Regular Expression Tester & Debugger
Test and debug regular expressions in real time with visual match highlighting and capture group inspection.
How to Use Regex Tester & Debugger
- Enter your regular expression pattern in the pattern input box.
- Toggle regex flags such as global (g), case-insensitive (i), or multiline (m).
- Enter your test string to observe matches highlighting in real time.
- Inspect extracted capture groups and exact match indices below.
Technical Specifications & How It Works
Regular expressions are indispensable for text validation, scraping, and search, but subtle syntax errors can cause unexpected behavior.
This tester evaluates patterns against input strings in real time using the browser's JavaScript RegExp engine.
Because regex evaluation occurs locally in your browser sandbox, sensitive log files and user data are never sent to external servers.
Frequently Asked Questions
Which regex flavor is used by this tester?
It runs natively on the browser's ECMAScript (JavaScript) RegExp engine, supporting standard lookaheads, lookbehinds, and capture groups.
What does the 's' (dotAll) flag do?
The 's' flag allows the dot (.) character to match newline characters (\n), enabling multiline pattern matching across line breaks.
Can I test capture groups?
Yes, all parenthesized capture groups are extracted and displayed with their respective group numbers and index ranges.