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

Annotations already declare read-only/idempotent/open-world, and the description goes well beyond them: it discloses that sellers publish no stock or prices, flags the `sponsored` field, explains `kind` values, and advises calling a shop with the ISBN. This is exactly the kind of caveat an agent needs.

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 core action, then dense with return-shape and caveat detail. The long retailer list is verbose but conveys real informational content; nothing is filler.

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 still fully explains the return structure (edition fields, online links with kind/sponsored, inStore with address/phone/hours/distance). An agent can invoke and interpret the result without guessing.

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%, so the baseline is 3; the description adds value by tying title to author, clarifying that item is a books-collection id, and restricting zip to US in-store lookups. It complements rather than repeats the schema.

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 resource (book) and outcome (where to buy it), and the description enumerates the exact answer shape (edition + online sellers + in-store). No book-related sibling exists to differentiate from, so the ceiling is a clear but non-differentiating purpose.

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 explains the three valid input modes (isbn, title+author, item) and the condition that unlocks in-store results (a US zip). It doesn't name exclusions or fallback alternatives, but the usage context is clear for each parameter.

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