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

Annotations already cover read-only, idempotent and closed-world safety, so the bar is lower. The description adds meaningful behavior beyond them: the response is free, it is a real sample, and it is tied to a fixed example rather than a caller-supplied query. It does not describe the sample's shape or any rate limits.

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?

A single sentence, front-loaded with the most decision-relevant token ('FREE.'), with no repetition or filler. Every clause adds information about cost, return content, or scope.

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 one-parameter read-only tool with no output schema, the description covers what is returned, that it is free, and that the example is fixed. The remaining gap is route semantics: it does not clarify how the check/report/best samples differ, which matters for selecting the right enum value.

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 0%, so the description must carry the parameter meaning. It names the enum values in prose ('check, report or best') and frames them as paid response types, which helps, but it does not explain what distinguishes a check from a report or a best, leaving the agent to infer the route choice.

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?

States a specific verb ('Returns') and resource ('a real sample of a paid response'), and names the sibling product lines (check, report or best) it previews. The phrase 'for a fixed example' pins the scope so an agent can distinguish it from the real check/report/best tools without opening the schema.

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 purpose 'so you can see exactly what you would buy' makes the preview-before-purchase use case clear, and 'FREE' signals when cost matters. It does not explicitly say when not to use it (e.g., 'use check/report/best for actual queries'), which keeps it from a 5.

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