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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds modest context: results are 'curated' recommendations delivered as 'normalized listing summaries', implying pre-shaped, pre-ranked output. It does not mention pagination or freshness, so this is adequate rather than rich.

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 zero waste, front-loading the tool's own purpose before the sibling-routing sentence. Every clause earns its place.

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 an output schema present, return values need no explanation, and with zero input parameters there are no inputs to document. The description fully covers what the agent needs to select and call this tool.

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 tool takes zero parameters, so the baseline of 4 applies. There is nothing for the description to compensate for, and it correctly describes a parameterless feed.

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 (Fetch) plus the exact resource (Mercari's curated home-feed recommendations) and pins the output shape ('normalized listing summaries'). It is clearly distinct from the search/autocomplete/detail siblings by virtue of being a parameterless curated feed.

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?

Explicitly routes the agent away from this tool for querying (mercari_search), typeahead (mercari_autocomplete), and item details (mercari_item, mercari_master). It does not spell out the positive condition ('use when you want general recommendations with no query'), but the alternatives and their domains are named clearly.

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