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

The annotations already declare this is a mutation (readOnlyHint=false), open-world, and non-destructive. The description adds valuable behavioral context by stating that it returns the extension result and available identifier, or a validation/platform error, and that attaching is separate. It does not describe permissions or side effects in the asset library, so it is not exhaustive.

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 three tight sentences with no filler: it front-loads the creation action, then the return behavior, then the separate-attachment boundary. Every sentence contributes useful information.

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?

There is no output schema, and the description usefully explains the return value and error behavior. However, for a four-parameter mutation tool with only 25% parameter coverage, the description omits prerequisite details and parameter-level guidance that an agent may need to invoke it correctly.

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 description coverage is only 25%, with image_library_ids documented but display_text, destination_url, and alternative_text left undocumented in both schema and description. The phrase 'using the supplied fields' adds no meaning, so the description fails to compensate for the low coverage.

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 states a specific verb and resource — creating an image extension in the Google Ads asset library — and clearly distinguishes this from attaching the extension to a campaign. The tool name and description are specific enough to separate it from sibling extension-creation tools such as create_google_sitelink_extension or create_microsoft_image_extension.

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 a useful usage boundary by noting that attaching the extension to a campaign is a separate operation, which tells the agent this tool only creates the asset. It does not explicitly name alternative tools or when to choose a different extension type, so it falls short of full when/when-not/alternative guidance.

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