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

Annotations already declare a non-read-only, non-destructive, open-world write. The description adds value beyond them by disclosing outcome semantics ('Returns the extension result and available identifier, or a validation/platform error') and that the asset is not attached to any campaign by this call — useful, non-obvious context for a mutation tool.

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 tight sentences: the action and scope come first, then return behavior and the attach caveat. No filler and nothing restated from the annotations.

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 write tool with no output schema, the description covers what is created, what comes back, and what is not done (attachment). Remaining gaps are minor — which account identifier the call implicitly targets and any per-account extension limits are unstated, but the schema carries the field-level constraints.

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 100% — nested offering fields, the 3-8 item bounds, length limits, and the price_qualifier enum are all in the schema. The description adds only 'using the supplied fields', which conveys nothing beyond the schema, 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 and resource ('Create a price extension in the account's Microsoft Ads asset library'), which cleanly separates it from the many sibling extension-creation tools for Microsoft, Google, and other asset types. It also disambiguates library creation from the separate attach step.

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?

Explicitly scopes the tool to asset-library creation and states that 'Attaching the extension to a campaign is a separate operation', which prevents the common misuse case. It stops short of naming the sibling that performs the attach, so the agent must infer the follow-up tool.

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