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Universal Design Principles
A cross-agent skill marketplace of 42 framework-agnostic UX & product-design principles, drawn from Universal Principles of Design (Lidwell, Holden, Butler, 2003) and the broader design and HCI research literature.
Getting Started · Architecture · Principle Index · How Skills Trigger · Attribution · Contributing
What this is
A working library of design principles, packaged as portable Agent Skills plus native plugin metadata for Claude Code, Codex, and Cursor. Install one or more plugins and your agent gains access to curated skills that fire automatically whenever you work on UX, UI, or product design — regardless of design system, SDK, framework, or platform.
Each principle is built as a reference-grade entry: a router-style SKILL.md (~350–500 lines), 2–4 sub-aspect skills for context-specific application (~200–300 lines each), and per-skill references/ deep-dive files with origins, research lineage, and worked patterns. The result is a library an agent can apply with the same depth as a senior designer who has internalized the canon.
Why a plugin marketplace?
Many products today are built and reviewed by AI agents. The quality of their design judgment depends heavily on what they've been taught to attend to. Without a working library of principles, an agent will produce designs that are competent on average but blind in specific ways — the typography will drift, hierarchy will collapse on the third screen, the error states will be afterthoughts, the interaction patterns will be inconsistent across surfaces.
This marketplace gives your agent the same canon that experienced designers have internalized over years. Instead of one giant prompt, the canon is split across five composable plugins so you can install only what you need:
| Plugin | What it teaches | Skills |
|---|---|---|
| Perception & Hierarchy | How the eye groups elements, where it lands first, what makes a composition read as ordered | 34 |
| Cognition & Learnability | Mental models, complexity reduction, memory load, how new users get oriented | 33 |
| Interaction & Control | Affordance, feedback, errors, user agency, Fitts's Law for touch targets | 29 |
| Aesthetics & Emotion | Beauty, perceived quality, brand voice, flow, persuasive form | 17 |
| Process & Robustness | Iteration, accessibility, reliability under stress, what to prune | 24 |
Each plugin contains a router skill (which triggers on the plugin's category and points the agent at the right principle), one main skill per principle, and 2–4 sub-aspect skills for principles whose application varies meaningfully by context (e.g., Hick's Law has different shapes in menus vs. defaults vs. pricing).
Installation
Pick the agent you actually use. The same skills/<skill-name>/SKILL.md folders are the source of truth for every install path; only the plugin manifest or destination directory changes.
| Agent | Best install path | This repo provides |
|---|---|---|
| Claude Code | Native plugin marketplace | .claude-plugin/marketplace.json and per-plugin .claude-plugin/plugin.json |
| Codex | Native plugin marketplace, or direct Agent Skills | .agents/plugins/marketplace.json and per-plugin .codex-plugin/plugin.json |
| Cursor | Cursor plugin flow, or project rules fallback | .cursor-plugin/marketplace.json and per-plugin .cursor-plugin/plugin.json |
| Gemini CLI | Link or copy Agent Skills | Plain skills/*/SKILL.md folders |
| Copilot, Windsurf, and other agents | Native rules or AGENTS.md fallback | Portable skill folders plus a compact rule/instruction pattern |
The packaging follows the Agent Skills open format, where each skill is a folder containing SKILL.md and optional supporting files.
Claude Code
In Claude Code, add this repository as a plugin marketplace and install the plugins you want:
