I built a a 3KB alternative to replace zxcvbn (389KB) without detection loss

zxcvbn is the most widely used password strength estimator with 1M npm downloads a week. It's also 389KB gzipped and hasn't shipped a commit since 2017. Most sign-up forms are hauling that around just to block password123 . Poor password UX is a real conversion problem. A strength meter that adds 389KB to your bundle delays page load — on mobile, measurably so. Users who hit a slow registration page don't wait. They leave. The irony is that most of that weight goes toward catching passwords nobody is actually using to register on your site. So I built passcore - 3.0KB gzipped and 98.4% detection rate on real breach data - same as zxcvbn, benchmarked against a deduped list of passwords pulled live from RockYou, Adobe, HIBP, and other major leak lists. zxcvbn takes ~9.7ms to load — it's parsing 389KB of dictionary into memory on every cold start. passcore loads in ~0.2ms. It evaluates a password in ~2,600 nanoseconds. For a registration form, it's effectively invisible — no jank, no layout shift, no contribution to your Core Web Vitals score. The strength meter shows up before the user finishes typing their first character. How it works: passcore runs five detection layers on every password: Dictionary - All entries sourced directly from breach data, not a generic word list Keyboard patterns - qwerty , asdf , 1234 , numpad walks Repeats - aaaa , ababab Sequences - abcdef , 123456 L33t speak - decodes p@ssw0rd → password , m0nk3y → monkey , then dictionary lookup The dictionary is small by design. Every entry was chosen because it appears in real breach data - not because it's a common English word. Password1! is caught not by a 40k word list but by stripping the suffix and checking if the core word is in the breach list. It is. The scoring model: passcore returns a score from 0 to 4 - same scale as zxcvbn. The detection layers run first. A dictionary match, keyboard pattern, repeat, sequence, or l33t substitution scores 0 or 1 immediately - no further calculation. If