pixel_draw_ellipse

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

Annotations already indicate destructive and idempotent behavior. The description adds that drawing 'transparent' erases, describes the return JSON structure, and notes error format. This goes beyond annotations to inform the agent about side effects and output.

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 four sentences, front-loaded with the main action, and covers key usage details without redundancy. Every sentence adds value, making it efficient for an agent to parse.

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 there is no output schema, the description adequately explains the return value (JSON fields) and failure case. It covers all important aspects of a simple drawing tool, leaving no major gaps.

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?

Although the input schema provides descriptions for all parameters, the tool description adds conceptual context: the bounding box meaning, the relationship between width/height and circles, and the preview toggle. This aids understanding beyond the schema's individual field descriptions.

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 draws 'a filled or outlined ellipse inside a bounding box on a canvas', with specific detail on how equal width/height yields a circle. This distinguishes it from siblings like pixel_draw_rect and pixel_draw_line, which draw different shapes.

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 explains the bounding box coordinate system, the effect of 'transparent' color, and the preview option. While it doesn't explicitly contrast with siblings, the context is sufficient for an agent to understand when this tool is appropriate.

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