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

Annotations already declare idempotentHint=true and destructiveHint=false, but the description makes that concrete: "Adding a book that is already there just returns it" tells the agent no duplicate is created and no error is raised. It also discloses the default status applied when the optional parameter is omitted, which annotations cannot express.

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?

Three short sentences with no filler: purpose and default first, the required-id source second, idempotency last. Everything is front-loaded and each sentence carries distinct information.

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 mutation with full schema coverage and no output schema, the description covers purpose, default behavior, and idempotency, which is what an agent needs to call it correctly. The only gap is that it never contrasts the tool with its shelf or wishlist siblings.

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% and both parameters are already documented, so the baseline is 3. The description adds one genuinely new fact, the TO_READ default for the optional status field, but says nothing further about the enum values or the catalogId pattern.

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 ("Adds a book to the reader's library") and the parenthetical scope note ("Want to read by default") separates it from shelf and wishlist variants. It does not explicitly name the siblings it replaces, so the differentiation is implied rather than stated.

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 one concrete usage prerequisite, "Use a catalogId from search_books", which routes the agent to the right source for the required argument. It never states when to choose add_book_to_shelf or add_to_wishlist instead, so the when-not guidance is left to inference.

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