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

Annotations already declare the operation is non-read-only, non-idempotent and open-world, so the safety profile is covered. The description adds genuinely useful behavior: it is an asynchronous job (mirroring kling_text_to_video), costs ~5 credits per 5 s, and requires a frontal face within 60 s. It does not say how results are retrieved, which holds it back from 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?

Three tight sentences with zero filler; the core action, the hard input constraints, cost, async semantics and endpoint are all front-loaded and each earns its place.

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 an async, no-output-schema job tool, the description covers action, constraints, cost and job semantics, which is enough to invoke it correctly. The only gap is that it implies result polling via kling_get_task without saying so explicitly.

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 video/audio/email are already fully documented in the schema (including the kling_upload_asset recommendation and multi-account guidance). The description only adds the 60 s / frontal constraint on the video input, so baseline 3 is appropriate.

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 action and resource: make the face in a video speak an audio track. It also pins the input scope (up to 60 s, frontal), which differentiates it from kling_add_sound and kling_avatar_video without opening their schemas.

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 60 s / frontal constraint implicitly tells the agent when this tool is applicable, and 'A job, like kling_text_to_video' signals the async submission pattern. However, it never names an alternative (add_sound, avatar_video) or states when not to use it, so routing 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.