Regex Tester

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Common Patterns

Test String

Enter a pattern and test string to see matches.

About Regex Tester

The Regex Tester lets you write, test, and debug regular expressions against sample text in real time. Match highlights, a live replacement preview, and a capture-group breakdown all update as you type, making it easy to inspect groups and refine patterns. Supports the full JavaScript regex syntax including lookaheads, named capture groups, and all standard flags.

How it Works

1Type your pattern and toggle the flags you need (g, i, m, s, u).
2Paste sample text — matches highlight immediately and a capture-group breakdown shows how often each numbered or named group fires.
3Switch to the Replace tab and type a replacement string; the preview re-renders on every keystroke (use $1, $2 for numbered groups).
4Open Export code to copy an equivalent snippet in JavaScript, Python, Java, or Go.

Frequently Asked Questions

What regex flavor does this use?

JavaScript (ECMAScript) regular expressions, which are supported natively in all modern browsers and in Node.js.

What do the flags g, i, m, and s mean?

g = global (find all matches), i = case-insensitive, m = multiline where ^ and $ match line boundaries, s = dotAll where the dot character matches newlines too.

How do I match a literal dot or bracket?

Escape special characters with a backslash: \. matches a literal dot, \[ matches a literal opening bracket.

Why does my regex work in Python but not here?

Different languages use different regex engines. Python uses PCRE which supports features like variable-length lookbehinds that standard JavaScript regex does not support.

What does the capture-group summary show?

When your pattern contains capture groups, a summary below the match list reports how many times each numbered group (and each named group, annotated with its name) actually captured across all matches — useful for catching optional groups that never fire.

About Regex Tester

How it Works

1Type your pattern and toggle the flags you need (g, i, m, s, u).

2Paste sample text — matches highlight immediately and a capture-group breakdown shows how often each numbered or named group fires.

3Switch to the Replace tab and type a replacement string; the preview re-renders on every keystroke (use $1, $2 for numbered groups).

4Open Export code to copy an equivalent snippet in JavaScript, Python, Java, or Go.

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About Regex Tester

How it Works

Frequently Asked Questions

About Regex Tester

How it Works

Frequently Asked Questions