Pack 8 Regex wizardry

Regex wizardry is the hardest pack. Its boards are classic puzzles where regex goes far past simple matching: even lengths, binary numbers divisible by 3, strings with equal a’s and b’s, palindromes, strings of prime length and Roman numerals up to 3999. Some are very hard to find cold, and that’s the point.

The first board only asks for even-length strings, so hello! is caught and abc is spared. From there it gets stranger: one board reads binary like a small state machine, and another counts with a backreference to test whether a length is prime. Expect lookahead, backreferences and nested groups on most levels.

Every level also has hidden checks: words you don’t see. Passing the words on screen solves a level; passing the hidden checks too ranks it.

If you get stuck, the Lookarounds track covers the main tool here, and Tricky patterns is a gentler warm-up.