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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered structurally. The description adds useful context that this is public data sourced from Costco's own backend, but does not cover caching, rate limits, or freshness beyond that. With annotations carrying the safety burden, a 3 is appropriate.

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?

Front-loaded with the return payload, followed by data provenance and the id explanation. It is appropriately sized, though the escaped '\' artifact at the end of the id sentence is a minor structural blemish.

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 read-only lookup with an output schema present, the description says what is returned, where the data comes from, what the id is, and which sibling handles discovery. Return values need not be explained given the output schema, so the remaining gaps are minimal.

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% and the description's 'id' sentence is essentially a duplicate of the schema's own description. It reinforces where ids come from (search result's id field or a product page URL), but adds little beyond the schema, so 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 ('Returns') and resource ('a Costco product's detail') and enumerates the returned fields (title, description, manufacturer, image, price, stock status, rating). It clearly distinguishes itself from close siblings like costco_product_availability and costco_product_reviews, and explicitly routes lookups to costco_search.

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?

It names the alternative ('Use costco_search to search Costco products') and implies the correct precondition (this tool takes an id, so product discovery goes to search first). It lacks an explicit when-not clause, but the routing to the search sibling gives clear context for selection.

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