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

Annotations already mark the tool as read-only and idempotent, so safety is covered. The description adds valuable behavioral context by revealing the calculation method (cube-root scaling from 1-carat anchors) and the limitation that results are typical proportions rather than exact measurements. No contradiction with annotations.

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 compact and front-loaded, with the core purpose stated first. Every sentence contributes a distinct piece of information: supported shapes, calculation method, and reliability caveat, with no wasted words.

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?

For a simple deterministic calculator with two parameters and no output schema, the description is complete: it identifies inputs, supported values, the calculation approach, the output type (millimeter dimensions), and the caveat about verification. An agent has enough information to invoke it correctly.

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 fully documents both parameters, including the allowed shapes, case-insensitivity, and carat constraints. The description adds little beyond restating the supported shapes, so the baseline of 3 is appropriate given 100% schema coverage.

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 clearly states the tool's specific purpose: approximating face-up millimeter dimensions for a diamond by shape and carat weight. It also lists the four supported shapes, making its scope explicit and distinguishing it from sibling search, definition, and price 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: use this tool for approximate dimensions of typical proportions, not as a guarantee for a specific stone. It explicitly directs verification to the grading report, which effectively communicates when not to rely on the result. It doesn't name a specific sibling tool as an alternative, but the exclusion is clear.

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