core-js is the more common of the two in our index: it runs on 17,404 websites against 347 for Tippy.js, and 194 sites use both. Counts come from real scans, not vendor claims.
core-js is a modular standard library for JavaScript, with polyfills for cutting-edge ECMAScript features.
Tippy.js is the complete tooltip, popover, dropdown, and menu solution for the web, powered by Popper.
194 sites run both core-js and Tippy.js. That is 56% of the sites using Tippy.js, the smaller of the two.
Want to know which one a particular site uses? Look it up and see its whole stack, or compare two sites side by side.