Stitch MCP — Update Design System

Updates an existing Stitch Design System. Use this to modify theme properties, design tokens, or style guidelines without creating a new design system.

Critical prerequisite

Only use this skill when the user explicitly mentions "Stitch".

You must have the design system's asset name before calling this. If you don't have one:

• List existing design systems via stitch-mcp-list-design-systems
• Or use the name returned from stitch-mcp-create-design-system

When to use

• User wants to modify colors, fonts, or roundness of an existing design system
• After reviewing a design system and wanting to adjust specific properties
• Updating design tokens after a brand refresh

Call the MCP tool

{
  "name": "update_design_system",
  "arguments": {
    "name": "assets/15996705518239280238",
    "projectId": "3780309359108792857",
    "designSystem": {
      "displayName": "SaaS Dashboard Theme v2",
      "theme": {
        "colorMode": "DARK",
        "headlineFont": "GEIST",
        "bodyFont": "GEIST",
        "labelFont": "GEIST",
        "roundness": "ROUND_TWELVE",
        "customColor": "#818CF8"
      }
    }
  }
}

Parameter reference

Three sibling top-level arguments — name is not nested inside designSystem:

Argument	Type	Required	Description
name	string	Yes	Asset identifier with the assets/ prefix, e.g. assets/15996705518239280238. Top-level, not inside designSystem.
projectId	string	Yes	Bare numeric project id, no projects/ prefix
designSystem	object	Yes	{displayName, theme} — see below

designSystem — {displayName, theme} only

Field	Type	Required	Description
displayName	string	Yes	Human-readable name
theme	DesignTheme	Yes	Visual configuration (see stitch-mcp-create-design-system for the full field reference)

update_design_system takes the asset id prefixed (assets/159967...), while apply_design_system takes the same id bare. Two tools, same identifier, different formats.

designTokens and styleGuidelines are not accepted — the live API has no such fields on DesignSystem. Don't send them.

Note: This is a full replacement, not a merge. Include all theme fields you want to keep, not just the ones you're changing.

Output

Returns the updated Asset object:

{
  "name": "assets/15996705518239280238",
  "displayName": "SaaS Dashboard Theme v2",
  "designSystem": { ... }
}

After updating

• Offer: "Re-apply this updated design system to existing screens?" → stitch-mcp-apply-design-system
• Screens generated before the update won't automatically reflect changes — they need to be re-applied