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

Beyond the readOnlyHint annotation, the description adds valuable behavioral context: 'The photo is never stored' and details the underlying process ('Uses Claude Vision... matches by CIEDE2000 perceptual distance'). This gives the agent a richer sense of side effects and mechanisms without contradicting the annotation.

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 moderately long but every sentence earns its place: action, outputs, method, privacy, and an example. It is front-loaded with the core purpose and structured logically. No fluff, though it could be slightly tighter.

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 exists, the description needn't detail return structure. It fully explains the analysis, the palette with provenance, the avoidance list, and privacy. Missing pieces like error conditions are minor and not required for selection. It is complete for an agent to decide when to invoke this tool.

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 coverage is 100%, so baseline is 3. The description adds semantic value by clarifying the mutual requirement: 'Either image_url or image_base64 required' — a constraint not captured in the schema's `required: []`. It also clarifies input type ('portrait photo') beyond individual parameter descriptions.

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 ('Upload a portrait photo and receive a full personal colour analysis') and clearly enumerates the outputs: seasonal type, depth, undertone, and a curated palette. It distinguishes itself from sibling palette tools by emphasizing personal portrait analysis and unique outputs like seasonal classification.

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 implies usage context (when you have a portrait photo and need personal colors) but never explicitly contrasts with sibling tools or states when not to use it. No alternatives are named, so while the context is clear, the guidance is implicit rather than explicit.

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