Set Fill

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

Annotations provide idempotentHint and openWorldHint, and description adds useful behavioral details like image size limits, auto-resizing, and rejection criteria. It does not contradict 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 sentences, front-loaded with the core function, second sentence gives alternatives. No wasted words.

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?

Covers all use cases (color, image, clear), addresses constraints (image size, auto-resize), references sibling tools. Output schema exists so return values are not needed.

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 has 100% description coverage so baseline is 3. The description adds extra context for the 'clear' and 'image' parameters beyond schema descriptions, such as constraints on image dimensions and format.

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 sets a node's fill to an RGBA color, image, or clears it. It distinguishes from sibling tools by referencing `node_apply_style` and `node_bind_variable` for shared styles/tokens.

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?

Explicitly says when to use this tool vs alternatives: 'Use `node_apply_style` to link a shared paint style, or `node_bind_variable` to bind a color token.'

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