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

Annotations declare readOnlyHint, idempotentHint, and destructiveHint false, which already convey the safety profile. The description adds the behavioral detail that it corrects for specific gravity, a meaningful calculation behavior. However, it does not mention other behavioral traits like output format or error handling, which are partially covered by the output 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 a single sentence with a clear main clause and a list of shapes. It is front-loaded with the purpose and the correction factor. It's concise enough, though it could be slightly trimmed, but it's well-structured and informative.

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 that an output schema exists, the description doesn't need to explain return values. It covers the key parameters (carat, shape, species) and the distinguishing feature (SG correction). It is clear enough for an agent to call the tool correctly. It doesn't mention edge cases, but they aren't critical for a simple estimation 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?

The schema describes shape and species with default values, but the description lists the allowed shapes explicitly (round, oval, cushion, etc.) and gives examples for species (sapphire, diamond, spinel, emerald, opal), adding clarity beyond the schema. The carat parameter is self-explanatory. With 67% schema coverage, the description adds value by enumerating options.

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 uses a specific verb 'Approximate' and a clear resource 'face-up millimetre dimensions'. It also distinguishes from 'diamond-only calculators' by correcting for specific gravity, making it clear what this tool does that others don't. This is a specific and unambiguous 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 implies when to use this tool: whenever you need face-up size for any gem species, unlike diamond-only calculators. It explicitly mentions the alternative (diamond-only calculators) and why this one is different, providing clear context. However, it does not explicitly state exclusions or when not to use it beyond the contrast.

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