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

Annotations already declare readOnlyHint=true, so the safety profile is known. The description adds valuable behavioral context by detailing the return structure (verdict, risks, required actions, light behaviour under three illuminants, substrate notes, recommended alternative) and the method (CIEDE2000 archive matching, Claude material knowledge). This goes beyond the annotation baseline, though it does not mention limitations or edge cases, so a 4 is appropriate.

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 concise and front-loaded: it states the purpose in the first sentence, then enumerates return values, underlying method, and illustrative examples. Every sentence earns its place, and the structure is scannable. It is appropriately sized for the tool's complexity.

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 readOnly annotation, 100% schema coverage, and an output schema, the description is quite complete. It covers purpose, outputs, method, and use-case examples. It could additionally mention limitations or explicit alternatives, but overall it provides sufficient context for an agent to select and invoke the tool correctly.

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 100%, meaning all five parameters are already documented with descriptions in the schema. The tool description does not add specific parameter-level semantics beyond what the schema provides, though it does give examples of hex and substrate values. With full schema coverage, the baseline of 3 is appropriate.

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 opens with a specific verb+resource: 'Assess whether a hex colour can be safely specified for a physical application.' This clearly distinguishes it from sibling tools by emphasizing safety for physical applications, and the listed outputs (verdict, risks, actions, light behaviour, substrate notes) reinforce its unique purpose.

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 clear context for when to use the tool: when a physical application safety check is needed. It does not explicitly name alternatives or exclusions, but the purpose is sufficiently distinct from siblings like colour_compare or colour_metrics. Examples further illustrate appropriate use cases, earning a 4 rather than a 5.

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