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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description adds real value beyond that: the publishedTime field is best-effort derived from a relative label, results are capped near 1,000 top or 7,000 newest comments, and calls cost credits. The pricing text is internally inconsistent ("at least 10 Nexscope credits" vs. "1 credit per request"), which muddies rather than clarifies the cost model.

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 useful content is front-loaded, but the tail is pasted pricing boilerplate that repeats the comment limits and cost twice ("YouTube Comments API View Pricing...", "Can only get 1k top comments and about 7k new comments. 1 credit per request") and ends with a disclaimer about example prices. Roughly half the text is redundant vendor copy.

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 carries the burden of describing returns, and it does list the returned fields plus the timestamp caveat and result caps. Cost behavior is mentioned but self-contradictory, leaving the one materially ambiguous area for an agent that must decide whether to re-request.

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 url, order, and continuationToken are already documented in structured fields. The description restates the order and continuation behavior at roughly the same level of detail without adding format or constraint information beyond the schema, so the baseline 3 applies.

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 opening sentence names a specific verb and resource (fetches comments and replies from a YouTube video) and enumerates the returned fields, so an agent knows exactly what it gets. It does not explicitly distinguish itself from the close sibling social_youtube_video_comment_replies, which limits it to a 4.

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 description explains that ordering can be top or newest and that continuationToken paginates, which implies usage but never states when to choose this tool over the sibling replies tool or when not to use it. The cost note gives a mild decision signal (repeated requests may purchase data again) but no explicit alternative routing.

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