Stitch MCP — Create Design System from DESIGN.md

Turns an uploaded DESIGN.md into a real Stitch Design System and displays it in the UI. This is step two of a pair — stitch-mcp-upload-design-md must have run first, because this tool consumes the screen instance that upload created.

Calling it without a prior upload fails: there's no screen instance to point at.

Critical prerequisite

Only use this skill when the user explicitly mentions "Stitch" in their request. Never trigger Stitch operations silently during regular conversation.

When to use

• Immediately after stitch-mcp-upload-design-md returns — always, as a pair
• Never on its own

Step 1: Confirm you have the screen instance

You need two values from the upload step. If you didn't capture them, fetch them now with get_project (note: this one takes the projects/ prefix):

{
  "name": "get_project",
  "arguments": { "name": "projects/3780309359108792857" }
}

Take the newest entry in screenInstances and read off both id and sourceScreen.

Step 2: Call the MCP tool

{
  "name": "create_design_system_from_design_md",
  "arguments": {
    "projectId": "3780309359108792857",
    "selectedScreenInstance": {
      "id": "a1b2c3d4e5f6",
      "sourceScreen": "projects/3780309359108792857/screens/98b50e2ddc9943efb387052637738f61"
    },
    "deviceType": "DESKTOP"
  }
}

Three different ID formats in one call. This is the single easiest place to get it wrong:

Field	Format	Example
projectId	numeric only, no prefix	3780309359108792857
selectedScreenInstance.id	screen instance id — not the source screen id	a1b2c3d4e5f6
selectedScreenInstance.sourceScreen	full resource path, both prefixes	projects/.../screens/...

deviceType is optional: MOBILE, DESKTOP, TABLET, or AGNOSTIC. Omit it and Stitch decides.

Step 3: Confirm and capture the asset id

On success you get back a design system with an asset id in assets/NUMERIC_ID form. Store both forms: apply_design_system wants the bare numeric part, generate_screen_from_text's designSystem param wants the full assets/NUMERIC_ID string.

Announce it:

"Design system created from your DESIGN.md (asset 15996705518239280238). Want me to apply it to existing screens, or use it for the next generation?"

Step 4: Put it to work

• Apply to existing screens → stitch-mcp-apply-design-system
• Use for new screens → pass designSystem: "assets/15996705518239280238" to generate_screen_from_text

ID format rules (critical — different tools need different formats)

Tool	ID format required
create_design_system_from_design_md	Numeric projectId + the screen-instance pair above
upload_design_md	Numeric only: 3780309359108792857
apply_design_system	Numeric assetId, no assets/ prefix
generate_screen_from_text	designSystem does take the assets/ prefix
get_project	Full path: projects/3780309359108792857

Yes — apply_design_system wants the bare asset id while generate_screen_from_text wants it prefixed. Same identifier, two formats, depending on which tool you hand it to.

Integration

• Preceded by stitch-mcp-upload-design-md, always
• Followed by stitch-mcp-apply-design-system or a generation call
• List what already exists with stitch-mcp-list-design-systems