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

Annotations already establish read-only, idempotent, non-destructive behavior, so the description doesn't need to repeat that. It does add genuinely new context: this reads the live catalog rather than the search index and is therefore never a snapshot, which tells the agent results may differ from a prior search.

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, front-loaded with the action and return contents, followed by freshness and then usage. No filler or restatement of the tool name.

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 single-parameter read with a full output schema, the description covers everything an agent needs: identity, return contents, data source freshness, and where it fits relative to search_titles. Nothing material is missing.

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 the slug parameter already documents its origin in search_titles with an example value. The description's mention of fetching by slug adds no syntax or format meaning beyond the schema, so the baseline 3 applies.

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 and resource (fetch a single Vooks title by slug) and enumerates what comes back (publisher description, age band, Lexile measure, running time, topics). It is clearly distinguishable from search_titles both by cardinality and by data source.

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 sequences the tool after search_titles and gives the condition that selects it ('when you need to say more about one book than the search result carries'). No explicit when-not-to-use case is stated, but the two-tool workflow is unambiguous.

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