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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the agent knows it's safe. The description adds context that it returns 66 canonical books and specific fields (names, slugs, etc.), which is beyond the annotations. No contradictions.

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?

Two sentences: first describes what the tool does, second gives usage guidance. No unnecessary words, front-loaded with key information. Every sentence is essential.

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 list tool with two optional parameters and no output schema, the description is complete. It explains the returned fields and the tool's role in the workflow (providing identifiers before lookups). The annotations cover safety and idempotency, so no additional behavioral context is needed.

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 baseline is 3. The description adds value by explaining that 'language' affects localization of names, slugs, and abbreviations, and 'testament' allows filtering, reinforcing the purpose of the parameters beyond the schema's basic descriptions.

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 clearly states the verb 'Lists' and the resource '66 canonical Bible books'. It specifies the returned data: localized names, slugs, abbreviations, testament grouping, and chapter counts. It also distinguishes from sibling lookup tools by saying 'before calling lookup tools'.

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?

Explicitly says 'Use this when an agent needs valid book identifiers or localized display names before calling lookup tools.' This indicates when to use. Although it doesn't explicitly state when not to use, the context of sibling tools like get_chapter and search_bible implies the tool is for enumeration and identifier retrieval, not direct lookups.

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