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

The description discloses the fallback to the public item page when the API is bot-blocked, which is not captured in the readOnlyHint/openWorldHint annotations. It also lists the exact data fields returned, adding useful behavioral context. It does not overexplain, but the disclosed details meaningfully go beyond annotations.

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?

The description is two sentences, front-loaded with the verb and resource, and wastes no words. The first sentence covers the core function and outputs; the second adds a valuable behavioral edge case. Every sentence 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 no output schema, the description compensates by enumerating the returned fields (title, description, price, brand, size, condition, photos, seller). It also covers the fallback behavior, making the tool's behavior fully understood for a simple fetch operation. No significant gaps remain.

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 input schema already provides full descriptions for both parameters (itemId and country), so the description does not need to add parameter-level detail. The description's mention of 'numeric id' aligns with the schema, but it adds no new semantic value beyond what the schema already states. Baseline 3 is appropriate.

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 opens with the specific verb 'Fetches' and identifies the resource as 'one listing by numeric id', clearly distinguishing this from the sibling search tools that query multiple listings. It concisely enumerates the returned fields, leaving no ambiguity about the tool's function.

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 establishes clear usage context: use this when you have a numeric item id and need the full listing details. It does not explicitly name alternatives or exclusions (e.g., when to prefer search_items), but the purpose is specific enough that the intended use case is implied. A minor omission prevents a higher score.

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