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 full burden. 'Focus/activate' implies a UI interaction that changes application state, but it doesn't disclose behavioral traits like whether it requires specific permissions, what happens if the app isn't running, or if it's destructive (e.g., interrupting other processes). This leaves significant gaps for an agent.

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 extremely concise ('Focus/activate an application') with zero wasted words, making it front-loaded and efficient. Every word earns its place, though this brevity contributes to gaps in other dimensions.

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 complexity (a UI interaction with potential side effects), lack of annotations, and no output schema, the description is incomplete. It doesn't cover behavioral aspects, usage context, or return values, leaving the agent with insufficient information to use it reliably.

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?

Schema description coverage is 100%, with the schema fully documenting the 'app_name' parameter. The description adds no additional meaning beyond what the schema provides, such as format examples or edge cases. Baseline 3 is appropriate when the schema does the heavy lifting.

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 action ('Focus/activate') and resource ('an application'), making the purpose immediately understandable. However, it doesn't differentiate from sibling tools like 'window_list' or 'run_applescript' that might also interact with applications, so it doesn't reach the highest clarity level.

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. With siblings like 'window_list' (for listing windows), 'run_applescript' (for scripting), and 'keyboard_shortcut' (for keyboard-based activation), there's no indication of when window_focus is preferred or what prerequisites might exist.

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