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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=true), so the bar is lower. The description adds genuine value beyond them: it restricts scope to PUBLIC videos, enumerates the response fields, and discloses a per-call cost ('호출당 30포인트'). It does not mention pagination limits or the reply-cap behavior, keeping it from a 5.

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 purpose is front-loaded in the first clause and the whole thing is three short segments. The Korean sentence restates the English one and the cost tag is appended, which is mild redundancy, but for a Korean-market toolset the bilingual phrasing is defensible rather than wasteful.

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 return-value burden and does so by listing the fields each comment includes plus the optional replies. All four parameters are covered by the schema and safety is covered by annotations. What remains thin is pagination/ordering behavior across large comment sets, which is not addressed.

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 the schema already documents url, sort, count and replies with defaults and ranges. The description only echoes the sort choices ('top or newest') and the optional replies, adding no syntax or format detail beyond the schema. Baseline 3 is correct.

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 gives a specific verb and resource: 'List comments of a public YouTube video', and even enumerates the returned fields (author, text, likes, pinned/hearted flags). The 'comments' resource is inherently distinct from all ~20 sibling youtube_* tools (search, metadata, channel, playlist, subtitle), so an agent can route to it correctly. It stops short of naming a sibling to avoid, so it lands at 4 rather than 5.

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 'public YouTube video' qualifier hints at the access constraint and the sort options are stated, but there is no explicit when-to-use/when-not guidance and no alternative named (e.g. youtube_metadata for video info, youtube_search for discovery). The purpose is self-evident enough that an agent can infer the trigger, which is the definition of a 3.

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