stitch-mcp-stdio

apply_design_system

Destructive

Update selected screens to match a design system by applying its colors, fonts, and shapes. Use when you need to restyle one or more screens for brand consistency.

Instructions

Applies a design system to a list of screens. Use this tool when the user wants to update one or more screens to match the style of a design system. This tool applies the selected design system's foundational design tokens (colors, fonts, shapes, etc.) to the chosen screens, modifying their appearance to align with the design system.

Input Schema

TableJSON Schema

Name	Required	Description
`assetId`	Yes	Required. The asset id of the design system to apply, can be fetched from 'list_design_systems'. Example: '15996705518239280238', without the `assets/` prefix.
`projectId`	Yes	Required. The project ID of screen instances to edit, example: '4044680601076201931', without the `projects/` prefix.
`selectedScreenInstances`	Yes	Required. The screen instances to edit, which is available in the Project info, fetched by `get_project`.

Output Schema

TableJSON Schema

Name	Required	Description
`projectId`	No	The project ID of the generated screen. This is the same as the input project ID.
`sessionId`	No	The session ID of the generated screen.
`outputComponents`	No	The generated output components.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Sep 20, 2026

TDQS

A4.1/5.0

Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already mark this as destructive and non-read-only. The description adds context by explaining the tool modifies screen appearance via design tokens, but it does not disclose potential overwriting or irreversibility of existing screen styles. It adds some behavioral value without contradicting the annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two sentences, front-loaded with the core action and usage guidance. Every sentence earns its place with no redundancy or filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool's purpose, usage trigger, and expected effect are clearly stated. The input schema fully documents all parameters and even explains where to find screen instances, and annotations cover safety traits. An agent has enough information to select and invoke the tool correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so all three parameters are already documented in the schema. The description adds minimal parameter-level meaning beyond naming colors, fonts, and shapes as applied design tokens, which does not need to compensate for any schema gap.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb and resource: 'Applies a design system to a list of screens.' It clearly describes the effect (applying foundational design tokens to modify appearance), which distinguishes it from sibling tools like create_design_system or update_design_system. The purpose is unmistakable.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly states when to use the tool: 'Use this tool when the user wants to update one or more screens to match the style of a design system.' It provides clear context, though it does not explicitly name alternatives or state when not to use it.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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