Regex Tester & Debugger

What is Regex Tester & Debugger?

Our Regex Tester evaluates regular expressions against test strings in real time using the browser ECMAScript RegExp engine. Toggle standard regex flags (g, i, m, s, u), inspect capture group tables, highlight match index ranges, and test common patterns (emails, URLs, IPs) with zero network latency and complete privacy.

Designed for accuracy, speed, and privacy, this tool runs entirely on your local device with zero network latency.

How to Use the Regex Tester & Debugger

1. 1
   Enter your regular expression pattern into the pattern field (e.g., [a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,}).
2. 2
   Toggle your desired regex flags: g (global), i (case-insensitive), m (multiline), s (dotAll), or u (unicode).
3. 3
   Type or paste your test text in the test string area.
4. 4
   Inspect live highlighted match boxes and review extracted match indexes and capture group tables below.

Formula & Calculation Logic

Compiles regex strings using native JavaScript RegExp constructors. The matcher iterates through global match instances, extracting full matches, zero-indexed start/end offsets, and numbered capture groups.