Get book cover image

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

With no annotations provided, the description carries the full burden. It explicitly discloses that the return is image bytes, not text, and that an error occurs if the book has no cover. These are key behavioral traits, though it omits other potential errors or response specifics.

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 three short sentences, each earning its place: the core action, size guidance, and error case. It is front-loaded and free of redundancy.

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 tool with two parameters and no output schema, the description conveys the return format (image bytes), the parameter usage, and a key error case. It does not mention default size or MIME type, but the schema covers the default, and the described behavior is sufficient for an agent.

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%, but the description adds meaning by clarifying 'thumbnail' as small and 'full' as full-size, which enriches the schema's terse 'Image size (default 'full')'. It also reinforces the bookId requirement by mentioning the no-cover error condition.

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 'Get a book's cover image bytes (returned as an image, not text)', using a specific verb and resource. It distinguishes from sibling tools like get_book by emphasizing the image-byte return format and the tool's dedicated function.

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 provides guidance on using the 'size' parameter (thumbnail vs full) and notes an error condition, but it does not explicitly compare this tool to alternatives like get_book or state when to prefer it. Usage context is implied rather than directly contrasted with siblings.

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