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

Beyond the annotations (which only mark it as a non-readonly, open-world, non-idempotent write), the description discloses the cost model (from 25 credits per second with the default model), two separate billing wallets depending on auth mode, and a mandatory quote-then-confirm approval handshake. These are exactly the behavioral facts an agent needs before spending a user's money.

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: capability first, cost model second, approval workflow third — properly front-loaded with no filler. The billing sentence is dense but every clause carries information the agent cannot get from the structured fields.

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 9-parameter, open-world, nested-object generation tool with no output schema, the description never says what comes back — a finished video, or (given sibling get_job) a job handle that must be polled. It also doesn't mention reference image limits or ordering beyond what the schema says. Cost and approval are well covered, return behavior is not.

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 would be 3, but the description adds cross-parameter semantics the schema only states in isolation: the sequencing where no approval yields a quote, and only a confirmed quote unlocks max_credits (OAuth) or currency=USD with decimal max_usd (API keys). It reinforces rather than contradicts the per-field schema text.

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 names a specific verb and resource plus the distinctive capability: making a video that preserves characters, products, outfits or places from reference pictures, driven by a shot description. That clearly separates it from plain create_video, but the sibling is never named, so the agent must infer the boundary from the phrasing alone.

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 explicit procedural guidance: omit approval to obtain a quote first, then confirm max_credits for OAuth or currency=USD plus max_usd for API keys, and it states which billing path applies to which auth mode. It does not cover when to choose this tool over create_video, extend_video or compose_video, which is the remaining gap.

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