Design Harness for Claude Code

A 3-layer design system for engineers who want to ship great UI without being designers. Based on Neethan Wu's "Design Without Designing".

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Layer 1 — Skills (the expertise)

Skills are instruction files that load design expertise into your agent. This plugin bundles 6 of them.

Bundled in this plugin

Skill	Invoke	What it does
emil-design-eng	/emil-design-eng	Emil Kowalski's animation & UI polish philosophy. Review table format, spring physics, clip-path tricks, performance rules.
baseline-ui	/baseline-ui	Tailwind constraints, accessible primitives, animation rules. Catches AI-generated slop.
fixing-accessibility	/fixing-accessibility	ARIA, keyboard nav, focus traps, WCAG audit.
fixing-metadata	/fixing-metadata	OG tags, canonical URLs, SEO, social card audit.
fixing-motion-performance	/fixing-motion-performance	Compositor-only animation, layout thrash prevention, scroll perf.
interface-design	/interface-design	Intent-first design system. Domain exploration, signature elements, surface elevation, craft checks.

Sources: emilkowalski/skill · ibelick/ui-skills · Dammyjay93/interface-design

Also install separately

Impeccable (pbakaus/impeccable) — 20+ commands including /delight, /polish, /audit, /animate, /typeset, /arrange. The most-used skill in the harness.

/plugin add impeccable@impeccable

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Layer 2 — Agent Canvas (the surface)

Design surfaces that use your agent as the kernel. No built-in AI — they expose MCP tools and let Claude do the work.

Pencil

Git-diffable .pen format. Design files live in your repo, versioned like code. Supports agent swarm mode (up to 6 agents working on the canvas simultaneously).

• Install: pencil.dev — free
• MCP: Installed via the Pencil desktop app (auto-registers MCP server)
• Permission: already added to settings.json → permissions.allow: ["mcp__pencil"]

Paper

HTML/CSS canvas — what you design is actual code, no translation layer. MCP exposes full read/write to design files.

• Install: paper.design — free tier available
• MCP: Runs locally when the Paper desktop app is open with a file

# Already added to your Claude Code user config:
claude mcp add paper --transport http http://127.0.0.1:29979/mcp --scope user

Paper MCP starts automatically when you open a .paper file in the desktop app. If tools stop responding, restart the agent session to re-establish the connection.

Available Paper MCP tools: get_basic_info, get_selection, get_node_info, get_children, get_tree_summary, get_screenshot, get_jsx, get_computed_styles, create_artboard, write_html, set_text_content, rename_nodes, duplicate_nodes, update_styles, delete_nodes

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Layer 3 — Inspiration (the eye)

Tools for training visual taste. Use before design work to calibrate what "good" looks like.

Tool	URL	What it does
Variant	variant.ai	Type an idea → endless non-repeating design interpretations. Style Dropper absorbs visual DNA from any design and transfers it. Export as React or copy prompts with HTML references for your coding agent.
Mobbin	mobbin.com	Curated mobile + web UI patterns from top apps. Best for onboarding, settings, checkout flows. Figma plugin available.
Awwwards	awwwards.com	Jury-scored cutting-edge web craft. Raises the ceiling for what's possible.
Cosmos	cosmos.so	Visual inspiration board. Hex color search, vague description search, curated collections. Web, interiors, typography, photography.

Workflow: Spend ~20 minutes in Variant or Cosmos before any design session. Build clusters of visual references. Then prompt your agent with specific references or export Variant components directly to code.

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How the layers work together

Inspiration (Layer 3)
  ↓ calibrates taste, gives references
Skills (Layer 1)
  ↓ encode expertise, enforce quality
Agent Canvas (Layer 2)
  ↓ Claude executes with real tools
→ shipped design

1. Open Variant or Cosmos, find a direction that fits your product
2. Open Pencil or Paper with a design file
3. Invoke the right skill for the task:
   • Starting fresh → /interface-design (domain exploration + intent)
   • Polishing existing UI → /delight or /polish (Impeccable)
   • Reviewing animations → /emil-design-eng
   • Checking a11y → /fixing-accessibility
   • Auditing overall → /audit (Impeccable)
4. Let Claude work on the canvas via MCP
5. Export code directly — no handoff

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Credits

• Neethan Wu — the harness concept
• Emil Kowalski — design engineering skill
• Julien Thibeaut — UI Skills
• Oyindamola Akinleye — Interface Design
• Paul Bakaus — Impeccable