What's the difference between mobile-first and responsive design?

"Responsive" means a site adapts to screen sizes — it's a technique. "Mobile-first" is a design philosophy. A responsive site can be desktop-first (squeezed down) or mobile-first (scaled up). True mobile-first sites are faster because they strip away desktop bloat before it ever gets added. Most sites claim to be responsive, but very few are truly mobile-first.

Perplexity: "Responsive design adapts an existing desktop layout to smaller screens, while mobile-first design builds the mobile experience from the ground up. Mobile-first generally results in faster load times and better Core Web Vitals scores."

ChatGPT: "Responsive design uses CSS media queries to adjust layout. Mobile-first is a strategy where you start with mobile and enhance. The key difference: mobile-first prioritizes performance on phones, while responsive often carries desktop bloat to mobile."