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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuine context by disclosing the return payload shape, notably that only 'a passage of its text' is returned rather than the whole book. It says nothing about behavior for an unknown id or whether the passage is truncated by size.

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 sentence that leads with the resource and then the returned fields, with no filler. The field enumeration is a laundry list but each item earns its place by telling the agent what to expect in the response.

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?

For a one-parameter read tool with no output schema, the description carries the return-value burden well by enumerating the fields. The remaining gap is failure behavior for a missing or ambiguous slug, which an agent would need to handle correctly.

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?

With one parameter at 100% schema description coverage, the schema already explains that 'book' accepts an id or slug as returned by search_books, list_books or get_author. The description contributes nothing beyond that, so the baseline 3 applies.

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 specific resource ('one book's details') and enumerates exactly what comes back, so the agent knows it is a single-record fetch rather than a list. The verb is implicit (the name and title carry 'get'), and no sibling is named, so it stops short of full differentiation from get_author or search_books.

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?

There is no statement of when to use this versus search_books or list_books, and no prerequisite such as obtaining the id from a prior search. Usage is only inferable from the fact that it returns one book's full detail, which is not explicit guidance.

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