What does Regex Debugger actually do?

The regex debugger steps through a JavaScript pattern against a sample so you can see which part failed. It is still the JS engine. It will not make an exponential pattern safe.

When should I use Regex Debugger?

Use it when the tester says “no match” and you cannot see why.

When should I not use Regex Debugger?

Do not debug a Python pattern here.

What does Regex Debugger not do?

Not a PCRE debugger. A hanging pattern can still hang the tab.

Regex Debugger

Step-by-step breakdown of how a regex matches: capture groups, named groups, lookahead/lookbehind. Free online — runs locally, no upload.

Pattern

$1year$2month$3day

Test String

Match Breakdown2 matches

Match #1 · chars 9–19

Full Match

2026-09-07

Capture Groups

$1 (year)2026

$2 (month)09

$3 (day)07

Match #2 · chars 36–46

Full Match

2026-09-08

Capture Groups

$1 (year)2026

$2 (month)09

$3 (day)08

Search tools

Regex Debugger