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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds genuinely new context beyond the annotations: the credit cost (2 points per returned record) and the exact shape of returned records, which matters for budgeting calls.

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 tightly packed sentences with zero waste: the first front-loads what is returned, the second states the cost. Nothing redundant, nothing missing that belongs here.

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, listing the returned fields (author, text, likes, reply count, creator heart, timestamp) is exactly the right compensation, and the pricing note is a useful extra. Minor gaps remain around pagination/truncation behavior and how replies are nested, but the agent has enough to call it 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?

Schema description coverage is 100%, so url, sort_by, newer_than and max_comments are all documented in the schema itself. The description adds no extra parameter semantics (no note on period syntax for newer_than or on pagination relative to max_comments), so 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?

Specific verb (Get) plus a precisely scoped resource (comments and replies of a YouTube video), and it enumerates the returned fields. It does not, however, distinguish itself from siblings such as run_youtube_channel or run_youtube_shorts, so an agent must infer that this is the comments-specific tool.

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?

Usage is only implied: the agent can infer it should call this when it has a video URL and wants comment data. There is no explicit when-to-use or when-not-to-use guidance, and no mention of how it relates to run_youtube_search or run_youtube_shorts.

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