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

Adds a great deal beyond the annotations: output is a watermarked preview, the photo is placed in a fixed layout rather than AI-generated or edited, usage is free with a 3-per-client-per-day limit, the offer string is rendered verbatim, and failures return an error with no image. None of this conflicts with readOnlyHint=false / openWorldHint=true / idempotentHint=false.

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?

Front-loads what is produced and at what size, then requirements, then optionals, then behavior. Dense but nearly every clause carries information; the closing failure sentence is slightly redundant given the error path is obvious, and the shape/type restatements repeat the schema.

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 still names exactly what comes back (watermarked preview image URL plus headline, body and CTA), so an agent knows the return shape. Input format, size limits, rate limits and failure behavior are all covered for a 4-parameter generative tool.

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 the baseline is 3, but the description adds real semantics: the offer is used verbatim and only applies alongside an occasion, and product means name plus short description. The 40-character cap and file-type/size limits are duplicated from the schema but reinforce correct input construction.

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 (turn a photo into) and a concrete artifact: a finished 1080x1080 social ad image with headline and CTA plus matching copy. The size, output format and inputs make it clearly distinct from the sibling generate_ad_headlines, which returns text only.

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?

Gives clear conditions for the optional parameters (occasion for a sale badge; offer only meaningful together with an occasion) and states the input preconditions for photo_url. It stops short of explicitly routing between this tool and generate_ad_headlines, so the agent must infer that this one produces the full creative.

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