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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered without prose. The description adds genuine value with the '(cost: 1 credit)' disclosure, which is not available in any structured field. However, it omits behavior for the all-optional parameter set — what a call with no arguments returns is left undisclosed.

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?

A single front-loaded sentence plus a parenthetical cost note — nothing wasted and the two modes come first. It is arguably terse to the point of under-specification, but no sentence is filler.

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 simple three-parameter read tool with no output schema, the description covers the core modes and cost. It falls short on the ambiguous cases (no arguments, both arguments) and on what a search result set contains, which the missing output schema leaves entirely undocumented.

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%, so the baseline is 3, and the schema 'descriptions' are only type stubs ('string', 'number 1-25'). The description does add meaning by tying isbn to details and query to title/author search, but the limit parameter and its interaction with search results is never explained.

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 concrete resource (book details) and two distinct modes — ISBN lookup versus title/author search — which is more than a restatement of the name. It does not explicitly distinguish itself from lookups in adjacent domains (wikipedia_summary, wikidata_lookup, doi_lookup), but the resource is narrow enough that confusion is unlikely.

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 two modes imply when to use which parameter (isbn for details, query for search), but the mapping is only implied, not stated. There is no guidance on what happens if both or neither are supplied, and no mention of when a different tool would be preferable.

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