Is my test data sent to a server?

No. All regex matching happens locally in your browser using JavaScript's native RegExp engine. No data is transmitted.

Which regex flavor does this tool use?

This tool uses JavaScript's built-in RegExp engine, which supports ECMAScript regex syntax including lookaheads, lookbehinds, and named capture groups.

What are Regex flags?

Flags change how the regular expression behaves. For example, 'g' (global) finds all matches rather than stopping after the first, and 'i' (ignore case) makes the pattern case-insensitive.

What are capture groups?

Capture groups are created by wrapping part of your regex in parentheses '()'. They allow you to extract specific portions of a matched string, which this tool displays in the Match Details section.

Why is my regex not matching anything?

Common reasons include missing flags (like 'i' for case-insensitivity), unescaped special characters, or invisible whitespace in the test string. Use the Match Details section to debug piece by piece.

Regex Tester - Real-Time Pattern Matching

Test regular expressions with real-time highlighting. See matches, capture groups, and flags instantly. Free, private, client-side.

Pattern Matcher

lock Processing Locally

Regular Expression

/ /

Test String

The quick Brown Fox jumps over the Lazy Dog. Testing 123 and ABC patterns for regex matching.

Match Results

Matches will be highlighted here...

Matches

Groups

Chars Matched

Active Flags

info

About Regex Tester

Our Regex Tester is a free, client-side utility that lets you write regular expressions and instantly see matches highlighted in your test text. Because it runs entirely in your browser, you can safely test regex patterns against proprietary logs or sensitive data strings without any data leaving your machine.