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

Annotations provide no behavioral hints (all false), so the description carries the burden. It discloses that the operation blocks ('Blocks until done (1–3 min)') and costs credits, which are beyond annotations. However, it does not mention what the tool returns (no output schema) or any other side effects, leaving a significant gap for a tool that is not readOnly and is likely to be a long-running operation.

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 description is three sentences with no filler; the core action and key constraints are front-loaded. It efficiently communicates the blocking behavior, capability requirement, and cost. Slight jargon ('creator lip-sync') could be clarified, but overall it is well-organized and to the point.

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?

Given the tool's complexity (blocking, cost, capability requirement) and lack of output schema, the description covers the blocking duration, credit cost, and capability prerequisite, but it fails to describe the output format (e.g., video file/URL), which is critical for an agent to know how to use the result. It also does not mention fallback or failure behaviors. This incompleteness prevents a higher score.

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 100%, so each parameter already has a clear description. The tool description adds minimal semantic value by emphasizing that the image is a 'portrait' and the script is what the avatar speaks, but the schema already says 'presenter portrait' and 'the words the avatar speaks'. Thus the description does not meaningfully enhance parameter understanding beyond the 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?

The description uses a specific verb ('Render') with a clear resource ('TALKING-AVATAR / creator lip-sync clip') and inputs ('portrait image + a script'). It distinguishes itself from siblings like generate_video, generate_voice, and dub_video by focusing on lip-sync from a still image, giving the agent enough to differentiate without ambiguity.

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?

The description states prerequisites ('Requires the avatar capability (canAvatar in hermoso_capabilities)') and cost ('Spends credits'), which are useful conditions, but it does not explicitly state when to use this tool vs alternatives like generate_video or generate_voice, nor when not to use it. The context is implied but not made explicit.

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