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

Annotations already declare readOnlyHint=false, idempotentHint=true and destructiveHint=false, so safety and repeat-call behaviour are covered structurally. The description adds genuine context beyond them by stating the default-folder placement and the folderId override, but says nothing about duplicate handling, permission requirements, or failure modes.

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?

Two short sentences with no filler; the primary action and its default behaviour come first, and the parameter-sourcing hint follows. Every clause conveys information an agent needs to select and invoke the tool.

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 additive tool with no output schema and full annotation coverage, the description covers the essentials: what it writes, where it writes by default, and where the required ID comes from. Minor gaps are duplicate behaviour (partially covered by idempotentHint) and how to discover a folderId.

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 50%: catalogId is documented in the schema, while folderId carries no schema description. The description partially compensates by explaining that folderId overrides the default folder, which is the key semantic an agent needs, but it adds no guidance on obtaining a valid folderId (e.g., list_shelves or similar).

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 pairs a specific verb ("Saves") with a specific resource ("a book to the reader's wishlist"), which clearly separates it from sibling write tools like add_book_to_library and add_book_to_shelf. It stops short of naming those alternatives explicitly, so differentiation is implied by the resource noun 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?

The sentence "Use a catalogId from search_books" gives useful prerequisite/sourcing guidance and implies a search_books -> add_to_wishlist workflow. However, there is no when-not guidance and no explicit mention of add_book_to_library or add_book_to_shelf as alternative destinations, so the agent must infer the routing itself.

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