Claude Design MCP

Claude Design MCP turns Claude Code into a persistent design studio. It gives Claude MCP tools for generating HTML/CSS designs, iterating on them, comparing variants, rendering screenshots, extracting reusable design systems, and exporting Google DESIGN.md files.

It is not a thin prompt wrapper. Designs are saved as plain HTML on disk, indexed in SQLite, lineage is preserved, screenshots can be rendered through Playwright, and every model call is routed through the local Claude Code OAuth session instead of an Anthropic API key.

What You Get

Capability	What it does
Persistent designs	Stores every design as a browsable .html file under a local studio directory.
Iteration history	Keeps parent/child lineage so agents can refine a design without losing the original.
Parallel variants	Fans out multiple takes across mood, layout, palette, density, or any other dimension.
Screenshot rendering	Uses Playwright to render mobile, tablet, desktop, wide, and HD PNGs.
Contact-sheet preview	Builds a local gallery of the studio so designs can be compared quickly.
Design-system extraction	Distills tokens, components, principles, and optional Google DESIGN.md output.
Safe export	Packages designs or systems as portable folders and zip files.
First-contact demo	Creates local fixture designs without spending OAuth/model calls.

Quick Start

Prerequisites:

• Python 3.10 or newer.
• uv for local tool installation.
• Claude Code installed and logged in with OAuth.

From PyPI (recommended once v0.2.0 is published):

claude login
uv tool install "claude-design-mcp[render]" --with-executables-from playwright
playwright install chromium

claude mcp add --scope user claude-design -- claude-design-mcp
claude-design-mcp --check-json
claude-design-mcp --demo

From source (current path until the PyPI release lands):

git clone https://github.com/Evilander/claude-design-mcp.git
cd claude-design-mcp

claude login
uv tool install ".[render]" --with-executables-from playwright
playwright install chromium

claude mcp add --scope user claude-design -- claude-design-mcp
claude-design-mcp --check-json
claude-design-mcp --demo

--check-json prints machine-readable readiness diagnostics for the Claude CLI, studio path, Playwright, temp directory, and browser payload. --demo creates three local demo designs without calling a model, which makes install validation cheap and repeatable.

Render extra: the [render] qualifier installs Playwright. --with-executables-from playwright exposes the playwright CLI used to install Chromium. Without [render], design generation and persistence still work; only screenshot rendering is disabled. --check-json reports this explicitly.

Using It From Claude

After registration, ask Claude Code for design work naturally:

• "Use claude-design to create a dashboard for a court calendar system, dense but calm."
• "Make 4 variants of this design: editorial, utilitarian, playful, and luxury."
• "Iterate on the second variant and make the empty state clearer."
• "Extract a design system from the last three designs and apply it to a checkout page."
• "Export a DESIGN.md from this system so another coding agent can use it."
• "Open the studio contact sheet."

MCP Tools

Tool	Purpose
design_create	Generate a self-contained HTML/CSS design from a brief.
design_iterate	Refine an existing design while preserving lineage.
design_variants	Generate parallel alternatives from a source brief or design.
design_render	Render a saved design to PNG at a named viewport.
design_preview	Build and open a local contact-sheet gallery.
design_extract_system	Extract tokens, components, and principles from one or more designs.
design_validate_design_md	Validate DESIGN.md output against Google's parser and lint rules.
design_apply_system	Create a new design constrained by an extracted system.
design_get	Fetch a design summary and optional HTML.
design_list	Browse saved designs with pagination and search.
design_export	Export a design or system as a folder plus zip archive.

Security Model

Model-authored HTML is treated as untrusted.

• Claude calls run through the local claude CLI with OAuth by default.
• ANTHROPIC_API_KEY, ANTHROPIC_AUTH_TOKEN, Bedrock, and Vertex env vars are scrubbed from Claude subprocesses unless CLAUDE_DESIGN_ALLOW_API_KEY=1 is set.
• Claude design calls use no tools, no slash commands, no session persistence, one turn, and isolated settings.
• Generated HTML is saved with a strict Content Security Policy.
• Inline scripts receive a fresh CSP nonce; model-authored nonces are stripped. Inline event handlers (onclick, onload, etc.) are blocked by the CSP via script-src 'nonce-...' + absence of 'unsafe-inline'.
• Persisted design HTML is capped at 2 MiB. Larger model output (e.g. prompt-injected base64 amplification) is refused at write time with a clear error.
• Playwright rendering disables JavaScript, blocks service workers, uses a fresh browser context, and aborts requests outside the local file plus approved image/font hosts.
• Export paths refuse traversal, symlink, junction, and reparse-point staging targets.
• Cwd .env files are ignored. Only an explicit CLAUDE_DESIGN_ENV_FILE is loaded, and only CLAUDE_DESIGN_* keys are accepted.

This setup still allows visual HTML/CSS exploration while making prompt-injected exfiltration paths much harder to reach.

DESIGN.md Export

Claude Design MCP can emit and validate Google DESIGN.md documents:

design_extract_system(format="design-md", source_ids=[...])
design_validate_design_md(design_md_path="...")

Use this when a visual direction should move from design exploration into implementation. DESIGN.md gives downstream coding agents stable tokens, component guidance, accessibility notes, and implementation constraints without copying giant HTML blobs through chat.

Scope in 0.2: export is one-way. We emit valid 8-section DESIGN.md and shell out to npx @google/design.md lint to validate it. Import (DESIGN.md -> SystemRecord -> design_apply_system) lands in 0.3 along with design_diff and region-pinned iterate. Track the roadmap in notes/ultraplan-2026-05-10/ship-claude-design-mcp.md.

Configuration

Env var	Default	Purpose
CLAUDE_DESIGN_MODEL	claude-sonnet-4-6	Fast-tier model for design calls.
CLAUDE_DESIGN_MODEL_OPUS	claude-opus-4-7	Best-tier model for deeper design calls.
CLAUDE_DESIGN_STUDIO_DIR	~/.claude-design/studio	Local studio root for designs, renders, exports, and SQLite index.
CLAUDE_DESIGN_AUTO_RENDER	auto	1, 0, or auto; controls screenshots after create/iterate.
CLAUDE_DESIGN_CLI_PATH	auto	Optional absolute path to the claude executable. Relative paths are refused.
CLAUDE_DESIGN_PLAYWRIGHT_TMP	auto	Writable temp directory for Playwright launch and download work.
CLAUDE_DESIGN_PLAYWRIGHT_BROWSERS_PATH	auto	Optional browser payload directory for local Playwright installs.
CLAUDE_DESIGN_CHROMIUM_SANDBOX	auto	auto, 1, or 0; controls Chromium sandbox fallback.
CLAUDE_DESIGN_EFFORT	low	Claude Code effort level. Use none to omit.
CLAUDE_DESIGN_THINKING	disabled	Thinking mode: disabled, adaptive, or none.
CLAUDE_DESIGN_MAX_BUFFER_BYTES	8388608	SDK stdout JSON buffer cap for large HTML responses.
CLAUDE_DESIGN_ALLOW_API_KEY	0	Set 1 to keep API-key, Bedrock, or Vertex auth env vars in the subprocess.
CLAUDE_DESIGN_ENV_FILE	unset	Optional explicit dotenv file. Only CLAUDE_DESIGN_* keys are loaded.

Manual Claude Desktop Config

Claude Code users should prefer claude mcp add. For manual MCP clients:

{
  "mcpServers": {
    "claude-design": {
      "command": "claude-design-mcp",
      "args": [],
      "env": {
        "CLAUDE_DESIGN_STUDIO_DIR": "${HOME}/.claude-design/studio"
      }
    }
  }
}

Project Layout

src/claude_design/
  server.py        MCP server and tool definitions
  designer.py      Claude Code OAuth call path and HTML extraction
  studio.py        Filesystem and SQLite persistence
  renderer.py      Playwright screenshot renderer
  design_md.py     DESIGN.md validation and emission helpers
  preview.py       Contact-sheet generation
scripts/
  smoke_mcp_stdio.py
tests/

The default studio lives at ~/.claude-design/studio and contains:

designs/      saved HTML documents
renders/      PNG screenshots
exports/      portable export folders and zips
designs.db    SQLite index with lineage and metadata
_index.html   optional contact sheet

Development

python -m pip install -e ".[dev,render]"
python -m ruff check src tests scripts
python -m pytest -q
python scripts\smoke_mcp_stdio.py
python -m build

Useful local checks:

$env:PYTHONPATH = "$PWD\src"
python -m claude_design --check-json
python -m claude_design --demo

Current Status

Claude Design MCP is beta software with a hardened local release path:

• OAuth-first auth path with explicit API-key opt-in.
• MCP stdio smoke coverage.
• Demo mode for model-free setup validation.
• CI for lint, tests, and build.
• Release workflow for tagged publishes.
• DESIGN.md extraction and validation.
• CSP, renderer, export, and dotenv hardening for untrusted model HTML.

License

MIT.