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fitts-law-screen-edges

Use this skill when designing for the edges and corners of the screen — where the cursor cannot overshoot, making them effectively infinite-sized targets along one axis. Trigger when designing global navigation, system menus, sticky headers, fixed sidebars, full-bleed CTAs, or anywhere you can put the most-frequent or hardest-to-find actions. Trigger when reviewing an app that has wasteful margins on every side and asks the user to aim for tiny targets in the middle. Sub-aspect of `fitts-law`; read that first if you haven't already.

plugins/HDeibler/universal-design-principles/plugins/interaction-and-control-principles/skills/fitts-law-screen-edges/SKILL.md

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# Fitts's Law and the screen edge

The screen edge is the most undervalued real estate in modern web UI. Because the cursor cannot move past the edge, an element placed flush against an edge is effectively *infinite* in size along the axis perpendicular to that edge — the user can fly the cursor past the screen boundary and the cursor stops on the target without precision.

## Why edges matter

The Fitts's Law equation depends on target width along the axis of motion:

```
T = a + b · log₂(D / W + 1)
```

When `W` approaches infinity, the log term collapses to nearly zero — the only remaining cost is the constant base time. This is why Mac's menu bar at the top edge is faster to acquire than a menu in a window: the cursor can fly upward without ever overshooting.