Library stats

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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds only the hint that output is a 'summary ... with reading stats', without saying what is aggregated, whether counts are lifetime or filtered, or whether the result is cheap to call repeatedly.

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. Nothing could be trimmed without losing information.

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 present, the description carries the burden of describing the return value, and 'summary ... with reading stats' is too vague to tell an agent what fields or metrics come back. Given the tool is a zero-param, low-risk read, this is adequate but leaves an information gap.

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?

The tool takes zero parameters, so the baseline of 4 applies. There is nothing in the schema for the description to clarify, and it correctly does not invent parameters.

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 clear verb (Get) and resource (summary of Apple Books library with reading stats). It is implicitly distinct from the many list/search siblings because it is the only aggregate/summary tool, but the description never explicitly contrasts itself with the per-book or per-collection listing tools.

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?

Usage is only implied: an agent can infer you call this for an overview rather than a filtered list, but no when-to-use or when-not-to-use condition is stated, and no alternative sibling is named (e.g. get_books_in_progress, get_finished_books).

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