render_region

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

Annotations already declare readOnlyHint=false and destructiveHint=true, so the safety/mutation profile is carried by structured data. The description adds no further side-effect detail (e.g., file overwrite behavior), but it does not contradict 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.

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

The description is short and front-loads the core operation, followed by a useful workflow phrase. The English/Chinese duplication doubles length slightly, but it is still economical and not padded.

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 six-parameter tool with no required fields, the schema documents all parameters and the annotations cover side effects. The description supplies the intended workflow and rectangle semantics, making it sufficient; only explicit return/output details are absent, and no output schema exists to fill that gap.

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%, and the description only restates the rectangle parameters at a high level. It adds the 'pixel coordinates' framing and the lighting-check use case, but no parameter meaning beyond the schema, so the baseline of 3 applies.

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: 'Render only a rectangular region of the frame in pixel coordinates x,y,width,height.' The qualifier 'only' and the region focus clearly distinguish it from sibling render tools like render_still or render_frames that target the full frame.

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 gives a clear use case: the 'check the lighting on this one area' workflow. It does not name alternatives or state when not to use it, so it lacks explicit exclusion guidance, but the context is unmistakable.

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