What is the difference between a greedy and a lazy quantifier?

A greedy quantifier such as * or + matches as much as possible, then backtracks. Adding a ? makes it lazy (such as *? or +?), so it matches as little as possible while still allowing the overall pattern to succeed.

What does a lookahead do?

A lookahead asserts what follows without consuming it. (?=abc) is a positive lookahead matching only if abc follows; (?!abc) is a negative lookahead matching only if abc does not follow. Lookbehinds, (?<=abc) and (?<!abc), assert what precedes.

Is any data sent anywhere?

No — this is a static reference that runs entirely in your browser. Nothing is uploaded.

Regex Syntax Reference

Q: Is any data sent anywhere?

No — this is a static reference that runs entirely in your browser. Nothing is uploaded.

Searchable cheat sheet of regular-expression tokens, quantifiers and flags.

Regex syntax reference

A searchable cheat sheet for regular expressions — character classes, anchors, quantifiers, groups, alternation, lookaround and flags — each with a plain-English meaning. Syntax follows the common JavaScript / PCRE conventions.

Type a token or keyword — for example digit, lookahead or quantifier — to filter the list. Everything runs in your browser.