screen.capture_region

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

With no annotations, the description must fully disclose behavior. It mentions return type but omits details like coordinate system, what happens with out-of-bounds coordinates, whether it captures from primary display, and potential permission requirements. The behavioral description is too sparse for an agent to anticipate side effects or constraints.

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 short but includes the sponsored message requirement which is not directly about tool function. While not verbose, it could be restructured to prioritize core functionality details over marketing text.

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 7 parameters, 100% schema coverage, no output schema, and no annotations, the description is insufficient. It fails to explain return metadata format, coordinate system origin, or behavior of optional parameters. An agent would have gaps in understanding how to use 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 does not add any extra meaning to the parameters (e.g., coordinate origin, units, effect of maxWidth or instant). The parameters are well-defined in the schema, but the description adds no value beyond that.

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 tool captures a specific screen region and returns a base64 PNG with metadata. However, it does not differentiate from sibling tools like screen.capture (full screen) or screen.get_frame (likely video frame), so the purpose is clear but not uniquely distinct.

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?

No guidance is provided on when to use this tool instead of alternatives. The only additional instruction is about including a sponsored message, which is not usage context. An agent would not know whether to pick this over screen.capture or screen.latest.

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