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

Annotations cover the safety profile (readOnlyHint, openWorldHint), and the description adds genuinely useful behavior beyond them: the return value is a download link valid for exactly 1 hour, and pricing is a base fee plus per-10MB plus 20 points per call. It omits failure behavior (private/age-restricted videos), maximum size, and whether delivery is synchronous.

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?

Purpose is front-loaded and the cost/expiry facts earn their place, but the entire text is duplicated in Korean and English, roughly doubling token cost with zero new information for the agent. The trailing point-cost tag is useful but bolted on.

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 single-input, no-output-schema tool the description covers the essentials: input source, output form, link lifetime, and cost model. Missing pieces are edge-case behavior (private videos, size limits, async vs sync delivery) that a paid download tool would ideally state.

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 all five parameters are already documented in the schema and the baseline is 3. The description restates format options and mentions the optional time range but says nothing about the bitrate parameter or its MP3-only constraint, so it adds no meaning 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 gives a specific verb and resource ('Download only the audio of a public YouTube video as MP3, M4A or Opus') and the word 'only' implicitly separates it from the sibling download_youtube_video. It never names a sibling or contrasts itself explicitly, so an agent must still infer the boundary against download_youtube_video and video_to_mp3.

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 'public YouTube video' qualifier implies a usable scope (public sources, audio-only) and the time-range option implies partial extraction. However, there is no explicit when-to-use/when-not guidance and no routing advice versus download_youtube_video or video_to_mp3, which are the most likely confusions.

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