Get one ad in full

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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint, and destructiveHint=false. The description adds meaningful behavioral detail about the comprehensive nature of the response: 'every creative, all copy variants, the full destination URL and any transparency data'. This goes beyond what the annotations alone convey and sets expectations for output completeness.

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 sentences, no filler. The first sentence states action and coverage; the second gives usage guidance. The most important information is front-loaded and every sentence 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?

For a simple single-id fetch tool, the description covers what, when, and why, while the input schema covers parameters and the output schema covers return structure. Annotations cover the safety profile. Nothing essential is missing for an agent to select and invoke this tool correctly.

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 100%, so the schema already documents library_id and country. The description itself does not add parameter-level semantics beyond referring to 'Ad Library ID', which matches the schema. Baseline 3 is appropriate because the schema carries the load.

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 opens with a specific verb and resource: 'Fetch a single ad by its Ad Library ID'. It enumerates the scope of what is returned ('every creative, all copy variants, the full destination URL and any transparency data'), which clearly separates it from bulk search tools and narrower sibling tools like view_ad_creative or get_eu_transparency.

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 explicitly says 'Use this after search_ads when one ad is worth studying properly', giving clear when-to-use context and naming the relevant sibling workflow. It does not enumerate when-not-to-use cases or alternative tools for narrower lookups, but the placement and rationale are clear enough.

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