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

Even with readOnlyHint=true covering the non-destructive nature, the description adds substantial behavior: it discloses the transcription provenance caveat (member_source_caveat), the modern matching convention for label_placement_basis, tied-match disclosure via hex_collision, and the explicit null behavior instead of forced matches. These are exactly the kind of semantic and honesty-related behaviors an agent cannot infer from annotations or schema.

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 long, but each clause earns its place given the tool's provenance, matching, nulling, and caveat requirements. It is front-loaded with the core operation and source before moving into caveats. A small amount of redundancy ('silence is the honest answer' restates the null behavior) keeps it from a perfect conciseness score.

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 tool's source artefacts, algorithm, output shape (including archive_match and hex_collision), null semantics, transparency caveats, and differentiation from contrast tools. With full parameter coverage, an output schema, and a readOnly annotation, nothing necessary for correct invocation or interpretation is missing. The only minor gap is not naming additional sibling alternatives, but that is not required for completeness.

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% and the schema already explains hex and n_per_member, including the default's effect on the return shape. The description adds value by explaining how hex is interpreted: it is snapped to one of eleven hue-family labels, resolved against an archive, and nulled for near-neutral inputs. It does not duplicate the schema's parameter docs, but enriches the semantic context.

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 precise verb-resource pair: it 'returns every documented dyad or triad' from Vanderpoel's plates for a hue label derived from an input hex. It further distinguishes itself from hay_contrast by stating it carries no proportional ratio, isolating its categorical editorial purpose. This is enough for an agent to select it over sibling harmony and contrast tools.

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 gives clear context for when the tool should and should not produce results: it returns null for near-neutral inputs, undefined hue, or unrepresented labels, and explicitly contrasts itself with hay_contrast on the absence of proportional ratios. It does not, however, provide an explicit use-this-when statement or enumerate alternatives beyond that single contrast tool, so it falls just short of full routing guidance.

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