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

Beyond the annotations (destructiveHint=true, idempotentHint=false), the description discloses that rendering happens at publish time via the existing publisher, that no pre-rendered preview is returned, that original video duration is preserved, and that the change propagates to scheduled videos. These are non-obvious behavioral traits an agent must know before invoking a destructive edit.

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 purpose is front-loaded in a one-line summary, followed by scoping and warning sentences that each add information. Slight redundancy between the title line and the first body sentence, but overall tight for the amount of behavior disclosed.

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 destructive mutation tool with no output schema, the description adequately explains lifecycle behavior (publish-time render, scheduled-video impact) but leaves most of the 10-parameter surface undocumented, so an agent cannot confidently set volume, fade, loop, or start-time options from the definition alone.

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% across 10 parameters, so the description carries the full burden, yet it only indirectly covers 'mode' (mixing vs. replacement) and constrains audioUrl to a hosted library file. Eight parameters (fadeIn, loopAudio, trackName, audioVolume, audioStartTime, originalVolume, videoStartTime) get no semantic explanation anywhere.

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 states a concrete verb and resource ('Attach background audio to a video', 'Configure audio mixing or replacement on an unpublished video'), which is specific enough to separate it from generateMusic, generateVideo, or adjustTone. It clarifies that this edits an existing video rather than creating one, but never names a sibling tool directly.

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 gives real preconditions: the video must be unpublished, the audio must already be a hosted file in the user's own media library, and scheduled videos will pick up the change so the agent should confirm first. It stops short of naming alternative tools for related needs (e.g., generating music or editing an already-published video).

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