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

Given readOnlyHint is already present, the description adds substantial behavioral context: each answer names its source, locator, and what the evidence CANNOT support; responses explicitly avoid averaging incompatible metric types; and output is evidence-led rather than a summary. This goes well beyond the annotation and materially helps an agent predict the tool's behavior.

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 dense but every sentence earns its place: core purpose first, then source list, then example questions, then the critical non-interchangeability caveat. The longer source enumeration is justified by the tool's broad historical scope. It remains well-structured and front-loaded.

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 tool is complex with five parameters and seven distinct source types, but the description covers the essential gaps: which sources exist, how to frame queries, what the response includes, and a key behavioral constraint. With rich schema and output schema already present, nothing critical is missing for an agent deciding whether and how to invoke it.

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?

The input schema already covers all five parameters with descriptions, so the baseline is 3. The description adds contextual color about the seven valid sources and the plain-English nature of queries, but it does not explain per-parameter formats or constraints beyond the schema. It is adequate but not necessary for parameter understanding.

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 action: 'Ask a question about how historical colour authorities actually reasoned, and get evidence with provenance rather than a summary.' It names the resource (seven historical sources) and the distinctive output type, which clearly separates it from colour/palette or archive siblings. The scope and intent are unmistakable.

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?

It provides concrete use cases: 'how do I paint a leaf', 'what did Bradley's disc proportions measure', and checking claims attributed to the named authors. It also warns that the source numbers are NOT interchangeable and that the tool will not average them. It does not explicitly name sibling alternatives or state when not to use this tool, so it falls just short of a 5.

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