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

Annotations only declare readOnlyHint and openWorldHint, so the description carries real added weight: it discloses the 1-hour link expiry, the base-fee-plus-per-10MB billing model, the 30-point per-call charge, and the public-video restriction. It omits failure behavior (geo-blocked, private, age-gated videos) and any rate limits, which keeps it short of 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 core action and scope in the first clause, then billing and the youtube_formats pointer, which is a sensible priority order. The full Korean restatement duplicates every fact already given in English, which is defensible for the audience but adds bulk.

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 correctly compensates by describing the return value (a download link valid for 1 hour) and the cost model, so the agent knows what it gets and what it pays. The only remaining gap is error/failure semantics for unavailable videos, which is minor for a 5-parameter, mostly self-documenting tool.

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, quality, start, end, and codec with examples and defaults. The description only restates 'chosen quality (up to 4K)' and 'optionally only a time range' at a high level, adding no syntax or edge-case detail beyond the schema (e.g., what happens if start exceeds end). 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?

States a specific verb+resource (download a public YouTube video) plus the output format (MP4), the quality ceiling (up to 4K), the optional time-range trimming, and the returned artifact (1-hour download link). An agent can distinguish this from youtube_audio_download, video_to_mp3, and youtube_formats without opening any 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?

Explicitly routes the agent through youtube_formats first to inspect sizes and estimated costs, which is a concrete usage prerequisite rather than a vague hint. It also implies the scope limit (public videos only) and that billing scales with file size, but it never states when-not to use it (e.g., versus the audio-only or subtitle siblings).

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