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

Annotations already declare readOnly=false, openWorld=true and destructive=false, so safety framing is covered. The description adds real value by scoping the write to the asset library rather than a campaign and by disclosing the outcome envelope (extension result plus identifier, or a validation/platform error). It does not detail rate limits, permissions, or what validation rules apply beyond those in the schema.

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 tight sentences, front-loaded with the action and scope, followed by the return contract and the boundary against the attach operation. Every sentence carries information an agent needs and there is 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 usefully states what is returned and that failures surface as validation or platform errors. Combined with full schema coverage this is nearly complete; only account-context assumptions and any post-creation workflow detail are left implicit.

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?

All four parameters are required and the schema covers them at 100%, including length constraints, so the schema carries the semantics. The description only says "using the supplied fields" and adds no meaning about how url, link_text or the description lines are used or validated, 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?

The description names a specific verb and resource (create a sitelink extension) plus its scope (the account's Google Ads asset library), which separates it from the Microsoft sitelink sibling and from the other extension-type creators. It also explicitly distinguishes itself from the attach step by noting that "Attaching the extension 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?

It gives clear context for when to use this tool (to populate the asset library) and explicitly points out that attaching to a campaign happens elsewhere, which is a genuine alternative-routing hint. It stops short of naming the sibling tool to use for attaching or stating prerequisites, so it is clear but not a full when/when-not statement.

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