Mobile-First Design

Mobile-First Design is an approach that prioritizes designing for mobile devices before scaling up to larger screens like tablets or desktops. It focuses on delivering essential content and functionality on small screens, ensuring that the design is simple, fast, and responsive. Once the mobile version is optimized, it can be adapted for larger devices with additional features.

Mobile-first is more than a responsive design technique — it's a prioritization philosophy that forces you to decide what's truly essential. When you start with the constraints of a 375px screen, you can't include everything and must make hard decisions about hierarchy and core flows. Products designed desktop-first and then 'made responsive' typically have cluttered, cramped mobile experiences because they're trying to fit a desktop design into a mobile container rather than designing for mobile from scratch.

Twitter's mobile app is the primary product for most of their users, and their mobile-first approach means the core gestures (scroll, tap, swipe) are smooth and native, while the desktop web version has historically lagged in polish. The mobile product drives the product vision, not the other way around.