Regex to English Explainer

Paste a regular expression and get a plain-English, step-by-step reading of what it matches — anchors, character classes, quantifiers, groups, lookarounds and backreferences — indented the same way the pattern is nested. It reads JavaScript (ECMAScript) syntax, which shares most of its notation with PCRE, Python and Java, and you can try the pattern on a test string straight away.

How to use this tool

1. Paste the pattern, either bare (\d+) or as a literal with slashes (/\d+/gi).
2. Add flags if they are not already in the literal.
3. Optionally type a test string to see what the pattern matches.
4. Press Calculate. Read the explanation from top to bottom; indented lines belong to the group above them.

Formula

* = 0 or more · + = 1 or more · ? = 0 or 1 · {n} = exactly n · {n,} = n or more · {n,m} = n to m

A quantifier applies only to the item directly before it — one character, a class, an escape or a whole group. Adding ? after a quantifier (*?, +?) makes it lazy, so it takes as few characters as possible. Calculation runs in a worker with a two-second limit.

Example

The default date pattern reads as: the start of the string; capturing group 1 named "year" — a digit, exactly 4 times; the character "-"; capturing group 2 named "month" — either "0" followed by one character from [1 to 9], or "1" followed by one character from [0 to 2]; another "-"; group 3 named "day" — a digit, exactly 2 times; then the end of the string. It reports 3 capturing groups, and the test string 2026-10-29 gives 1 match.