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

Annotations already cover the safety profile (readOnly, idempotent, openWorld), and the description adds genuinely non-obvious behavior: 15-minute result caching, per-search request billing including cache hits, free failed searches, cursor-based paging, and the 100-row page cap.

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?

Four short sentences, each carrying distinct information (capability, pagination, caching, cost) with a doc link last. Front-loaded with the core capability and zero filler.

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 an 11-parameter read tool with no output schema and rich annotations, the description covers capability, cost, caching, and paging well. It could say slightly more about the returned shape (e.g. that results carry a next_cursor), but the cost/cache disclosure is the higher-value content and it is present.

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%, so the schema already documents all 11 parameters in detail. The description restates the 'up to 100 rows' cap and cursor paging but adds no syntax or semantic 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?

The first sentence names a specific verb (Search), resource (Mercari US active listings), scope (one page), and primary input (keyword), plus a row cap. 'Active' implicitly distinguishes it from the sibling mercari_sold, and 'Mercari' separates it from the other marketplace_* siblings.

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?

Usage is implied by 'search by keyword' and the cursor note tells the agent how to paginate, but there is no explicit when-to-use/when-not guidance and no mention of when to prefer mercari_sold or a different marketplace tool instead.

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