Extend Video

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

The description adds meaningful behavioral context beyond the annotations: it discloses the asynchronous nature and the polling mechanism, which is critical for the agent. It also states the effect ('generating additional seconds of motion'), consistent with readOnlyHint=false. The description complements the annotations without contradicting them.

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 concise and well-structured: a one-sentence purpose, a one-sentence async note, and a compact argument list. Every sentence earns its place, with no redundancy or fluff.

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?

The description is complete for a tool with three required parameters and no output schema. It explains the async workflow and explicitly directs the agent to xbrush_get_request for polling, which is essential. The model-selection hint and duration range cover the key usage details. Given the moderate complexity, nothing critical 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 100%, so the baseline is 3. The description repeats the parameter details but adds marginal value with example model names and a direct pointer to xbrush_list_models. Since the schema already documents ranges and formats, the description does not significantly enhance parameter understanding beyond the schema.

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: 'Extend an existing video by generating additional seconds of motion.' This uses a specific verb ('extend') and resource ('existing video'), and the scope is well-defined. It naturally distinguishes from siblings like xbrush_video_generate, xbrush_video_upscale, and xbrush_video_retake.

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 provides clear usage context by noting that the tool 'Submits async — poll the returned request_id with xbrush_get_request,' which tells the agent what to do after invocation. It also gives model selection guidance via 'See xbrush_list_models(category='video'), featureType 'extend'.' However, it does not explicitly contrast with alternatives like video_generate or video_upscale, so it lacks explicit when-not-to-use guidance.

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