get_ad_details

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

No annotations are provided, so the description carries the full burden. It discloses that the keyword is used to re-find the ad, the country default is 'ALL', and includes a critical behavioral trait: 'ads not delivered in the EU have eu_total_reach=null (Meta's design)'. This goes beyond basic purpose to inform the agent of important edge cases.

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?

The description is well-structured with 'Args' and 'Returns' sections, and a note. Every sentence adds value: purpose, parameter descriptions, return structure, and a crucial behavioral note. No redundant or vague statements.

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?

Given the tool has 3 parameters, no output schema, and moderate complexity, the description covers all necessary aspects: what the tool does, how to use parameters, the return value structure, and an important null case. It is fully self-contained 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 coverage is 0% (no descriptions in input schema), so the description must explain each parameter. It does so effectively: keyword is the search keyword used earlier, library_id is from search_ads, and country is ISO-2 or 'ALL'. This adds valuable context beyond the schema's type and title.

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 clearly states 'Fetch one ad's EU/UK reach + per-country/age/gender breakdown', specifying the verb 'fetch', the resource 'ad', and the detailed data returned. It distinguishes from sibling tools 'search_ads' (which searches for ads) and 'session_status' (which checks session) by focusing on fetching details for a single ad.

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 description provides explicit prerequisites: keyword must be the same as used in search, and library_id must come from search_ads. It also explains the purpose of each argument and the default for country. While it does not explicitly state when not to use, it implies usage after search_ads, which is sufficient given distinct sibling tools.

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