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

Annotations cover the safety profile (non-readOnly, non-idempotent, non-destructive), and the description adds material context: credits are spent per clip, the call returns a job rather than the finished clip, and omitting the quote downgrades the call to a cost estimate. It stops short of stating credit-refund or failure behavior, but the disclosed traits are substantial.

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 tight sentences, front-loaded with what it does, then the credit implication, then the hard prerequisite. No filler and every clause carries operational information.

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, the description correctly explains the return value (a job whose completion links the clip) and the cost-only fallback path. For a 7-parameter, non-idempotent generation tool, nothing an agent needs to invoke it correctly is missing.

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 100%, so the schema already documents every parameter including the quote's 'exactly this request' semantics. The description reinforces the quote requirement and start_image usage but adds no syntax or format detail beyond the schema, so the baseline 3 applies.

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 and resource ('makes a video clip from a prompt, optionally beginning on a still') and describes the async job contract plus the returned clip link. It is clearly distinguishable from sibling generators like ugcfans_make_image or ugcfans_make_ad.

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 prescribes the workflow: call ugcfans_estimate first and pass its quote, otherwise the call only returns cost and makes nothing. It also points to ugcfans_list_models for per-model pricing, giving the agent both prerequisites and the right companion tools.

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