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

Annotations already declare it is a non-read-only, non-destructive, open-world mutation, so the safety profile is covered. The description adds the important scoping behavior that omitting campaign_id writes at account level — a genuinely consequential default. It says nothing about the 20-item caps, policy review outcomes, or partial-failure behavior, which the schema alone doesn't convey either.

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?

One sentence, front-loaded with the created resources and finished with the scoping rule. No filler or redundant restatement of the title.

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 6-parameter mutation tool with nested objects and no output schema, the description covers the essentials: what gets created, what it attaches to, and the account-wide fallback. Gaps remain around required-asset validation and what the call returns, but nothing an agent needs to avoid a wrong invocation is missing.

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 only 33%, but the description does cover the most semantically important parameter: campaign_id's omission semantics, which the schema leaves completely undocumented. The remaining params (call, callouts, sitelinks) are inferable from structure but get no textual treatment, and the description never states whether at least one asset type must be supplied.

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 (Create) plus the exact resource types (sitelinks, callouts, call asset) and the attachment target. An agent can tell this apart from google_ads_create_ad or google_ads_add_keywords, though it never names the closest sibling, google_ads_add_more_assets.

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 parenthetical 'or the whole account if campaign_id is omitted' gives a real selection rule, which is useful. However, there is no guidance on when to prefer this over google_ads_add_more_assets, no prerequisite checks (campaign must exist, asset must pass policy), and no when-not guidance.

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