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

The annotations already declare this as read-only, idempotent, and non-destructive. The description adds useful behavioral context beyond annotations by stating the access constraint ('no public directory') and what data the caller can expect. No contradictions with annotations exist.

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?

Two tight sentences with no filler. The core purpose and returned fields are front-loaded, and the access constraint is stated efficiently in the second sentence.

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 a rich output schema and clear annotations, the description is fully adequate. It specifies the input requirement, the data returned, and the key constraint, leaving nothing essential unexplained.

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%, with the parameter already documented as a marketplace listing UUID. The description reinforces that the UUID must be known in advance, but adds little new meaning beyond the schema for the single parameter.

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 operation ('Fetch a marketplace listing by id') and names the key returned fields: title, description, per-license pricing, terms, and sales totals. This makes the tool's purpose specific and distinguishable from sibling tools like list_my_listings or get_portfolio.

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 provides clear usage context by explaining that there is no public directory and the caller must know the listing UUID. This tells the agent when it can and cannot use the tool, though it does not explicitly name alternatives for discovering listings.

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