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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely useful non-schema behavior: the endpoint is an external (Open Library) source and it costs $0.002 USDC per call via x402, which is important for an agent budgeting calls. It omits pagination/limit behavior and error semantics, so not a 5.

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?

One compact sentence names the capability, source, and returned fields, with the pricing constraint appended cleanly. No filler, and the most decision-relevant information is front-loaded.

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 usefully enumerates return fields, and it discloses cost. However, for a 3-parameter tool with zero schema coverage and no output schema, it leaves pagination, parameter interaction (q vs isbn), and result-shape limits unspecified.

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 full burden. It hints that 'isbn' is an ISBN and that search is by book/title/author, but says nothing about 'limit' or about the relationship between q and isbn. The field list describes outputs, not input semantics.

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+resource combo ('Book search and ISBN lookup') and names the data source (Open Library), plus enumerates the fields returned. An agent immediately knows what it gets. It does not explicitly differentiate from potentially overlapping siblings like papers, libdocs, or research, which keeps it short of a 5.

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?

Naming two modes ('search' and 'ISBN lookup') implies that one uses a query and the other an ISBN, but there is no explicit when-to-use, no statement about whether the two can be combined, and no routing to alternatives. Usage is only implied.

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