halloween.js is a free, zero-dependency library that adds Halloween-themed ambient effects to any website: blinking eyes, flying witches, a dropping spider, a rising tombstone, and spider webs in the screen corners. Turn it on with a single CSS class on , then opt into individual effects with modifier classes. No JS call required. Works via npm or a single CDN script tag, no build step needed. Under 10 KB gzipped, MIT licensed, completely free.