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

Annotations already declare openWorldHint=true and readOnlyHint=false, and the description explains WHY this read-like tool is not side-effect free: it consumes a daily search allowance when uncached. That extra quota/metering context is real value beyond the annotations. It stops short of describing any rate-limit specifics, pagination, or partial-result behavior.

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 short, front-loaded sentences with no filler: purpose first, cost behavior second, interpretation caveat last. The final sentence is a caution rather than invocation guidance, but it is brief and materially affects how an agent reports results, so it still 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?

An output schema exists, so return values need not be explained, and the description covers domain, source, and metering. However, for an 8-parameter, 5-required tool with zero schema descriptions, the definition leaves required inputs (brandId, dates, countries format/limits) entirely unexplained, which is a meaningful gap for correct invocation.

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% across 8 parameters (5 required), so the description carries the full burden and does not meet it. It never mentions brandId, source values, the countries array (max 30, ISO-2), the dateFrom/dateTo range, activeOnly, or advertiserId; only 'EU/EEA countries' loosely gestures at the countries parameter.

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 gives a specific verb+resource ('Search ... public ad libraries') plus scope qualifiers (Meta/TikTok, supported EU/EEA countries), so an agent immediately knows what domain this covers. It does not name or contrast the adjacent siblings (get_library_ad, save_library_ad, search_advertisers), which is what a 5 would require, but the search-vs-retrieve distinction is inferable.

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 hints at cost/context ('Uses a daily search allowance if uncached') and adds a caveat about interpreting results, but never states when to choose this over get_library_ad, save_library_ad, or search_advertisers, and gives no exclusions or prerequisites. Usage is implied rather than prescribed.

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