Regex Tester - Real-Time Pattern Matching
Test JavaScript regular expressions with live match highlighting, capture groups and g/i/m/s flags. A free, private regex tester that runs in your browser.
Pattern Matcher
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.
Features
- Real-time match highlighting as you type
- Toggle flags: global, case-insensitive, multiline, dotAll
- Capture group extraction and display
- 100% client-side — safe for sensitive data
How to Use
- Type your regular expression in the pattern field
- Toggle the flags (g, i, m, s) as needed
- Enter or paste your test string below
- Matches are highlighted instantly in the results panel
Frequently Asked Questions
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.