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

With no annotations at all, the description carries the full disclosure burden and does add useful behavior: the added audio is truncated to the video's length, and mode controls whether the original track is discarded or blended. It omits important operational details such as whether the result is a new asset or an in-place modification, what happens on audio/video length mismatch beyond truncation, and any error or format constraints.

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, then the mode decision, then the truncation and volume behavior. No filler or redundant restatement of the tool name.

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 four-parameter, two-required mutation tool with no annotations and no output schema, the description covers the essential semantics an agent needs to call it correctly. The main missing element is what the call returns or where the resulting video is delivered, which is not covered by an output schema.

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%, so the description must compensate, and it does for the two non-obvious parameters: mode's two accepted values are defined semantically, and audio_volume is given its 0.0-2.0 range and scaling meaning. The remaining two parameters (video_url, audio_url) are self-describing by name, leaving no significant gap.

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 gives a concrete verb and resource ("Put a soundtrack on a video") and immediately names the two operating modes, so the tool's function is unambiguous. It does not explicitly contrast itself with any sibling, but none of the listed siblings (trim, convert, concat, etc.) perform audio addition, so confusion risk is low.

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?

"mode = 'replace' (new audio only) or 'mix' (blend with the original)" gives effective guidance for choosing between the two behaviors, which is the main decision point. However, there is no statement of when to use this tool versus alternatives, no prerequisites (e.g., URL accessibility or format support), and no exclusions.

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