Mask a source to a shape

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

Annotations are sparse (readOnlyHint=false, destructiveHint=false). The description adds behavioral details beyond annotations, such as the default behavior for omitted format ('applies to both canvases') and clear semantics for 'None'. This enhances transparency.

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 two sentences, front-loaded with the core verb and resource, and every detail earns its place. It is concise yet packs meaningful information about shapes and defaults.

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 tool with 5 parameters and no output schema, the description is fairly complete: it explains the two most complex parameters (shape and format) and their defaults. However, it omits any mention of 'Squircle' and does not fully define 'format' beyond the default behavior, leaving minor 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?

Schema description coverage is only 20% (only radius has a description). The description compensates by explaining the meaning of shape enum values (Circle, RoundedRectangle, RoundedRectangle9x16, None) and the impact of omitting format. However, it does not clarify source_id or scene_id, but those are less ambiguous.

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's function with a specific verb ('mask') and resource ('source'), and elaborates on shape-specific behaviors (e.g., 'Circle inscribes a circle'). This distinguishes it from sibling tools like set_source_crop and set_source_transform.

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 provides practical usage context, such as 'great for round webcam cams' and notes that 'None clears the mask', but it does not explicitly mention alternatives or when not to use this tool. This is clear context without exclusions.

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