start_video

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

With no annotations, the description carries the full burden and largely meets it: it discloses the asynchronous job_id contract, provider defaults, how duration_seconds and aspect_ratio are re-mapped per provider, that duration_seconds is *rejected* for fal, and that options are merged into the provider request. It omits auth requirements, rate limits, and prompt constraints, so not a 5.

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 first sentence front-loads the action and the async contract, followed by compact per-provider bullets. It is dense but every line carries operative detail; only minor trimming is possible.

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, no-annotation mutation tool this is thorough, and the job_id/polling contract plus provider quirks are covered. An output schema exists so return values need not be described, but there is no mention of validation limits or failure behavior, keeping it just short of complete.

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 0%, so the description must compensate, and it does: provider enumerates the three backends with defaults, aspect_ratio/duration_seconds translation is spelled out per provider, duration_seconds' fal constraint is documented, options is defined as provider-specific merged keys with examples, and input_image's accepted formats (path/URL/data URI) are given. This adds meaning far beyond the bare 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?

States a specific verb+resource ('Start a video generation job') and immediately distinguishes the two modalities (text-to-video vs image-to-video via input_image). It also names the sibling it hands off to (check_video), so an agent can separate start from poll without opening either 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?

Gives explicit workflow guidance: this tool returns a job_id immediately and check_video(job_id) must be called to wait for the result. It also provides per-provider selection guidance with defaults. It stops short of stating when *not* to use it (e.g. vs. generate_image/generate_audio), so a 4 rather than 5.

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