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

Annotations already carry readOnlyHint, idempotentHint, and openWorldHint, lowering the bar. The description adds value beyond annotations by disclosing the return payload and, importantly, the exclusion behavior that author names are omitted — a non-obvious trait an agent must know before calling. No contradiction: 'Fetch' is consistent with readOnlyHint=true.

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 tight sentences with zero filler. The verb+resource and primary behavior are front-loaded, the abstract-work concept is stated next, and the exclusion with alternatives closes it out. Every sentence earns its place.

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?

Output schema covers return values, the sole parameter is fully documented in the schema, and annotations carry the safety profile. The description completes the picture with the work-versus-edition distinction and the author-name exclusion. Nothing an agent needs to call this correctly 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% — work_id's format (OL…W), required status, and prefix-stripping ('/works/' is stripped) are fully documented in the schema. The description merely echoes the OL…W format without adding syntax or semantic details beyond the schema, so the baseline 3 is appropriate.

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: 'Fetch a work by Open Library Work ID (OL…W)'. Clearly differentiates from siblings by explaining that works are the 'abstract book concept independent of any specific edition', pointing away from get_edition and get_edition(s). The returns list (title, description, subjects, cover IDs, author IDs) makes the tool's scope unambiguous.

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?

Provides an explicit exclusion with named alternatives: 'author names are not included — use openlibrary_get_author or openlibrary_search_books for names.' The work-vs-edition distinction also implicitly routes the agent toward get_edition when a specific physical edition is wanted, though it does not name that sibling explicitly. Clear context with one explicit exclusion, but not a full when-to-use enumeration.

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