports the matches, positions and capture groups so you can debug a pattern before using it in code.

Is this regex tester compatible with JavaScript?
Yes. It is designed around JavaScript RegExp behavior, which makes it useful for browser code, Node.js and TypeScript projects.

What regex flags are supported?
The tool supports global (g), case-insensitive (i), multiline (m), dotAll (s) and Unicode (u). You can combine them or paste them in JavaScript literal syntax.

Learn with a practical guide

If you are not sure how to test a JavaScript pattern safely, read the step-by-step guide: How to test JavaScript regex patterns.

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