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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered, but the description adds nothing about behavior beyond the cost hint. It does not state that results are paginated across pages via the cursor, nor what a page contains, and the phrase "Comments on a YouTube video" reads ambiguously like a write action, which works against the read-only annotation.

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?

Two short sentences with no wasted words, and the credit cost is front-loaded alongside the purpose. However, the brevity comes at the cost of under-specification rather than efficiency, since key routing and pagination information is absent.

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 paginated read tool with a nearly identical sibling (youtube_comment_replies), an output-less schema, and no annotations explaining return shape, the description should at minimum clarify read-vs-write and pagination behavior. Neither is present, so an agent must infer the tool's role from its name and schema 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 coverage is 100%, with url, order (enum relevance/time) and cursor all documented in the schema, so the baseline of 3 applies. The description adds no meaning beyond the schema, not even noting that pagination requires reusing data.cursor.

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?

"Comments on a YouTube video" is a noun/verb phrase that does not clearly say whether the tool fetches existing comments or posts a new one; only the readOnlyHint resolves the ambiguity. It also does not distinguish itself from the sibling youtube_comment_replies, so an agent cannot route between the two from the description alone.

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 when-to-use guidance, no mention of the alternative youtube_comment_replies, and no indication of prerequisites such as a video having comments enabled. The only added sentence is a credit-cost note, which is not usage guidance.

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