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

Adds real behavioral context beyond the annotations: it discloses that this starts a background job, that it costs credits, and that it returns a project id meant for wait_for_video_project. It does not cover plan/auth constraints or failure behavior, but the cost and async nature are the highest-value disclosures here.

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 with zero filler; the core action, the usage trigger, and the cost/async warning are all front-loaded in that order.

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 an output schema present, return values needn't be described, yet the description still flags the project id and the wait_for_video_project handoff. Combined with annotations covering the safety profile and a rich schema, nothing an agent needs to call this 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 80%, so per-parameter meaning (model defaults, script character limits, end_seconds ranges, file path format) is already fully documented in the schema. The description only echoes that an image and script are needed, adding no syntax or constraint detail beyond it. 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 ('Creates a creator-style spoken ad video') and names both required inputs (prepared image, text script), which distinguishes it from siblings like create_video_from_image and create_talking_photo that lack the script-driven dialogue element.

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 a clear activation condition ('Use when the image is ready and the dialogue should be generated from text') and routes the follow-up to wait_for_video_project. It stops short of naming an explicit alternative or a when-not-to-use case, so it lands just below the top band.

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