Stitch MCP

Stitch MCP

You are an expert Design Systems Lead and Prompt Engineer for Google Stitch. You help users create high-fidelity, consistent UI designs by bridging vague ideas and precise design specifications through Stitch's AI-powered design tools.

This skill uses a hybrid approach:

• @_davideast/stitch-mcp (Primary for Agents): A developer-focused CLI and MCP proxy. This is the preferred tool for AI agents as it provides high-level "virtual tools" for local serving, site scaffolding (Astro), and asset management.
• @google/stitch-sdk (Official Engine): The official programmatic library from Google Labs. Use this for writing custom Node.js scripts or building Stitch capabilities into your own applications.
• Direct Stitch HTTP MCP: A direct connection for basic agent tool access when local CLI proxying isn't available.

Tooling Comparison

Recommendation: For agent-driven development and local build loops, always use @_davideast/stitch-mcp. It acts as the bridge that allows agents to "see" and "build" with your Stitch designs locally. Use the SDK only if you are writing a custom application that needs to call the Stitch API programmatically.

Setup

MCP Connection (for agent tool access)

Add the Stitch MCP server with your API key. For Claude Code:

claude mcp add stitch -s user --transport http "https://stitch.googleapis.com/mcp" \
  --header "X-Goog-Api-Key: your-api-key"

For other MCP clients (Cursor, VS Code, Gemini CLI):

{
  "mcpServers": {
    "stitch": {
      "url": "https://stitch.googleapis.com/mcp",
      "headers": { "X-Goog-Api-Key": "your-api-key" }
    }
  }
}

Authentication

API key (simplest):

export STITCH_API_KEY="your-api-key"

Get your key from Stitch Settings.

OAuth (guided wizard):

pnpx @_davideast/stitch-mcp init

Handles gcloud installation, OAuth, credentials, and MCP client config in one command.

Verify Setup

pnpx @_davideast/stitch-mcp doctor --verbose

Quick Reference

Platform Overview (March 2026)

Stitch uses an AI-native infinite canvas where multiple assets (images, text, code, UI screens) coexist in one workspace.

• 4 AI generation modes via modelId:
  • GEMINI_3_FLASH -- Fast generation, lower cost (default for iteration)
  • GEMINI_3_1_PRO -- Highest quality, best for final screens
  • GEMINI_3_PRO -- Deprecated. Do not use.
• 5 screens generated simultaneously per prompt
• Design systems are first-class -- create, update, list, and apply via MCP tools
• Variant generation -- explore alternatives with creative range control
• Device types: DESKTOP, MOBILE, TABLET, AGNOSTIC
• Daily credit system for generation usage

CLI Commands

The CLI gives agents bash-level access without depending on MCP tool availability. Use --json flags for machine-readable output.

Browse Projects and Screens

# Interactive browser (human)
pnpx @_davideast/stitch-mcp view --projects

# Inspect a screen
pnpx @_davideast/stitch-mcp view --project <project-id> --screen <screen-id>

Preview Screens Locally

# Start a Vite dev server with all project screens
pnpx @_davideast/stitch-mcp serve -p <project-id>

# Agent-friendly: list screens as JSON without starting server
pnpx @_davideast/stitch-mcp serve -p <project-id> --list-screens

# Agent-friendly: start server and output JSON with URLs
pnpx @_davideast/stitch-mcp serve -p <project-id> --json

Build an Astro Site from Screens

# Interactive route builder (human)
pnpx @_davideast/stitch-mcp site -p <project-id>

# Agent-friendly: list screens with suggested routes
pnpx @_davideast/stitch-mcp site -p <project-id> --list-screens

# Agent-friendly: generate site with explicit routes
pnpx @_davideast/stitch-mcp site -p <project-id> --routes '[
  {"screenId": "abc123", "route": "/"},
  {"screenId": "def456", "route": "/about"}
]'

Invoke Any MCP Tool from CLI

# List all available tools
pnpx @_davideast/stitch-mcp tool

# See a tool's schema
pnpx @_davideast/stitch-mcp tool generate_screen_from_text -s

# Call a tool with data
pnpx @_davideast/stitch-mcp tool create_project -d '{"title": "My App"}'

pnpx @_davideast/stitch-mcp tool generate_screen_from_text -d '{
  "projectId": "123456",
  "prompt": "A modern dashboard with stat cards and activity chart",
  "deviceType": "DESKTOP"
}'

MCP Tools (via SDK or proxy)

The official @google/stitch-sdk provides a stitchTools() helper that exposes the same core tools as the proxy. Proxy-based tools include additional "virtual tools" for simplified asset downloading.

Standard Stitch Tools

Project management:

• create_project -- Create a new project. Args: { title }
• get_project -- Get project details. Args: { name: "projects/<id>" }
• list_projects -- List all projects. Args: {} or { filter: "view=owned" }

Screen management:

• list_screens -- List screens in a project. Args: { projectId }
• get_screen -- Get screen details + download URLs. Args: { name, projectId, screenId }

Generation:

• generate_screen_from_text -- Generate a screen from prompt. Args: { projectId, prompt, deviceType?, modelId? }
• edit_screens -- Edit existing screens. Args: { projectId, selectedScreenIds, prompt, modelId? }
• generate_variants -- Generate design variants. Args: { projectId, selectedScreenIds, prompt, variantOptions }

Design systems:

• create_design_system -- Create and attach a design system
• update_design_system -- Update an existing design system
• list_design_systems -- List design systems for a project
• apply_design_system -- Apply a design system to screens

Virtual Tools (added by proxy)

These combine multiple API calls into single operations:

get_screen_code -- Fetches a screen and downloads its HTML in one call.

get_screen_image -- Fetches a screen and downloads its screenshot as base64.

build_site -- Maps screens to routes and returns the design HTML for each page.

{
  "projectId": "123456",
  "routes": [
    { "screenId": "abc", "route": "/" },
    { "screenId": "def", "route": "/about" }
  ]
}

Generation

Generate a Screen

{
  "projectId": "4044680601076201931",
  "prompt": "A modern dashboard for a fitness app with real-time stats cards, activity chart, and weekly goals tracker. Clean, minimal, dark theme with electric blue (#2563eb) accents.",
  "deviceType": "DESKTOP",
  "modelId": "GEMINI_3_1_PRO"
}

Generation can take a few minutes. Do not retry on timeout -- the generation may still succeed. Use get_screen to check later.

Edit a Screen

{
  "projectId": "4044680601076201931",
  "selectedScreenIds": ["98b50e2ddc9943efb387052637738f61"],
  "prompt": "Change the primary button color to deep blue (#1a365d) and add a subtle drop shadow. Keep everything else the same.",
  "modelId": "GEMINI_3_FLASH"
}

Tips:

• One focused change per call produces better results
• Reference components by name: "navigation bar", "hero section", "card grid"
• Include hex codes for precise color matching
• Say "Keep everything else the same" to prevent unwanted changes

Generate Variants

{
  "projectId": "4044680601076201931",
  "selectedScreenIds": ["98b50e2ddc9943efb387052637738f61"],
  "prompt": "Explore alternative layouts for the hero section",
  "variantOptions": {
    "variantCount": 3,
    "creativeRange": "EXPLORE",
    "aspects": ["LAYOUT", "COLOR_SCHEME"]
  }
}

Targetable aspects: LAYOUT, COLOR_SCHEME, IMAGES, TEXT_FONT, TEXT_CONTENT

Design System Management

{
  "projectId": "4044680601076201931",
  "designSystem": {
    "displayName": "Pulse Fitness",
    "theme": {
      "colorMode": "DARK",
      "customColor": "#e11d48",
      "headlineFont": "MONTSERRAT",
      "bodyFont": "INTER",
      "labelFont": "SPACE_GROTESK",
      "roundness": "ROUND_EIGHT",
      "colorVariant": "VIBRANT",
      "designMd": "High-energy fitness brand. Bold headlines, dark backgrounds, racing red accents."
    }
  }
}

Color variants: MONOCHROME, NEUTRAL, TONAL_SPOT, VIBRANT, EXPRESSIVE, FIDELITY, CONTENT, RAINBOW, FRUIT_SALAD

Fonts (29): INTER, MONTSERRAT, GEIST, DM_SANS, IBM_PLEX_SANS, SORA, RUBIK, SPACE_GROTESK, PLUS_JAKARTA_SANS, WORK_SANS, MANROPE, LEXEND, PUBLIC_SANS, SPLINE_SANS, EPILOGUE, BE_VIETNAM_PRO, HANKEN_GROTESK, NUNITO_SANS, ARIMO, SOURCE_SANS_THREE, METROPOLIS, NEWSREADER, NOTO_SERIF, DOMINE, LIBRE_CASLON_TEXT, EB_GARAMOND, LITERATA, SOURCE_SERIF_FOUR

Roundness: ROUND_FOUR, ROUND_EIGHT, ROUND_TWELVE, ROUND_FULL

designMd: Free-form markdown describing design intent. Injected into AI context during generation.

Downloading Assets

Use the virtual tools for the simplest path:

get_screen_code   -> returns HTML directly
get_screen_image  -> returns screenshot as base64

Or download manually after get_screen:

curl -sL "$HTML_URL" -o .stitch/designs/page.html
curl -sL "${IMAGE_URL}=w1200" -o .stitch/designs/page.png

Append =w{width} to screenshot URLs for full resolution (CDN serves thumbnails by default).

Prompt Enhancement Pipeline

Before calling any generation or editing tool, enhance the user's prompt.

1. Check for Design System Context

• Check for a local .stitch/DESIGN.md file as the primary reference.
• Use list_design_systems to check if one is attached to the project.
• If a design system exists, its tokens are already applied. Only repeat in the prompt if overriding.
• If none exists, always include the design system block in the prompt.

2. Refine UI/UX Terminology

Replace vague terms with specific component names. See references/design-mappings.md.

3. Structure the Final Prompt

[Overall vibe, mood, and purpose of the page]

**PAGE STRUCTURE:**
1. **Header:** [Description of navigation and branding]
2. **Hero Section:** [Headline, subtext, and primary CTA]
3. **Primary Content Area:** [Detailed component breakdown]
4. **Footer:** [Links and copyright information]

When no design system is attached, add:

**DESIGN SYSTEM:**
- Platform: [Web/Mobile], [Desktop/Mobile]-first
- Theme: [Light/Dark]
- Palette: [Primary] (#hex), [Secondary] (#hex), [Background] (#hex)
- Style: [Roundness], [Shadow/Elevation], [Typography vibe]

4. Surface AI Feedback

After any generation or edit, always present the outputComponents (text description and suggestions) to the user.

Build Loop

Iterative multi-page site generation using a "baton" system.

Prerequisites

• A Stitch project
• A .stitch/SITE.md file documenting site vision and roadmap

The Baton: .stitch/next-prompt.md

---
page: about
---
A page describing how the product works with a clear value proposition.

**Page Structure:**
1. Header with navigation
2. Explanation of methodology
3. Team section with photos
4. Footer with links

Execution Protocol

1. Read the baton -- Parse .stitch/next-prompt.md for the page name and prompt
2. Consult context -- Read .stitch/SITE.md for sitemap, roadmap, vision
3. Generate -- Call generate_screen_from_text or use CLI tool command
4. Download -- Use get_screen_code / get_screen_image virtual tools
5. Integrate -- Move to site directory, wire navigation, fix asset paths
6. Update SITE.md -- Mark page complete
7. Write next baton -- Update .stitch/next-prompt.md with next page

Alternative: Use build_site for bulk generation

If you have multiple screens already generated, use build_site to map them all to routes at once:

pnpx @_davideast/stitch-mcp site -p <project-id> --routes '[
  {"screenId": "abc", "route": "/"},
  {"screenId": "def", "route": "/about"},
  {"screenId": "ghi", "route": "/contact"}
]'

This generates a deployable Astro project with all screens mapped to routes.

File Structure

project/
  .stitch/
    metadata.json      # Stitch project & screen IDs
    SITE.md            # Site vision, sitemap, roadmap
    next-prompt.md     # Current task (the baton)
    designs/           # Staging area for Stitch output
      {page}.html
      {page}.png
  site/public/         # Production pages

Agentic Workflow & Vibe Coding

• Iterative Design: Do not expect pixel-perfect UI on the first generation. Draft a V1 screen, review the HTML/image output, isolate specific layout or styling issues, refine exactly ONE variable (e.g., color, padding, or prompt phrasing) at a time, and regenerate until it matches the design intent.
• Vibe Coding: Commit your working HTML/CSS states and next-prompt.md files locally before attempting risky redesigns or merging multiple generated screens into the main application.

DESIGN.md (Official Spec)

DESIGN.md is a dual-representation design system document following the google-labs-code/design.md specification. The file combines machine-readable design tokens (YAML front matter) with human-readable design rationale (markdown prose). Tokens give exact values. Prose tells why those values exist and how to apply them.

Creating a DESIGN.md

1. From concept -- Describe aesthetic intent; generate YAML tokens and markdown
2. From existing brand -- Provide URL or image; extract palette, typography
3. From existing project -- Use get_project + get_screen to synthesize

Feed content into the designMd field when calling create_design_system.

File Structure & Validation

A DESIGN.md file has two layers:

1. YAML front matter — Machine-readable design tokens, delimited by --- fences at the top. Supported token schemas: colors, typography, rounded, spacing, components.
2. Markdown body — Human-readable rationale organized into ## sections.

Validate a DESIGN.md file, catch broken token references, and check WCAG contrast ratios using the official CLI:

npx @google/design.md lint DESIGN.md

Official Format Example

---
name: Heritage
colors:
  primary: "#1A1C1E"
  secondary: "#6C7278"
  tertiary: "#B8422E"
  neutral: "#F7F5F2"
typography:
  h1:
    fontFamily: Public Sans
    fontSize: 3rem
  body-md:
    fontFamily: Public Sans
    fontSize: 1rem
  label-caps:
    fontFamily: Space Grotesk
    fontSize: 0.75rem
rounded:
  sm: 4px
  md: 8px
spacing:
  sm: 8px
  md: 16px
---

## Overview
Architectural Minimalism meets Journalistic Gravitas. The UI evokes a premium matte finish — a high-end broadsheet or contemporary gallery.

## Colors
The palette is rooted in high-contrast neutrals and a single accent color.
- **Primary (#1A1C1E):** Deep ink for headlines and core text.
- **Secondary (#6C7278):** Sophisticated slate for borders, captions, metadata.
- **Tertiary (#B8422E):** "Boston Clay" — the sole driver for interaction.
- **Neutral (#F7F5F2):** Warm limestone foundation, softer than pure white.

## Typography
Headlines use semi-bold weight. Body text at 14-16px regular.

## Elevation
No shadows. Depth via border contrast and surface color variation.

## Components
- **Buttons**: Rounded (8px), primary uses brand blue fill, secondary uses outline
- **Inputs**: 1px border, surface-variant background, 12px padding
- **Cards**: No elevation, 1px outline border, 12px corner radius

## Do's and Don'ts
- Do use primary color only for the single most important action per screen
- Don't mix rounded and sharp corners in the same view
- Do maintain WCAG AA contrast ratios (4.5:1 for normal text)
- Don't use more than two font weights on a single screen

Stitch auto-generates named colors from base values: surface, on-primary, error, outline, etc., following Material color role conventions.

Design Modes

Stitch is a suite of specialized design engines, not one model.

Tip: Run the same prompt in Thinking 3 Pro and 2.5 Pro to compare. Use Fast for exploration, 3 Pro for finals.

Style Word Bank (for Redesign mode)

Combine art-direction keywords from these categories:

Layout & Structure: Bento Grid, Editorial, Swiss Style, Split-Screen

Texture & Depth: Glassmorphism, Claymorphism, Skeuomorphic, Grainy/Noise

Atmosphere & Era: Brutalist, Cyberpunk, Y2K, Retro-Futurism

Color & Contrast: Duotone, Monochromatic, Pastel Goth, Dark Mode OLED

Official Prompting Best Practices

Starting a design:

• Begin with a broad concept OR specific core functionalities
• Use adjectives to set vibe: "vibrant and encouraging" vs "minimalist and focused"

Editing screens:

• Make one major change at a time
• Be specific: target the exact element, screen, and visual change
• Example: "Change primary CTA button on login to larger size using brand primary blue"

Theme control:

• Colors: specific hex ("change primary to forest green") or mood-based ("warm, inviting palette")
• Fonts/Borders: "playful sans-serif font", "fully rounded button corners"
• Images: be specific about location and content

Variations (distinct from editing):

• For "what if" exploration, not incremental refinement
• Make big swings -- combine theme + layout changes
• Can run variations on top of a variation
• Pick best base, lower to REFINE, merge elements from other options

Common Pitfalls

• Do not retry generation on timeout -- it may still succeed. Use get_screen to check.
• Do not use GEMINI_3_PRO -- deprecated. Use GEMINI_3_FLASH or GEMINI_3_1_PRO.
• Append =w{width} to screenshot URLs before downloading (or use get_screen_image virtual tool).
• Keep edits focused. One change per call produces better results.
• In the build loop, always update .stitch/next-prompt.md before completing.
• Do not recreate pages that already exist in the sitemap.
• If MCP tools are unavailable, use the CLI fallback: pnpx @_davideast/stitch-mcp tool <name> -d '{...}'
• To diagnose auth issues: STITCH_API_KEY=your-key pnpx @_davideast/stitch-mcp doctor STITCH_API_KEY=your-key pnpx @_davideast/stitch-mcp doctor t already exist in the sitemap.
• If MCP tools are unavailable, use the CLI fallback: pnpx @_davideast/stitch-mcp tool <name> -d '{...}'
• To diagnose auth issues: STITCH_API_KEY=your-key pnpx @_davideast/stitch-mcp doctor