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

With no annotations, the description carries full behavioral burden and excels: it discloses determinism, verification, exactness, guest rate limits, api_key budget impact, the returned provenance envelope, the payload schema the tool enforces, and the output schema. These details leave no surprises about 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 well-organized into short, information-dense sections. Each sentence adds value, and the embedded schemas are necessary for correctness and clearly labeled. There is no fluff or repetition.

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 tool with no annotations, this description is fully self-contained: it covers purpose, supported units, determinism, rate limits, api_key handling, response envelope, payload constraints, and output schema. The presence of both payload and output schemas makes the tool's contract complete for an agent.

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 only defines payload as a generic object with additionalProperties true, but the description compensates fully by providing a precise JSON Schema for payload (value, from, to, required, additionalProperties false). It also explains that providing a Guild api_key upgrades the budget, adding meaning to the api_key parameter. With 0% schema coverage, this is strong compensation.

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 'Deterministic unit conversion' and explicitly enumerates supported dimensions (length, mass, time, data, temperature) with examples, making the tool's function unambiguous. It clearly distinguishes itself from sibling tools by specifying the exact resource and scope.

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 clear usage context by stating 'Exact factors, no model arithmetic errors' and 'Deterministic, fixture-verified', which tells users to prefer this tool over model arithmetic for accurate conversions. It also explains rate-limit behavior and how to use a Guild api_key for a member budget, plus the strict payload schema requirement.

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