Zoom into region

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

Annotations already declare readOnly, idempotent, and non-destructive behavior, so the description does not need to repeat that. It adds useful behavioral context: the coordinate space is the same as click, and the result text explains how to map pixels back to screen coordinates. This goes beyond the annotations without contradicting them.

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?

Three tight sentences: purpose/use cases, input format plus result behavior, and alternative routing. There is no filler or repetition; every sentence earns its place.

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?

For a read-only capture tool with fully documented parameters, the description covers why to use it, when to avoid it, how to specify input, and what the result will indicate. No output schema exists, but the description does disclose the essential result behavior, so the agent has what it needs to call the tool correctly.

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 coverage is 100%, so the baseline is 3; the description adds meaningful extra context by clarifying that the region is defined by two corners in the same coordinate space that click uses. It also explains why that matters by mentioning pixel-to-screen mapping in the result.

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 states a specific verb and resource: 'Capture one region of the screen at full resolution.' It also names concrete use cases (small text, dense tables, file names, tiny controls) and is clearly differentiated from the sibling screenshot tool by emphasizing regions at full resolution.

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?

It explicitly tells the agent when to use this tool versus alternatives: 'Use screenshot for a whole window and get_app_state when the text is exposed by accessibility.' This gives direct routing guidance beyond mere inference.

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