GroundRules: Skill for Claude Code

Apple Design

How Apple builds interfaces that stop feeling like a computer and start feeling like an extension of you. This knowledge comes from Apple's WWDC design talks — chiefly Designing Fluid Interfaces (WWDC 2018) — distilled and translated into the web platform (CSS, Pointer Events, requestAnimationFrame, spring libraries like Motion/Framer Motion).

The through-line: an interface feels alive when motion starts from the current on-screen value, inherits the user's velocity, projects momentum forward, and can be grabbed and reversed at any instant. Springs are the tool that makes all of this natural, because they are inherently interruptible and velocity-aware.

The Core Idea

"When we align the interface to the way we think and move, something magical happens — it stops feeling like a computer and starts feeling like a seamless extension of us."

An interface is fluid when it behaves like the physical world: things respond instantly, move continuously, carry momentum, resist at boundaries, and can be redirected mid-motion. Everything below is a way to get closer to that.

Apple frames design as serving four human needs: safety/predictability, understanding, achievement, and joy. Every rule here serves one of them.

1. Response — kill latency

The moment lag appears, the feeling of directness "falls off a cliff." Response is the foundation everything else is built on.

• Respond on pointer-down, not on release. Highlight a button the instant it's pressed. Waiting for click/touch-up to show feedback feels dead.
• Be vigilant about every latency. Audit debounces, artificial timers, transition waits, and the ~300ms tap delay. Anything on the input path that isn't essential is a regression.
• Feedback must be continuous during the interaction, not just at the end. For a drag, slider, or drawer, update the UI 1:1 with the pointer the whole way through — never animate only when the gesture completes.

/* Feedback lives on the press, and it's instant */
.button:active {
  transform: scale(0.97);
  transition: transform 100ms ease-out;
}