Pattern Hunter

You get two word lists: must-match (green) and must-not-match (red). Type one regular expression that matches every green word and none of the reds. The words light up live as you type. Once it separates them, shorten your pattern to beat the par length.

• Your pattern is tested against each word; add anchors yourself if you need them
• Match all greens, reject all reds, then golf the length down
• Score rewards a short pattern that comes in under par

• Desktop: type your pattern in the input and press Enter or Submit; Reveal shows an example solution
• Phone & tablet: tap the input and type with the on-screen keyboard

• Difficulty: Easy, Medium or Hard word sets
• Daily for a shared puzzle, Practice for an endless stream

• Hunt for a substring or character class the greens share and the reds lack, often two or three characters is enough
• Reveal gives a working example; treat its length as the target to undercut

Pattern Hunter is regex golf, a code-golf puzzle about expressive, minimal pattern matching.

• Skills: regular expressions, pattern matching, concise problem-solving
• Best for: roughly grades 9–12 (ages 14+)
• For parents & teachers: concise, expressive pattern matching.

Writing one regular expression that matches every word on a green list and none on a red one is the real task the notation exists for: describing a set of strings precisely.

The two lists are doing the work of a specification. Without the red list any pattern that matches everything would pass, which is the commonest way a real regex goes wrong.

That tension between too permissive and too strict is the whole craft, and it is why the Kleene star — match any number of these, including none — is both the notation's most useful operator and the one that causes the most accidents.

Pattern Hunter is regex golf: a code-golf puzzle about expressive, minimal pattern matching. It is an original, free browser game built in-house for PlayPendium.

A free, original browser game on PlayPendium. No download, no install.