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

Annotations already declare readOnlyHint, destructiveHint=false and openWorldHint, and the description adds genuinely new operational facts: pricing ($0.01/call via x402 USDC or card key, first 25 free, failed calls free) and that repeated calls are charged, which explains the idempotentHint=false. The sentence "Reads or computes only and changes nothing" largely restates readOnlyHint rather than adding nuance, and there is no mention of result pagination or total-hit behaviour.

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-loading is good — purpose and routing come before pricing — but the opening is a long run-on sentence that packs the field list, source, licence and filtering note together. The clause "Reads or computes only and changes nothing" duplicates the readOnlyHint annotation and could be cut without loss.

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 enumerates the returned fields, and the cost model is fully spelled out so the agent knows calls are metered. Minor gaps remain: no statement of what happens when no works match, and no hint on total availability versus the 20-item cap.

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 100%, so the schema already defines all four parameters and their bounds; the description's "up to 20 works" and "ISBNs (up to 5)" confirm the outputs rather than the inputs. It does add value beyond the schema by showing what q actually accepts (free-text words over title/author) through the worked example, which disambiguates q from the dedicated title/author params.

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 ("Search books by title, author or any words") and enumerates the returned fields plus the data source (Open Library catalogue, CC0). It separates itself from the neighbouring book_isbn/validate_isbn tools with "Use to find a book's ISBN, an author's works or editions before an ISBN lookup."

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?

Gives concrete when-to-use guidance (find an ISBN, enumerate an author's works or editions prior to an ISBN lookup) and clarifies a choice point with "Filter by author or title alone if you like." It also supplies a worked example, q=dune frank herbert, so the agent knows the expected query shape.

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