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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety and open-world profile is covered. The description adds that results come from the 'public catalog page' and include audiobooks 'where available', which is modest extra context. It reveals little else about behavior beyond what annotations provide.

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-loads the purpose, then gives inline parameter hints, then the alternative routing. Every sentence carries weight and there is no padding, though the parenthetical '(and audiobook, where available)' slightly interrupts the main clause.

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?

An output schema exists, so return values needn't be explained, and annotations cover the read-only safety profile. The description supplies purpose, parameter guidance, and one alternative, leaving it largely complete for a simple 3-param read tool. Only the when-to-use-vs-other-audiobook/author tools gap remains.

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%, so the schema already documents all three parameters. The description restates ID (numeric, required, example), Country (ISO-2, default US), and implies Lang, adding no syntax or meaning beyond the schema. Baseline 3 is appropriate when the schema does the heavy lifting.

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 author metadata plus full ebook/audiobook bibliography from Apple Books. This distinguishes it from apple_books_book and apple_books_audiobook, though it doesn't explicitly contrast against the other author-adjacent siblings. Clear and specific, marred only by incomplete sibling differentiation.

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?

Ends with an explicit routing statement: 'Use apple_books_book to retrieve Apple Books book details', naming an alternative and the condition that selects it. This gives clear usage context, but it only covers one alternative and does not state when-not to use this tool outright.

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