fill_rect

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

With no annotations, the description carries the behavioral disclosure burden. It does reveal a side effect ('refresh body-under ref') and a clipping/boundary behavior ('Overhang past body OK'), but it does not state whether existing pixels are overwritten, whether the operation is reversible, or what coordinate system x/y use.

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?

Three short, information-dense lines: the core action and side effect, the color format, and the usage preference. No filler or repetition.

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?

The description covers the core purpose, target layer, color, and preferred use case, which makes the tool callable. However, with 10 parameters and no annotations, important details like scale's effect, coordinate origin, and output handling remain implicit. The output schema covers return values, so omitting them is acceptable.

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 0% across 10 parameters. The description usefully clarifies color syntax ('hex / [r,g,b,a] / transparent') and the slot path, but leaves scale, plan_id, output_dir, and coordinate semantics undocumented.

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 names a specific operation and resource: 'Fill a rectangle on design/layers/<slot>.png', and adds the side effect 'refresh body-under ref.' It clearly distinguishes itself from ellipse/stroke/flood-fill siblings by specifying the shape and target.

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?

'Prefer this or paint_from_commands for blocky pixel-art clothing shapes' provides explicit when-to-use guidance and names an alternative. It also adds boundary context with 'Overhang past body OK,' though it doesn't state when to prefer stroke_rect or fill_ellipse instead.

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