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

Annotations declare readOnly=false, idempotent=true, destructive=false, so the safety profile is already covered. The description still adds real behavioral value: the output is a video URL that plays inline and is labelled AI character, and speech is rendered verbatim at roughly 15 seconds for 3–200 characters. It does not mention latency or generation cost, which is the remaining gap.

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?

Three short sentences, front-loaded with the core action before the parameter hints. The '3 to 200 characters' restates the schema's minLength/maxLength, a minor redundancy, but nothing else is wasted.

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?

With an output schema present, the description need not explain return values, yet it still notes the video URL and inline playback. Combined with the character-id source and length/duration guidance, an agent has enough to call it correctly; only sibling routing guidance is thin.

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% and the enum is fully enumerated, so baseline would be 3. The description goes modestly beyond the schema by clarifying that 'text' is spoken word for word and that its 3–200 character range corresponds to about 15 seconds of speech, which is genuinely new information an agent can use when composing input.

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: 'Make a short video of one bitHuman house character saying the given words, in its own voice.' An agent immediately knows this produces a rendered video rather than a live exchange. It does not explicitly contrast with talk_to_character, so the sibling differentiation is only implicit.

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?

It gives one concrete usage pointer — 'Use a character id from list_characters' — which tells the agent where valid ids come from. However, it offers no when-to-use vs. when-not guidance and never names talk_to_character as the alternative for interactive speech, so selection between siblings is left to inference.

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