# Regex tester & playground — in your browser, no upload

> Test and debug regular expressions against sample text with live match highlighting, in your browser. No upload — everything runs on your device.

Write a regular expression and see what it matches in your sample text as you type, with highlighting and capture groups. It all runs locally in your browser.

A regex tester is where you build a pattern safely before dropping it into code that runs against real data. Live highlighting turns the usual guesswork — why does this match too much? why does it skip that line? — into something you can see immediately.

Toggle flags to understand their effect, watch capture groups populate, and iterate until the pattern does exactly what you intend. Because it is JavaScript regex, it mirrors what you will get in the browser or Node.

For extracting many matches out of a big document, use the Data Zone regex extraction tool; for a quick syntax refresher, see the regex cheatsheet.

## How to

1. **Enter a pattern.** Type your regular expression and set flags like global, case-insensitive, or multiline.
2. **Paste test text.** Add the sample text you want to match against.
3. **See live matches.** Matches highlight as you type, with capture groups broken out.
4. **Use it.** Copy the working pattern into your code once it behaves.

## FAQ

### Which regex flavor is this?

JavaScript (ECMAScript) regular expressions, matching what runs in browsers and Node — mind the small differences from PCRE or Python.

### What do the flags do?

'g' finds all matches, 'i' ignores case, 'm' makes ^ and $ match line boundaries, and 's' lets '.' match newlines.

### Can I see capture groups?

Yes. Each match shows its numbered (and named) capture groups so you can confirm what you are extracting.

### Is my test text uploaded?

No. Matching runs in your browser tab; your patterns and sample data stay on your device.


## Related tools

- [Regex extractor](https://www.safepaper.app/data/regex-extract)
- [JSON toolkit](https://www.safepaper.app/dev/json-toolkit)
- [Base64](https://www.safepaper.app/dev/base64)
- [Format swap](https://www.safepaper.app/data/csv-to-json)

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Canonical HTML: https://www.safepaper.app/dev/regex-playground
Markdown: https://www.safepaper.app/dev/regex-playground.md

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