Generate a video from a still

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

The description adds significant behavioral details beyond the annotations: it explicitly says 'SPENDS the account's credit — video costs several times an image,' and explains the asynchronous nature ('Takes ~1-3 minutes, so it usually returns a queueId...'). These details are not present in the annotations (readOnlyHint, openWorldHint, etc.) and are crucial for the agent to manage cost and expectations. No contradiction with annotations.

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 concise—three or four short sentences—with the purpose stated first. Each sentence adds value: purpose, cost, async behavior, and duration options. It is front-loaded, allowing the agent to quickly grasp the core function and key operational caveats. There is no redundant or filler content.

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?

Given the tool's complexity (8 params, no output schema), the description covers essential operational context: it mentions credit cost, asynchronous queueId retrieval, and duration variants with tier-gating. It does not describe the return object structure in detail, but it mentions queueId, which is sufficient for the agent to know what to expect. The schema handles parameter details, so the description is complete enough for this context.

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?

The input schema provides descriptions for all 8 parameters (100% coverage), so the baseline is 3. The description itself only repeats duration information ('Durations: 5, 6.5 or 7.5 seconds (7.5 is tier-gated)') which is already in the schema. It does not add any extra semantic meaning about parameters like prompt, style, or quality, so it meets the baseline but does not exceed it.

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 clearly states the tool's purpose: 'Animate an existing still creation into a short clip.' This specifies a verb (animate), a resource (still creation), and the output type (short clip), effectively distinguishing it from sibling tools like generate_image or generate_similar. The title 'Generate a video from a still' reinforces the purpose without ambiguity.

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?

The description provides clear context: use this tool when you have an existing still creation and want to animate it into a video. It also advises that the operation takes 1-3 minutes and typically returns a queueId to collect with check_generation, which guides follow-up behavior. However, it does not explicitly mention alternatives or state when NOT to use this tool in favor of other generation tools, so it falls short of a 5.

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