Bootstrap is the more common of the two in our index: it runs on 10,833 websites against 6,627 for Tailwind CSS, and 226 sites use both. Counts come from real scans, not vendor claims.
Bootstrap is a free and open-source CSS framework directed at responsive, mobile-first front-end web development. It contains CSS and JavaScript-based design templates for typography, forms, buttons, navigation, and other interface components.
Tailwind is a utility-first CSS framework for rapidly building custom user interfaces.
226 sites run both Bootstrap and Tailwind CSS. That is 3% of the sites using Tailwind CSS, 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.