list_book_thumbnails

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

Annotations already declare readOnlyHint=true, and the description adds context beyond that by specifying that no image bytes are downloaded, clarifying the exact scope of the read operation. This is a useful behavioral disclosure that prevents expectations of binary content.

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?

The description is two concise phrases, front-loaded with the primary action and scope, and the negative clause adds value without redundancy. Every word earns its place.

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 simple read-only tool with a single parameter and an output schema, the description is complete: it names the resource, scope, and the critical behavior of not downloading bytes. The presence of an output schema means return structure does not need to be described here.

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 0%, and the description does not elaborate on the book_id parameter. The phrase 'for a book' hints that book_id identifies a book, but no format or additional semantics are provided. With only one simple parameter, the gap is minor, but the description does not fully compensate for the missing schema description.

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 clearly states the action ('List') and resource ('thumbnail metadata for a book'), and adds a key differentiator ('does not download image bytes') that distinguishes it from tools that retrieve images. This is specific and unambiguous.

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?

The description implies the tool is for metadata-only use cases by explicitly excluding image downloads, which gives the agent a clear sense of when to select it over potentially confusing alternatives like get_book_pages. However, it does not explicitly name alternative tools or state 'use this when...'.

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