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

Annotations already declare readOnlyHint=false, destructiveHint=false and openWorldHint=true, so the safety profile is known. The description adds genuine context beyond that — it discloses the return payload (extension result plus identifier) and that failures surface as validation/platform errors — but says nothing about permissions, duplicate handling, or whether the created asset is reusable across campaigns.

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 immediately followed by the return behavior and the scope boundary. No filler, though it is slightly terse for the amount of undefined parameter surface it covers.

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?

Knowledge that there is no output schema makes the return-value sentence valuable, and the scope boundary is a useful addition. However, with four parameters at 25% schema coverage and no annotations explaining mutation semantics, the description leaves field-level meaning and prerequisite context under-specified.

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 only 25% — only image_library_ids carries a description. The description's "using the supplied fields" adds no meaning for display_text, destination_url, or alternative_text, so an agent gets no guidance on what alternative_text is for versus display_text, or what URL constraints apply to destination_url.

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: creating an image extension in the account's Microsoft Ads asset library. It also distinguishes itself from the attach-to-campaign flow without naming the sibling explicitly, which is enough for an agent to tell it apart from create_google_image_extension or upload_image_creative.

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?

"Attaching the extension to a campaign is a separate operation" implies this tool only creates the library asset, and presumes image_library_ids already exist. There is no explicit statement of when to prefer this over create_google_image_extension or upload_image_creative, so usage is only implied.

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