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

Annotations already declare non-readOnly, openWorld, non-idempotent, non-destructive. The description adds real value beyond that: the ≤5MB JPEG/PNG/GIF constraint, the confirm=false dry-run mode, and the crop/pad transform behavior that modifies the source image. It does not discuss auth or rate limits, but the added operational context is substantial.

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 purpose and return value, then proceeds through format limits, aspect, fit, pad_color, and dry-run in a compact, information-dense way. Slightly long but nearly every clause adds decision-relevant detail.

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 7-param mutating upload tool with an output schema (so return shape need not be explained), the description covers the tricky parameters and safety constraints well. Only the undocumented name/image_url/customer_id params keep it from being fully complete.

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 0%, so the description must carry the load, and it does for the non-obvious params: aspect (with ratio values and what each ratio is for), fit (cover vs pad semantics and edge handling), pad_color (transparent/#FFFFFF with the wide-logo case), and confirm (dry-run). It leaves name, image_url, and customer_id undocumented, which is a minor gap given those are self-evident.

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 ('Uploads an image to the Google Ads asset library') and names the return value (asset resource_name). This distinguishes it from the numerous sibling uploaders (upload_image, upload_meta_image, upload_tiktok_image, gbp_upload_photo) by pinning the destination to Google Ads assets.

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?

Explains downstream consumers (PMax images, responsive display ads, image extensions) and gives decision guidance for fit='cover' vs fit='pad' with concrete scenarios. It stops short of naming when NOT to use it or pointing to sibling uploaders for other platforms.

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