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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds genuinely useful context beyond that: results are cached, it returns a last-refresh timestamp, and it does not trigger an ad-library refresh, which is a meaningful side-effect guarantee.

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 tightly written sentences with zero waste. The core purpose is front-loaded and the side-effect guarantee follows logically.

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?

An output schema exists, so return values need not be re-explained, and annotations cover the safety profile. For a simple cached read, the description supplies the one thing structured data cannot: that no refresh is triggered. Only minor gaps (no alternative-tool routing, no param detail) remain.

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 the description must carry the param burden. It partially compensates by conveying the brand-scoped relationship between brandId and watchId ('a watch belonging to this brand'), but adds no format, validation, or disambiguation detail beyond what the schema's patterns and uuid format already imply.

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') and resource ('cached ads for a watch belonging to this brand'), which clearly distinguishes it from the mutating siblings create_ad_watch and delete_ad_watch. It does not, however, differentiate itself from closely-related read siblings like list_ad_watches or get_library_ad, leaving some ambiguity about which read path to pick.

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' implies when to use it (when you want cached data avoid a costly refresh), which is useful implied usage guidance. But there is no explicit when-to-use or when-not-to-use statement, and it never names an alternative tool, so the agent must infer the selection criteria.

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