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

Annotations already declare this a safe, open-world read (readOnlyHint=true, destructiveHint=false, openWorldHint=true), so the safety profile is covered. The description adds genuine behavioral context beyond that: it caps the result at the 15 newest uploads and enumerates the channel metadata fields returned, which tells the agent the shape and volume of the response. Pagination and rate-limit behavior remain unstated, so it stops short of 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 sentences, each earning its place: the trigger, the accepted inputs, then the disambiguation. The usage condition is front-loaded and there is no redundant 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?

There is no output schema, so the description must carry the return-value burden, and it does by enumerating the channel fields and the 15-upload cap. Combined with the explicit sibling routing, an agent has everything needed to select and invoke this tool correctly.

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?

There is a single parameter with 100% schema description coverage, so the baseline is 3. The description's "Accepts an @handle, channel URL, or UC... ID" merely restates what the schema already says and adds no format constraints, validation rules, or examples beyond it.

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 verb and resource, and goes further by naming what is returned: channel details (name, handle, description, subscribers) plus the 15 newest uploads. This is unambiguous and clearly separable from the other channel-related siblings.

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?

Opens with an explicit trigger condition ("when the user asks what a YouTube channel has posted recently") and then names two alternatives with the exact conditions that select them: list_channel_videos for full upload history, search_channel_videos for a topic inside one channel. Nothing 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.