luma_extend_video

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

No annotations are provided, so the description carries the full burden. It discloses the key behavior ('adding more motion and content after the original video ends') and mentions the return of a Task ID, implying an asynchronous task. However, it does not mention potential side effects, requirements, or whether the original video is modified, which would be valuable for a generation tool.

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 well-structured with a clear intro, a bulleted 'Use this when' list, and a brief 'Returns' section. It is slightly verbose but every sentence earns its place by clarifying purpose and usage. No filler content.

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 4-parameter tool with output schema, the description is fairly complete: it covers purpose, usage scenarios, and return values. It lacks explicit mention of asynchronous behavior or a comparison with luma_extend_video_from_url, but the 'Task ID' and 'previous generation' hints mitigate this. Given the moderate complexity, it is adequate.

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?

Input schema has 100% description coverage, so the baseline is 3. The description adds no extra parameter details beyond what the schema already defines for prompt, video_id, callback_url, and end_image_url. It does not repeat or expand on schema descriptions, so no additional value.

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 clearly states the tool's function with a specific verb and resource: 'Extend an existing video with additional content.' It distinguishes from siblings by specifying 'previously generated video' and 'after the original video ends,' which aligns with the tool name and separates it from luma_extend_video_from_url.

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?

Provides explicit 'Use this when' guidance with three concrete scenarios: video too short, continue story/motion, build longer piece by piece. It does not mention when to use alternatives like luma_extend_video_from_url, but the context of 'previously generated video' implies this is for existing Luma generations.

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