Selection

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

Discloses that the tool reads or changes the active selection and that the selection subsequently scopes drawing, transforms, and recoloring. This adds behavioral context beyond the annotations, which already flag readOnlyHint=false and idempotentHint=true. No contradiction with 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?

Two tight sentences front-load the purpose, list all operations, and provide a cost/benefit rationale. Every phrase earns its place with no filler or 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?

Given the output schema and annotations, the description sufficiently covers the conceptual model and op variety. Minor details like how mode combines with the existing selection or how rect coordinates are specified are left to the schema, which is acceptable for a tool with rich structured metadata.

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 descriptions already cover frame, layer, amount, sprite, color, and contiguous, and the enum values are self-explanatory. The description adds meaning only for the 'color' operation ('select every pixel matching a colour'). With schema coverage at 70%, the description provides modest additional value but does not compensate for undocumented params like rect and mode.

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?

States a specific verb and resource ('Read or change the active selection') and enumerates all nine operations. The selection resource is clearly distinct from sibling tools like layer, draw, transform, and recolor, so an agent can tell them apart without opening the schema.

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?

Explains that a selection scopes draw, transform, and recolor, and that it is usually cheaper and safer than masking by hand. This gives clear contextual guidance for when to use the tool, though it does not explicitly name sibling alternatives or state when not to use it.

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