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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered; the description's real contribution is the cost disclosure ('Costs 1 credit') and the note that reviews are only an 'inline sample'. It says nothing about failure modes for invalid IDs, marketplace/redirect behavior, or latency/rate limits, which would matter for a credit-metered call.

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, front-loaded with what the tool returns, then cost, then input rule. No filler or restatement of the title.

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 does the right thing by listing returned fields and flagging that reviews are partial. But for a 5-parameter, credit-costing tool it leaves the identifier-selection fallback, the three secondary parameters, and error behavior undocumented.

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 60%. The description's 'either product_id or url' is genuine added value because the schema marks neither as required and never states the alternatives are interchangeable. However, tld, country_code and cache_max_age receive no mention anywhere in the description, leaving a real gap.

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+resource ('Public details for an eBay listing') and enumerates the payload (title, price, condition, seller, sample reviews), so an agent knows exactly what it retrieves. It does not name ebay_search or explain why a single-listing lookup differs from a search result, so sibling differentiation is left implicit.

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?

'Pass either `product_id` or `url`' gives the minimum routing rule for inputs, which is more than nothing. But there is no guidance on when to use this instead of ebay_search, no preconditions, and no statement about what happens when neither identifier is supplied (schema marks zero required params).

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