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

Annotations only supply readOnlyHint=true, so the description carries some burden for behavioral disclosure. It adds context that this is a 'single-call' consolidating tool, and details what data is returned, which goes beyond the annotation. It does not mention potential error cases or performance characteristics, but given the read-only hint, the added return-context is valuable and non-contradictory.

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 well-structured and front-loaded with the primary purpose ('Canonical single-call colour truth object'). Every sentence carries useful information: return content, usage guidance, alternatives, and concrete examples. The examples add value, though they could be considered slightly verbose for a tool description.

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 tool's complexity (5 parameters, rich output schema, many sibling tools), the description is quite complete: it states what data is returned, when to use it, how it relates to alternatives, and provides examples. It does not discuss output schema specifics, but the presence of an output schema reduces that burden. Missing a 'when not to use' or edge-case note, but overall it's sufficiently contextualized.

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%, so the description need not explain parameters. It adds minimal parameter meaning beyond schema, only implicitly referencing hex values via examples. The description does not elaborate on n_archive or include_physics semantics, but the schema already covers these, so a baseline 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 states a specific verb and resource: 'Canonical single-call colour truth object. Returns everything known about a hex value'. It clearly enumerates the data categories returned and distinguishes itself from siblings by explicitly naming the tools it replaces ('Replaces chaining colour_dna + archive_provenance + colour_cultural_risk + colour_metrics separately').

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 explicit usage context: 'Use this as the foundation call when you need the complete picture.' It also names the alternative tools it consolidates, which implies when to use those instead (for specific sub-queries). However, it lacks explicit 'when not to use' exclusions or conditional guidance for different scenarios.

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