Current reading position

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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=false), yet the description adds real behavioral context: a platform/format limitation, and a fallback path that infers position from the most recent highlight and labels it as such. The only omitted details are error behavior for a missing/invalid book_id.

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?

Front-loaded with the core return value, then the follow-up action, then applicability limits, then the arg. Every sentence carries new information with no filler.

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?

With no output schema, the description appropriately describes the returned fields and the fallback labeling, so an agent knows what it will receive. Missing only failure-mode guidance (unknown book_id, DRM books) for full completeness.

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%, so the description carries the burden, and it does: 'book_id: The book's numeric ID' clarifies the expected type beyond the bare integer title. It adds little else (no ID discovery pointer), so it is helpful but not exhaustive.

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?

States a specific verb and resource ('Return where the user last left off reading a book') and enumerates exactly what comes back (chapter title and chapter_id, no text) plus an Open in Books link. Combined with the routing hint to get_chapter_content, an agent can distinguish this from sibling chapter/annotation tools without opening the 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?

The description gives an explicit chaining instruction ('Follow up with get_chapter_content for the text') and scopes applicability ('Works for non-DRM EPUBs downloaded to this Mac'). It stops short of naming sibling alternatives such as get_books_in_progress, but the use condition is unambiguous.

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