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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety and live-source profile is covered. The description adds that results are 'normalized listing summaries' with a total matching count from a live marketplace, which is useful context, but no pagination, rate-limit, or result-count behavior is disclosed.

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 front-loaded sentence with no wasted words; the resource and return shape are stated immediately. Efficient, though it packs two clauses that could be split for readability.

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?

With a single documented parameter, an output schema, and annotations covering the safety profile, the description supplies everything an agent needs to call the tool correctly. Nothing material is missing for a one-param search.

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 coverage is 100% for the single 'query' parameter, which is already documented as free-text keyword search. The description adds no query syntax, filtering, or format detail beyond the schema, so the baseline 3 applies.

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+resource ('Mercari listing search') and describes the returned shape (title, price, thumbnail, condition, seller, plus total count), which clearly distinguishes it from mercari_item (detail) and mercari_autocomplete (suggestions). It does not explicitly name those siblings, so it stops short of a 5.

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 usage (it is the keyword search entry point for Mercari) but gives no explicit when-to-use, when-not, or alternative routing (e.g. use mercari_autocomplete to resolve a query, mercari_item for a specific listing). Adequate for a self-evident search tool, but no guidance is provided.

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