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

Annotations only declare the generic mutation profile (readOnlyHint=false, destructiveHint=false, openWorldHint=true); the description adds real value by describing the outcome surface — returns the extension result plus available identifier, or a validation/platform error. It does not mention permission requirements or platform-side quota behavior, which is the main remaining gap for an open-world write.

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 short sentences, front-loaded with the action and scope, then the return behavior, then the scoping caveat. 'Using the supplied fields' is slightly redundant filler, but nothing else is wasted.

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 two-parameter create tool with a fully documented schema and no output schema, the description covers action, scope, return shape, error behavior, and the downstream attach step. Only permissions and roughly what the identifier looks like are unaddressed.

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%, with the nested price_offerings cardinality (3-8) and the price_qualifier enum already documented in the schema. The description only says 'using the supplied fields' and adds no meaning about qualifier semantics or offering constraints, so the 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+resource ('Create a price extension') and pins the scope to the account's Google Ads asset library, which separates it from the many sibling extension creators at Microsoft and from the Google sitelink/callout/image variants. It also preempts the most likely confusion by saying attachment to a campaign is a separate operation.

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?

Gives clear context for when this is the right call (building an asset-library extension) and explicitly carves out the follow-up step ('Attaching the extension to a campaign is a separate operation'), which steers the agent away from expecting campaign-level effect. No named alternative tool is offered, so it falls short of a 5.

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