Mix audio tracks

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

The description goes beyond the basic annotations by explaining ducking behavior, the order of operations ('Per-track gain and start offsets are applied before the mix'), and that video from the primary input is passed through untouched. No contradiction with readOnly/destructive hints.

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 brief paragraphs, front-loaded with a clear purpose sentence. Every sentence contributes meaningful information with no filler.

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?

Core mixing behavior and important edge cases are covered. Remaining details like duration, encode options, and output path are documented in the schema, and an output schema exists, so the description is sufficient for selecting and invoking the tool.

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?

The description adds practical meaning to central parameters: explains 'duck', clarifies gain/start application order, and maps video passthrough to keep_video_from_voice. Schema covers many other fields well, so the description augments rather than repeats.

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 opens with a specific verb and resource: 'Mix background music or effects under a primary voice track.' It clearly distinguishes this from sibling tools like concat or overlay by detailing ducking and video passthrough.

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 conveys a clear use case—mixing music or effects under narration—and explains when ducking is useful. However, it does not explicitly mention alternative tools or state when not to use this tool.

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