List chapters

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It explicitly states that it 'parses and caches the EPUB on first call,' discloses the EPUB-only format restriction, and clarifies that no text is returned. These are valuable behavioral traits beyond what the input schema or title convey.

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 sentences, each earning its place: the core purpose, the caching behavior, and usage guidance with an alternative tool. It is front-loaded with the key action and avoids redundant or filler language.

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?

The tool has a single parameter and no output schema, so the description must convey the return content. It does so by specifying 'sizes (character and word counts)' and 'chapters/sections.' It also covers operational details (parsing/caching) and usage context (pick a chapter for get_chapter), making it complete for this simple tool.

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 input schema has 100% coverage, as the only parameter bookId is described as 'The book's id (from search_books).' The description doesn't add parameter-specific details beyond that, but it does connect the parameter to the book context. Given the strong schema coverage, a baseline of 3 is appropriate.

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: 'List a book's chapters/sections with their sizes (character and word counts) but NO text.' This clearly states what the tool does and differentiates it from get_chapter, which presumably returns the chapter text. The EPUB-only note adds further clarity.

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 explicitly says 'Use this to see the book's structure and pick which chapter to read with get_chapter,' providing direct guidance on when to use this tool versus the sibling tool get_chapter. It also implies when not to use it (for reading text) by stating 'NO text' and 'EPUB only.'

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