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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds meaningful behavioral context by disclosing a specific failure mode: 'Returns an honest `credentials_required` error until the upstream deployment has eBay app credentials provisioned.' This alerts the agent to potential auth-related failures and is beyond the structured 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 with no filler. The first sentence front-loads the purpose and key fields, the second adds a critical error behavior note. Every word 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?

For a simple single-item lookup with no output schema, the description adequately covers what the caller receives (the list of fields), how to identify the item (id or legacy_id), and a notable failure condition. No critical 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?

Schema description coverage is 100% (all three parameters have descriptions). The description's mention of 'REST item id or legacy numeric id' reinforces the relationship between `id` and `legacy_id`, but this is already conveyed in the schema (legacy_id says 'used when `id` is omitted'). No additional semantic value beyond the schema is provided.

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 uses a specific verb and resource: 'Get one eBay item's full detail' and enumerates the included fields (description, brand/MPN/GTIN, color, item specifics, images, return terms, availability, item end date). The 'one' and 'by REST item id or legacy numeric id' clearly distinguish it from the sibling get_ebay_items, which implies bulk retrieval.

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 clearly states the input mode ('by REST item id or legacy numeric id') and the singular scope ('one eBay item'), making the use case evident when a specific item ID is held. However, it does not explicitly mention alternatives like search_ebay or get_ebay_items for broader queries, nor does it state when not to use this tool.

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