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

Annotations declare a non-read, non-idempotent, non-destructive but closed-world operation; the description adds behavior beyond that by disclosing the result shape (the film plus its first revision) and the cost profile (free of credits). It does not explain reversibility or the failure mode when preconditions fail, but the added cost and return details are meaningful.

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?

Two sentences, no filler, front-loaded with the transformation and its payoff before the constraint list. Every clause carries an actionable fact (output, preconditions, size limit, 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, the description correctly covers the return value (the film and its first revision), the input preconditions, and cost. What is missing for a job-oriented sibling set is whether the call is synchronous or job-backed and how to follow up if the film needs further editing.

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?

There is a single parameter with 100% schema description coverage, so the schema already explains that 'ad' is an ad id from a finished ugcfans_make_ad job. The description restates the 'must be finished' constraint but adds no format or syntax detail beyond the schema, making 3 the correct baseline.

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: converts a finished video ad into an editable film, and names the downstream benefit (captions and end card become editable). It implicitly separates itself from ugcfans_make_launch_film and ugcfans_make_site_sting by naming the source artifact (a finished ad), but never routes the agent between those alternatives explicitly.

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?

Gives concrete preconditions for use: the ad must be finished, must not already be a film, must be video, and at most 96 MiB. That is real context for when the call will succeed, though it stops short of naming an alternative tool or describing the case where the ad does not meet these conditions.

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