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

Annotations already cover safety (readOnly, idempotent, non-destructive, closed-world). The description adds genuinely new behavioral context: data is cached, a last refresh time is returned, and crucially no ad-library refresh side effect occurs — information the annotations do not convey.

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 short sentences, zero waste, with the core purpose front-loaded and the non-obvious no-refresh guarantee second. Nothing could be removed without losing signal.

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 a rich output schema and full annotation coverage, return values and safety are well covered, and the caching/no-refresh behavior is spelled out. The only real gap is parameter-level detail, which is thin given 0% schema coverage.

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 neither brandId nor watchId is documented in the schema, and the description does not compensate — it only alludes obliquely to 'watch' and 'brand'. An agent gets no format, constraint, or lookup guidance beyond the raw types.

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 (Read), resource (cached ads for a watch), and scope (belonging to this brand). This clearly distinguishes it from siblings like list_ad_watches, create_ad_watch, get_library_ad, and search_library_ads without needing to open any schema.

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 phrase 'never triggers an ad-library refresh' implicitly signals when to prefer this tool over refresh-triggering alternatives, but no sibling is named and there is no explicit when-to-use/when-not-to-use statement. Usage must be inferred from the caching note.

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