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. The description adds one genuinely useful behavioral fact, the 20-point-per-call cost, but says nothing about return format, pagination, or rate limits beyond the cost note.

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?

It is short and front-loaded: the purpose sentence comes first, followed by the bilingual restatement and the cost marker. Nothing is wasteful, though the Korean translation duplicates the English sentence rather than adding information.

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 simple read-only listing tool with a complete input schema and annotation coverage, the description supplies what an agent needs, including the cost consideration. It is not required to explain return values since no output schema exists, but a brief note on result shape would have made it fully complete.

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 both the hashtag format (optional #) and the count range/default are already fully documented in the schema. The description adds no parameter detail beyond that, 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 description states a specific verb and resource ('List videos on a YouTube hashtag page'), which clearly scopes the tool to hashtag feeds rather than keyword search. It does not explicitly name the obvious sibling (youtube_search) to sharpen the boundary, so it stops short of a 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 implied by the resource scope — an agent can infer this is for hashtag-based browsing — but there is no explicit when-to-use, when-not-to-use, or reference to alternatives like youtube_search or youtube_playlist. It relies on inference.

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