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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds only that the listing is 'public' and results are 'normalized' – useful but thin. No mention of rate limits, auth, or error behavior when an item_id is invalid.

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, zero waste, and the purpose is front-loaded ahead of the parameter note and the sibling pointer. Nothing is padded.

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 full schema coverage, annotations covering the safety profile, and an output schema to describe returns, the definition is nearly complete. It could still note that item_ids come from ebay_search results, but the essentials are 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% and the schema already documents item_id with the identical example. The description repeats that same example inline, adding no syntax or format meaning beyond the structured field. Baseline 3 is correct.

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 and resource: 'Returns normalized details for a public eBay item listing.' An agent can distinguish this from ebay_search (search listings) and ebay_seller (seller info) because the description explicitly names the search sibling.

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: 'Use ebay_search to search eBay listings,' which frames this tool as the single-item lookup reached after a search. It doesn't state prerequisites like needing an item_id from search results, but the context is clear.

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