Apple Books "Customers Also Bought" recommendations.
| Name | Required | Description | Default |
|---|---|---|---|
| ID | Yes | Apple Books numeric book ID (required), e.g. 1037193578. | |
| Lang | Yes | Optional language code, e.g. en-US. | |
| Country | Yes | ISO-2 storefront country code, e.g. US. Default US. |
| Name | Required | Description | Default |
|---|---|---|---|
| data | Yes | The tool result payload (shape varies per tool; see each tool's docs resource). |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds nothing behavioral — not whether results are limited in count, whether they vary by storefront/language, or what the recommendations are derived from. It essentially restates the tool's marketing label.
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?
A single front-loaded sentence with no filler or redundancy. It is efficient, though the brevity is closer to under-specification than elegance.
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 need not be explained. What is missing is the minimal disambiguation an agent needs in a catalog this large: that this consumes a *book* ID (not an audiobook ID) and that it is the book-side counterpart to apple_books_audiobook_similar.
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 ID, Country, and Lang with examples and defaults. The description contributes nothing about parameter behavior, which is the correct baseline of 3 when the schema carries the full load.
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 names the resource (Apple Books recommendations) and the underlying data source ('Customers Also Bought'), so the intent is inferable. However it never states the operative verb — that these are *similar* books for a given book ID — nor differentiates itself from the sibling apple_books_audiobook_similar, which is nearly identical in name.
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?
No guidance on when to use this over apple_books_book, apple_books_book_reviews, or the audiobook variant. There is also no note that a book ID must first be obtained, even though all three parameters are required.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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