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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description adds a genuinely useful behavioral fact, the 20-point cost per call, but says nothing about pagination, rate limits, or behavior when a channel is not found.

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 core sentence is front-loaded and efficient, but the same content is then repeated verbatim in Korean, roughly doubling the length without adding information. The cost note is well placed but the duplication dilutes conciseness.

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?

With no output schema, the description correctly carries the burden of describing returns (name, handle, subscribers, description, and tab items). The main omission is guidance on which sibling to pick for adjacent YouTube tasks, but for calling this tool correctly it is largely complete.

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 coverage is 100%, so tab, count and channel are all documented in the schema with defaults and ranges. The description reinforces the meaning of the tab values and the returned fields but adds no format or syntax detail beyond the schema. Baseline 3 is appropriate.

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 (look up a YouTube channel) and enumerates what it returns (name, handle, subscribers, description) plus the tab listings. It is clear what the tool does, but it never names or distinguishes itself from near-neighbors like youtube_search, youtube_playlist, or crawl_youtube.

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?

There is no explicit when-to-use or when-not-to-use guidance. With siblings such as youtube_search, youtube_playlist and crawl_youtube in the same family, the agent must infer from the name alone which one applies, which is exactly the ambiguity the description should resolve.

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