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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: the two return states ("rendering" vs. finished video shown inline) and the fact that the call is free. It omits failure behavior for an unknown or expired generation id, which keeps it out of the top band.

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 with no filler; the dependency on animate_image is front-loaded and each sentence contributes distinct information (source of the id, return states, cost).

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 and no annotations covering returns, the description correctly explains the two possible outcomes, which is the key thing an agent needs to branch on. It is close to complete for a one-parameter polling tool, missing only error/expiry handling.

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 0% for the single generation_id parameter, so the description must compensate. It implies the id originates from animate_image, which is helpful context, but it never names the parameter or explains that it is the generation identifier returned by that call, so the mapping is left partly to inference.

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 — checking on a video — and explicitly ties it to the sibling tool that produces the resource ("a video started with animate_image"). An agent can distinguish this polling tool from animate_image, generate_image, and the show/list siblings without opening any 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?

It clearly states the trigger condition: use this after a video has been started with animate_image. It does not, however, give exclusions or practical polling guidance (e.g., how often to re-check), so it stops short of the full when/when-not treatment.

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