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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely new behavior: the optional expansion is capped at 10 books, ordered by most recent publication, and tags are either machine-generated or backed by at least three reader votes — details neither the annotations nor the schema disclose.

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?

Two sentences, front-loaded with the lookup action and id source before the optional expansion, with no filler. The second sentence's long enumeration of returned book fields partially duplicates the output schema, which keeps it from a 5.

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 two-parameter read tool with an output schema and full annotation coverage, everything an agent needs is present: id provenance, the optional expansion's cap and ordering, and tag provenance semantics. No material 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 coverage is 100%, so the baseline is 3, but the description earns more by specifying what include_books actually yields: up to 10 books, newest first, with named fields. That is more than the schema's bare 'Also return up to 10 of the author's books.'

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 opens with a specific verb and resource ('Look up an author in the ShelfClub catalog') and immediately pins the scope to a ShelfClub author id. It also distinguishes itself from the sibling get_book by explaining the provenance link ('which get_book returns for the authors of a book'), so an agent can route between the two without opening a schema.

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?

It gives clear context for when this tool applies and how to obtain the required id from a get_book result, which is the main workflow trigger. It stops short of stating when not to use it or naming an explicit alternative for author search, so it is strong but not fully explicit about alternatives.

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