animate_image

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

With no annotations, the description carries the burden and does substantial work: it discloses that the image is uploaded as a data URL, that some providers require a public HTTPS URL, that omitting generate_audio defers to the provider, and that HeyGen Video 1 mandates audio. It says nothing about cost-related behavior (allow_paid, max_cost_usd) or what dry_run actually returns, which for a paid generation call is a meaningful omission.

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?

Four dense sentences, front-loaded with the core action and capability gate, then the audio and upload caveats. No filler, though the cost/permission flags are crowded out by provider-specific trivia.

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?

A 13-parameter, no-annotation, no-output-schema tool with zero schema descriptions needs far more, especially around the paid-generation controls (allow_paid, max_cost_usd) and output handling. The description covers the image-upload path and audio semantics but leaves the majority of the surface unexplained.

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 0% across 13 parameters, so the description must compensate and largely does not. It adds real meaning only for generate_audio and the image input (data URL vs. public URL); prompt, duration, resolution, aspect_ratio, model, output_dir, filename, dry_run, allow_paid, and max_cost_usd are all undocumented in both schema and description.

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: animating a local image as the first frame of a video request, which is distinct from a plain text-to-video generate_video or a static edit_image. It never names a sibling explicitly, so the differentiation is inferable rather than stated.

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 a hard precondition (only for models publishing supported_frame_images.first_frame) and a provider-specific caveat about audio, which constrains usage. However, it never says when to choose this over generate_video or edit_image, nor what to do when the model capability check fails, so the when/when-not guidance is only implied.

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