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

Annotations already cover the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=true); the description adds real value beyond them: it says the call is a PREVIEW, that assets are validated for existence and field-type match, and that the result carries a plan_id. It slightly undersells the tension between readOnlyHint=false and 'returns a PREVIEW' by not saying whether anything is persisted server-side.

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?

Front-loaded: the preview/scope statement comes first, background second. Every sentence carries information, though the trailing Google Ads API docs URL is filler for an agent that cannot browse.

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?

Output schema exists, so return format need not be explained. However, for a draft tool in a draft→confirm pipeline, the description omits the follow-up step (confirm_and_apply with the plan_id) and does not state whether partial validation failures abort the whole batch. Those omissions are the main remaining gap.

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 links/field_type enum values and customer_id defaults are already documented. The description adds nothing about parameter format or the account-default behavior of customer_id; baseline 3 applies.

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 (draft linking), the exact resource (existing assets at account level) and explicitly contrasts with campaign/ad-group-level linking. An agent can distinguish this from draft_sitelinks / draft_callouts / draft_image_assets without opening any schema.

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 account-level semantics and eligibility (serves on campaigns with no same-type asset at campaign/ad-group level), which implies when to reach for it. But it never names an alternative or exclusion, and crucially does not say the returned plan_id must be passed to confirm_and_apply to actually apply — the single most important routing fact for a preview tool.

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