macOS GUI Control MCP

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states what the tool does but lacks critical behavioral details: it doesn't specify the coordinate system (e.g., screen-relative, window-relative), color format (e.g., RGB, HEX), or potential limitations (e.g., permissions needed, performance impact). For a tool with zero annotation coverage, this leaves significant gaps in understanding its operation.

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

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

The description is a single, clear sentence with no wasted words. It's front-loaded with the core action ('Get pixel color') and specifies the target ('at coordinates'), making it easy to parse quickly. Every word earns its place by directly contributing to understanding the tool's purpose.

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

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

Given the tool's moderate complexity (screen interaction with coordinates), lack of annotations, and no output schema, the description is incomplete. It doesn't cover the return value (e.g., color data format), error conditions, or practical constraints. For a tool that interacts with system-level resources, more context is needed to use it effectively and safely.

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

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

The description mentions 'coordinates' which implies the x and y parameters, but with 0% schema description coverage, it doesn't add meaningful semantics beyond what the schema already shows. It doesn't explain what x and y represent (e.g., pixel positions, units), valid ranges, or coordinate origin. The baseline is 3 because the schema covers the parameters structurally, but the description fails to compensate for the lack of semantic detail.

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

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

The description clearly states the verb 'Get' and the resource 'pixel color at coordinates', making the purpose immediately understandable. It distinguishes itself from sibling tools like screen_capture and screen_get_size by focusing on color retrieval rather than capture or dimension measurement. However, it doesn't explicitly differentiate from all siblings, keeping it from a perfect score.

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

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

The description provides no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites (e.g., screen access permissions), typical use cases (e.g., UI testing, color sampling), or when other tools like screen_capture might be more appropriate. Without any usage context, the agent must infer when this tool is suitable.

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