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

Annotations already cover readOnly, idempotent, openWorld and destructive hints, and the description adds a genuinely useful operational fact: a flat 5-point cost per successful run. It also previews the payload (price, points, shipping, rating, SKU variants), though it doesn't note rate limits or error behavior.

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 leads with the action and identifier, then lists return fields and the cost. No filler, nothing repeated.

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 no output schema, the description compensates by naming the returned fields, and the annotations carry the safety profile. Combined with the cost note, an agent has everything needed to call it correctly.

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 item parameter, so the schema already documents the accepted formats and example. The description restates the shop_code/item_code vs URL duality without adding syntax beyond what the schema provides; 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 ("Get one Rakuten Ichiba item") and enumerates the returned fields, which clearly separates it from run_rakuten_items_search and run_rakuten_items_reviews. It never names those siblings explicitly, so it lands at 4 rather than 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 accepted input forms (shop_code/item_code or URL) are given, which implies this is the single-item lookup path, but there is no explicit when-to-use/when-not guidance or reference to the search or reviews siblings. Usage is inferred rather than stated.

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