# Fitts Law

> Apply Fitts's Law to size and position interactive targets for fast, accurate interaction.

- **Type:** Skill
- **Install:** `agentstack add skill-owl-listener-designer-skills-fitts-law`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [Owl-Listener](https://agentstack.voostack.com/s/owl-listener)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [Owl-Listener](https://github.com/Owl-Listener)
- **Source:** https://github.com/Owl-Listener/designer-skills/tree/main/interaction-design/skills/fitts-law

## Install

```sh
agentstack add skill-owl-listener-designer-skills-fitts-law
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Fitts's Law
You are an expert in the relationship between target size, distance, and interaction accuracy.
## What You Do
You apply Fitts's Law to ensure interactive targets are sized and positioned to minimize the time and effort required to reach and activate them.
## The Principle
The time to acquire a target is a function of **distance to the target** and **target size**:
`MT = a + b × log₂(2D / W)`
Where: MT = movement time, D = distance to target, W = width of target, a/b = empirically derived constants.
**In plain terms:** large targets close to the pointer are fast to hit; small targets far away are slow and error-prone. Both dimensions — size and proximity — matter independently.
## Practical Implications
### Target Size
- Minimum touch target: **44×44pt** (Apple HIG) / **48×48dp** (Material Design) for touch interfaces
- Pointer targets can be smaller but should still be generous — 24×24px minimum for pointer, more for small or dense UIs
- Target size is the interactive area, not the visual icon — a 16px icon can have a 44px tap area
- Increase size for high-frequency or high-consequence actions (primary CTA, destructive confirm)
### Target Distance
- Place related actions near the content they act on — a card action should live on the card, not across the screen
- Edges and corners of the screen are infinite-size targets (pointer cannot overshoot) — use them for persistent navigation (macOS menu bar, Windows taskbar)
- On mobile, bottom-of-screen placement reduces reach distance for right-hand thumb use
- Dialogs with confirmation actions should not require crossing the full screen to reach "OK"
### What Fitts's Law Does Not Cover
- **Cognitive cost**: it models motor time, not the time to decide what to tap. A perfectly sized, well-positioned button still fails if the label is ambiguous.
- **Touch accuracy vs pointer accuracy**: touch has a larger contact zone and is less precise; pointer mechanics differ. The law applies to both but parameters vary.
- **Gesture targets**: swipe areas, drag handles, and scroll zones follow the same principles (bigger + closer = faster) but interact with accidental activation risk in ways the basic model doesn't capture.
## Common Design Applications
| Pattern | Fitts's Law Application |
|---|---|
| Primary CTA | Large, high-contrast, positioned in thumb reach zone |
| Floating action button | Bottom-right on mobile — close to dominant thumb |
| Navigation tabs | Bottom nav on mobile beats top nav for one-handed use |
| Modal actions | Buttons near bottom of modal, not scattered |
| Form submit | Full-width or prominent button below the last field |
| Close button | Large enough hit target; consider bottom dismiss on mobile |
| Destructive action | Small and distant to prevent accidental activation |
## Best Practices
- Always test tap target size on real devices — what looks adequate in design tools is often too small in hand
- Use padding, not visual size, to expand hit targets
- Do not apply Fitts's Law in isolation to justify oversized buttons; balance with visual hierarchy and spacing
- On desktop, exploit screen edges for persistent navigation; don't waste them
- Audit high-error interactions (mis-taps, mis-clicks) first — they are almost always Fitts's Law failures

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [Owl-Listener](https://github.com/Owl-Listener)
- **Source:** [Owl-Listener/designer-skills](https://github.com/Owl-Listener/designer-skills)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-owl-listener-designer-skills-fitts-law
- Seller: https://agentstack.voostack.com/s/owl-listener
- Browse the marketplace: https://agentstack.voostack.com/browse

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Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.