---
title: Regex Tester — Live Match Highlighting & Capture Groups
url: https://varstatt.com/toolkit/regex
description: Test regular expressions with live highlighting, capture groups, pattern explanation, and quick-reference. Export in JS, Python, or Go.
section: Developer Toolkit (https://varstatt.com/toolkit)
tags: text
related: Case (https://varstatt.com/toolkit/case), Slug (https://varstatt.com/toolkit/slug), Regex (https://varstatt.com/toolkit/regex)
---
# Regex Tester

Test regular expressions with live highlighting, capture groups, pattern explanation, and quick-reference. Export in JS, Python, or Go.

## How It Works

1. **Write your pattern** — Enter a regular expression and toggle flags (global, case-insensitive, multiline, etc.).
2. **Test against sample text** — Paste your test string and see all matches highlighted in real-time.
3. **Inspect and export** — View capture groups, read the pattern explanation, and copy in JS, Python, or Go format.

## FAQ

### Which regex engine is used?

The tool uses your browser's native JavaScript RegExp engine, which supports ES2018+ features including named groups and lookbehind.

### Why is my regex slow?

Catastrophic backtracking can occur with nested quantifiers like (a+)+. The tool shows execution time to help identify slow patterns.

### Can I test multiline strings?

Yes. Enable the 'm' flag to make ^ and $ match line boundaries, and the 's' flag to make . match newlines.

## Usage

This tool runs entirely in the browser — visit the URL above to use it.

Prefill inputs via URL parameters:

- `https://varstatt.com/toolkit/regex?pattern=...&flags=...&input=...`

## Related Tools

- [Case](https://varstatt.com/toolkit/case)
- [Slug](https://varstatt.com/toolkit/slug)
- [Regex](https://varstatt.com/toolkit/regex)