Estender vídeo

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

Annotations only declare readOnly=false, openWorld=true and destructive=false; the description adds the material behaviors: real cost is read before generating (~10 credits), the model may be silently overridden by Flow with a warning in the response, output always lands in a fixed local path, and the call is slow (~1-3 min) and often returns 'in progress'. This is exactly the context annotations cannot convey.

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?

Front-loaded with purpose and the sibling alternative, and every later sentence adds operational value (path, model override, cost, latency). It is dense and slightly repetitive – the Flow model override is stated twice – but nothing is filler.

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?

No output schema exists, yet the description covers where the artifact is written, that generation is asynchronous and must be confirmed via flow_status, and what the response does when the model differs. For a mutation tool with an open-world hint, an agent has everything needed to call it and follow up correctly.

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 coverage is 100%, so the baseline is 3; the description earns a point by warning that the requested model may not be honored and by naming the credit cost associated with the default model. That said, much of the model caveat is already repeated in the schema's own modelo description, so the added value is modest.

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 ('Continua um vídeo ou uma cena já estendida'), specifies the +~7s scope and the .mp4 output, and explicitly separates it from the sibling flow_video_longo for long multi-segment videos. An agent can tell what this does and what it is not without opening a schema.

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 routes long multi-part videos to flow_video_longo and tells the agent to poll flow_status until the save completes on Claude Desktop. It does not contrast against flow_gerar_video (starting a new video vs continuing), which is the other plausible alternative, so it stops short of full when/when-not coverage.

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