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

No annotations are provided, so the description carries the behavioral burden. It adds useful context: the tool checks Rakuten and Yahoo! Shopping daily, and treats same-diameter/same-model items as equivalent. However, it does not disclose return format, read-only status, or edge-case 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?

Three short sentences, each contributing useful information: the purpose, the data source, and parameter semantics. The main purpose is front-loaded and there is no redundant 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 a single-parameter lookup with no output schema, the description covers what the tool searches, how to supply the diameter, and how results should be compared. It does not describe the response shape, but the agent has enough information to invoke the tool 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 already 100% for 'dia', so the baseline is 3. The description adds concrete examples (67, 77, 52) and clarifies that dia is a numeric diameter, not a product code, which goes beyond the schema's 'フィルター径（mm）'.

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 tool returns 'レンズフィルターのきょうの最安値' and scopes it by filter diameter, specific filter types, and marketplaces. It is easy to tell apart from the lens_* siblings in general, though it does not explicitly name an alternative tool.

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 gives input guidance ('dia はフィルター径の数字') and a comparability note, but it does not state when to prefer this tool over sibling tools, nor when not to use it. No exclusions or alternatives are mentioned.

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