Regex Tester Online — Test & Debug Regular Expressions Instantly

How to Use Regex Tester

1. Enter your regex pattern: Type your regular expression in the pattern field.
2. Set flags: Toggle flags such as global (g), case-insensitive (i), and multiline (m) as needed.
3. Paste test text: Enter the string you want to test against in the test area.
4. Review matches: Matching portions are highlighted in the test text and listed below with capture group values.

Features

• Real-time match highlighting as you type
• Shows all match positions and capture group values
• Supports global, case-insensitive, multiline, and other JS flags
• Displays match count and indices
• Runs entirely in your browser — no server calls
• Free with no account required

Common Use Cases

Developers use the regex tester when writing validation patterns for form inputs, parsing log files, extracting data from strings, or building search-and-replace scripts. It is much faster than writing test code in a local editor and running it.

Frequently Asked Questions

Which regex engine does the tester use?

The tester uses the JavaScript built-in RegExp engine, which follows the ECMAScript regular expression specification.

Can I test named capture groups?

Yes. JavaScript supports named capture groups using the (?<name>...) syntax, and the tester will display their values.

What does the global (g) flag do?

The global flag causes the regex to find all matches in the text rather than stopping after the first one.

Can I test lookaheads and lookbehinds?

Yes, as long as your browser supports them. Lookaheads and lookbehinds are supported in modern browsers including Chrome, Firefox, and Safari.

Related Tools