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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds genuinely non-structural context: the ¥0.2 per-call price, success-only billing, and automatic refund on failure or empty results — a real decision input for an agent. It does not cover pagination depth or rate limits, keeping it at 4.

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?

Four short sentences, front-loaded with purpose, then return fields, then usage, then billing. Every sentence carries distinct information — no restatement of the tool name and no 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?

For a two-parameter read tool with no output schema, the description is nearly self-sufficient: it lists return fields, states the prerequisite, and discloses the billing model. The only gap is whether results are paginated or capped per call, which an agent might need for large threads.

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% for the two parameters, so comment_id and _token are already documented. The description adds only the provenance hint that the comment ID must come from a main-comment fetch, which is useful but modest. Baseline 3 applies when the schema does the heavy lifting.

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 description states a specific verb and resource ("获取知乎评论的子评论") and immediately enumerates the returned fields (正文、点赞数、回复者信息、时间), so an agent knows exactly what it gets. The prerequisite "需先拿到主评论ID" implicitly separates it from the sibling zhihu_post_comments tool that produces those IDs.

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?

It gives an explicit use case ("追踪评论区的二次讨论与争议点") and a hard prerequisite (must already have the main comment ID), which routes the agent correctly when it has a comment_id vs. when it needs to fetch comments first. It does not name an alternative tool explicitly, so it falls just short of a 5.

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