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 two genuinely useful facts beyond the annotations: the target must be a public video, and the call costs 20 points — a cost signal that affects invocation decisions and appears nowhere in structured fields. It stops short of describing failure behavior on private/removed videos, keeping it off 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?

Front-loaded with the verb and key resource, which is good, but the same field list is repeated verbatim in Korean, doubling length without adding information for a given reader. The trailing point-cost tag is useful but the bilingual duplication is not fully earning its place.

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 single-param read-only lookup with no output schema, the description is close to sufficient: it names the returned fields, the accessibility constraint, and the cost. Nothing essential for correct invocation is missing, though a note on behavior for non-public videos would close the last gap.

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% and the schema already documents the accepted URL/ID formats, so the description correctly defers to it. The description adds no syntax or format detail beyond what the schema param description provides — the baseline 3 for a fully-covered single param.

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?

States a specific verb ('Look up metadata') and resource ('public YouTube video'), then enumerates the exact fields returned (title, channel, duration, views, likes, upload date, description, tags, chapters, thumbnails). This lets an agent distinguish it from siblings like youtube_subtitle, youtube_thumbnail, or download_youtube_video without opening a schema.

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?

The description scopes usage to 'public' videos, which implicitly tells the agent when it will and won't work, but it never names an alternative or states when to prefer crawl_youtube or youtube_subtitle instead. Usage is implied rather than routed.

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