Extend the last clip of a scene

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

Annotations already mark it as non-read-only, destructive, and idempotent, and the description adds valuable specifics: it spends credits when auto_confirm=true, and when auto_confirm=false it opens the prompt, fills it, screenshots, and cancels. The retry behavior and 'download instead of generate again' logic meaningfully explain what idempotency means in practice.

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?

The description is three dense sentences with no filler: main action, side effects and spending behavior, then retry semantics. It is front-loaded with the operation and keeps important caveats compact and readable.

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 7-parameter tool, the description covers the essential call path: last-clip target, continuation generation, download, credit spending, and retry behavior. The presence of an output schema means return values do not need to be described; the main remaining gaps are the roles of scene_url and job_id, which are relatively minor but not fully self-evident.

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 only 29%, so the description must compensate, and it does for several key parameters: auto_confirm, resume, after_clip_index, and the download behavior tied to output_dir. However, scene_url and job_id are never explained, so the compensation is incomplete.

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 description opens with a precise action: 'generates a 7-second continuation of the clip at after_clip_index' using 'Veo 3.1 - Lite', then states it downloads the result as a separate media file. This clearly identifies the verb, resource, and scope, and distinguishes it from sibling tools like flow_scene_add or flow_generate_video.

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 clear context: the operation applies specifically to the last clip, and the auto_confirm true/false split tells an agent what will happen in each mode. It does not explicitly name alternative tools or exclusion cases, but the scene-builder extension purpose is unambiguous enough for selection.

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