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

Annotations already establish that this is a safe read-only operation, and the description adds useful behavioral context about library versus attachment scope, flat return shape, and the fact that unattached extensions do not serve. It does not discuss rate limits or ordering, but it goes meaningfully beyond the annotations.

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?

The description is four tight sentences, front-loaded with the core action and then adding scope and return-shape context. Every sentence earns its place without repetition or 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?

For a read-only list tool with full schema coverage and no output schema, the description provides enough context: what is listed, how scoping works, what fields are returned, and that unattached extensions do not serve. Only minor operational details such as result ordering or pagination behavior 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?

Schema coverage is 100%, so each parameter is already documented in the schema, including the adGroupId-over-campaignId precedence. The description reinforces the no-ID versus ID-based scoping model, but most parameter meaning is already carried by the schema, making the baseline 3 appropriate.

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 uses a specific verb and resource ('List ad extensions') and enumerates the extension types, so the tool's purpose is immediately clear. It does not explicitly name sibling tools such as msads_add_ad_extensions or msads_set_ad_extension_attachment, but the list/read nature is unambiguous.

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 clearly explains the key usage branches: no campaignId/adGroupId returns the account-wide extension library, while supplying either filters to attached extensions. It also notes that ad group attachments override campaign ones, which helps an agent choose parameters, though it stops short of naming alternative tools or explicit when-not scenarios.

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