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

Goes well beyond the annotations: discloses the 60-second self-terminating duration, the microphone requirement in the user's browser, the session_url return and what to do with it when no player is shown, and structured error semantics (unknown character -> list_characters with `talk` true; resting -> make_character_video still works). Annotations only cover the safety profile; the description carries the real behavioral burden.

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-loaded with the core action and duration before edge cases, and every clause carries information (duration, return value, error routing). It is dense rather than padded, though the error-handling tail makes it slightly longer than strictly needed for a one-parameter tool.

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 single-param tool with a full enum, an output schema, and annotations, the description supplies everything an agent needs: lifecycle, duration, return value usage, environment prerequisite, and both failure modes. Nothing material 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% and the enum enumerates every valid id, so the schema does the heavy lifting. The description still adds value by showing an example call and explaining how to validate an id (use one whose `talk` is true), which is meaning beyond the schema's plain 'a character id from list_characters'.

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 ('Open a live voice conversation with one bitHuman house character') and immediately distinguishes itself from siblings by naming list_characters for id lookup and make_character_video as the fallback. An agent can tell exactly what this tool does and does not do.

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 when-to-use context (user presses Start, speaks via microphone), a hard limit (60 seconds, then ends by itself; call again for another), and a when-not path: if the service is 'resting', use make_character_video instead. The alternative is named with the condition that selects it.

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