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

Beyond readOnlyHint/openWorldHint, it discloses the non-obvious fallback resolution path, the country dependency of that scan, and the 1-credit cost — real behavioral context. It stops short of saying what happens when neither lookup succeeds (empty result vs. error).

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, none wasted: identity, the fallback rule, then cost. The most decision-relevant constraint (archive id may not be directly addressable) is front-loaded after the purpose.

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?

No output schema exists, so the description carries return-value burden, and 'Ad details' gives little sense of the payload shape. Otherwise it covers the identifier semantics, the fallback, and cost adequately for a 4-parameter read tool.

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 75%, so baseline is 3; the description adds genuine meaning for page_id by explaining it enables the archive-scan fallback rather than just being 'the advertiser's page id'. country and cache_max_age are left entirely to the schema, and the URL form of id is only in the schema.

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 and resource ('Ad details') plus scope ('one ad from the Meta Ad Library by its archive id'), which cleanly distinguishes it from the plural facebook_adLibrarySearch and facebook_pageAds siblings.

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?

Explains the key conditional: when Meta has no addressable archive node, pass page_id to trigger an archive scan. It gives clear context for the fallback and the cost, though it never states when to prefer a sibling search tool or when the call will fail outright.

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