extend_video

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

With no annotations the description carries the full burden and does so well: it discloses the return mechanism (job_id consumed by get_video, result is the new part), the underlying model, URL provenance constraints, and a cost-safety warning that a timeout retry pays twice. Cost, failure handling and output routing are all covered.

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-loads the purpose, then layers model, return value, constraints and failure handling in a logical order, with every sentence carrying information. Minor redundancy: the hard-coded model string and the estimate_only 'nothing is charged' point are already present in the schema descriptions.

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 and no annotations, so the description must explain returns and mutation-side effects; it does both by routing results through get_video via job_id and warning about double-billing on retry. Nothing an agent needs to invoke 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 coverage is 100% so the baseline is 3, but the description adds real meaning beyond the schema: 'Links must be https; links returned by this server work' clarifies acceptable video_url values, and the get_video/job_id note frames video_url as an existing job artifact. It does not add much for duration or prompt beyond what the schema already states.

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 with a concrete behavior: 'Continue a video from its last frame, so a scene keeps going', plus an illustrative example. This operationally separates it from start_video (new video), edit_video (alter existing), and upscale_video/motion_control without needing to name them.

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 clear context for when to reach for it (continuing an existing scene) and an example, and adds explicit retry guidance for timeouts. It does not, however, explicitly contrast itself with siblings like start_video or edit_video, leaving some selection inference to the agent.

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