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

Annotations already mark the tool as read-only, idempotent, and non-destructive. The description adds useful behavioral context beyond that: results are fetched live from Gutendex, ranked by relevance then popularity, and limited to ~78,500 public-domain books. It stops short of noting response shape details like pagination or empty-result behavior, but with the annotation safety profile, the added context is solid.

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 sentences with no filler: scope, search modes/filters, ranking, return fields, and the sibling alternative are all covered. Key differentiating information is front-loaded before the filter and return details.

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?

Given there is no output schema, the description compensates by stating exactly which fields each result contains. Combined with the schema's parameter documentation, the agent has everything needed to invoke the tool correctly: what to search, how to filter, how results are ordered, and when to switch to book_fulltext_search.

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 each parameter already includes a clear description with examples. The description adds only light semantic glue by grouping query as the keyword and author/subject/language as optional filters, but it does not materially extend what the schema already communicates.

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 names a specific verb ('Search'), a specific resource (the full Project Gutenberg catalog via Gutendex), and the supported access points (title/author/subject keyword, plus filters). It also differentiates itself from book_fulltext_search, so an agent can tell which search tool to use without inspecting schemas.

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 explicitly tells the agent when to use the alternative sibling: 'Use book_fulltext_search to search inside the locally indexed top books.' This creates a clear boundary between catalog-level metadata search and full-text content search, which is the main ambiguity a searcher could face.

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