pixel_copy_region

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

The description goes well beyond annotations by explaining mode behavior ('over' composites respecting transparency; 'replace' overwrites including alpha), clipping for out-of-bounds coordinates, return JSON structure, preview feature, and error format. Annotations indicate destructive and idempotent, which the description aligns with. No contradictions.

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 very concise, consisting of four sentences that front-load purpose and use cases, then detail mode behavior, clipping, return values, and error handling. Every sentence adds value without redundancy.

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 complex tool with modes, clipping, preview, and return values, the description covers all critical aspects. It lacks only a minor detail on the format of the rendered image when preview=true. No output schema exists, but the description compensates by detailing the JSON structure. Annotations provide additional safety context (destructive, idempotent).

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 input schema already provides descriptions for all parameters (e.g., 'Source region left edge X', 'Region width in pixels', etc.), so schema coverage is high. The description does not add new parameter-specific information beyond what the schema gives. Baseline 3 is appropriate.

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 'copy', the resource 'rectangular region', and scope 'from one canvas onto another (or within the same canvas)'. Use cases like moving limbs, stamping, compositing further clarify purpose and distinguish it from sibling tools like pixel_draw_pixels or pixel_transform_canvas.

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 lists specific use cases (moving limbs between frames, stamping repeated parts, compositing) which imply when to use the tool, but it does not explicitly mention when not to use it or compare with alternatives. No direct exclusions or alternative tool names are provided.

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