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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=true; the description adds value beyond them by stating the return contract (extension result plus identifier, or a validation/platform error). It could go further on idempotency or duplicate handling, so not a 5.

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, front-loaded with the action and scope, with the second sentence carrying a non-obvious behavioral boundary. No filler.

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?

With no output schema, the description compensates by describing the return value and error modes, and it clarifies the attach-vs-create boundary. Complete enough to invoke correctly, though it omits any note on duplicates or account-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% and both parameters carry min/max constraints and item counts in the schema, so the schema does the heavy lifting. The description adds nothing beyond 'using the supplied fields', matching the baseline 3 for fully documented params.

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 structured snippet extension') plus the exact location ('Microsoft Ads asset library'), which cleanly disambiguates it from the Google equivalent (create_google_structured_snippet_extension) and from other Microsoft extension creators such as sitelink or callout.

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 closing sentence, 'Attaching the extension to a campaign is a separate operation,' gives clear scoping guidance about what this tool does and does not do. It stops short of naming the sibling tool to use for attachment or of explicitly contrasting with the Google variant, so it stops at 4.

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