/blog/ · field notes from the hunt
/^key=[^=]*$/
key=valuekey=key=42key=on·key=a=bkeyvaluek=v
A 7-character pattern can take seconds on a 30-character input, and hours on a 40-character one. How backtracking works, why nested quantifiers like (a+)+ explode, the outages it caused at Stack Overflow and Cloudflare, and the rewrites that make a pattern safe.
Regex Hunter/^(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})$/
2026-10-131999-12-312000-01-012026-02-28·26-10-132026/10/132026-1-313-10-2026
Parentheses do two jobs: they group and they capture. How non-capturing groups (?:…) group without capturing, how named groups (?<year>…) make captures readable, how to refer back to them with \k<name>, and how Python spells it.
Regex Hunter/^colou?r$/i
colorColourCOLORcolour·colrcoloursdiscolorkolor
What each JavaScript regex flag changes, with live examples: case-insensitive i, global g (and the lastIndex trap), multiline m, dotAll s, unicode u, sticky y and indices d, plus how Python spells the same ideas.
Regex Hunter/^\d{5}$/
90210100010213960614·9021902100ZIP 9021090210-1234
^ and $ don't match characters, they match positions. Why a pattern without anchors checks less than you think, what the m flag changes, how Python's $ treats a trailing newline, and when to use \A and \z instead.
Regex Hunter/^[A-Z][a-z]+$/
ParisLimaOsloRome·parisPARISNew YorkR2D2
Character classes are the most-used part of regex and the easiest to get subtly wrong. What [abc], [a-z], [^…], \d, \w and \s really match, and the traps behind them: [A-z], the stray hyphen, the dot inside brackets, and digits that aren't 0 to 9.
Regex Hunter/<.+?>/
<b></i><br>·bi><>
Regex quantifiers grab as much text as they can. Here's how greedy and lazy matching really work, why <.+> swallows a whole line of HTML, and when a negated class beats both.
Regex HunterToday’s board is live
Match every monster, spare every innocent — in as few characters as you can.