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

Annotations already declare destructive=true, idempotent=false, and openWorld=true, so safety is covered. The description usefully adds that the operation returns a tracked task plus a playable result when complete, and that the model must support the operation — but does not restate idempotencyKey retry semantics that live only in the schema.

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 sentences, front-loaded with the operation, then the model prerequisite, then the outcome. Minor redundancy between 'a catalog model that supports upscale_image' and 'Use get_model_catalog', but nothing wasteful enough to harm selection.

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 an output schema present and rich annotations, the description needn't explain returns, and it covers the model dependency and result semantics. For a 21-parameter, nested-object tool the coverage is adequate, though it could say more about the modelSettings/mediaInputs flow.

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 81%, so the schema itself documents most parameters. The description only reinforces the model-selection dependency and says nothing about scaleFactor, resolution, or cost controls beyond what the schema already states, so baseline 3 is 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?

States a specific verb+resource ('Upscale an existing image') that cleanly separates it from siblings like upscale_video, edit_image, and enhance_video_media. An agent can identify the operation without opening the schema.

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?

Explicitly directs the agent to get_model_catalog to select a supported model and its settings, which is the key prerequisite. It does not, however, contrast itself against near-alternatives like edit_image or enhance_video_media, so when-not-to-use is left to inference.

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