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

Annotations only declare openWorldHint, non-idempotent and non-destructive; the description adds substantial context beyond that — dual billing rails (OAuth site credits vs API key USD wallet), a concrete price floor (101 credits per second with the default model), and a two-step quote-then-approve protocol. It does not disclose the return shape (e.g. whether a job id is returned and must be polled via get_job), which is the one notable behavioral gap.

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?

Purpose is front-loaded in one sentence, then billing/approval rules follow in a logical order. The final sentence is dense with billing jargon but every clause carries actionable information; nothing is padded.

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 an 8-parameter, nested-object, open-world generation tool with no output schema, the description covers inputs, billing modes, and the cost-confirmation protocol well. What it omits is post-call behavior — whether this submits an async job and what the response contains — which matters given the sibling get_job exists.

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 ordering semantics the schema does not: pricing parameters are only to be set after the user confirms a quote, and max_credits/max_usd are mutually tied to the auth mode. That cross-parameter relationship is genuine value beyond the field descriptions.

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 opening sentence states a precise verb+resource+mechanism: animate a character picture using the motion of a separate video. That combination of inputs (still image + motion source clip) clearly separates it from siblings like change_pose, create_video_from_references, and compose_video, which an agent can distinguish 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?

The description gives real workflow guidance for the approval/quote cycle (omit approval to get a quote, then confirm max_credits or max_usd), which is useful. However, it never says when to pick this over the many sibling motion/video tools, and gives no exclusions or prerequisites for the source inputs.

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