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

Beyond the readOnlyHint/openWorldHint annotations, the description adds the genuinely useful qualifier 'This is a metered live-data request,' warning agents of cost and freshness implications—valuable behavioral context an agent cannot infer from the annotations. The phrase 'exact publication data when available' hints at nullable/conditional returns for incomplete videos. It stops short of discussing rate limits, authentication, or error cases for invalid/deleted IDs, but given that annotations already signal a safe, read-only, open-world surface, the incremental disclosure is meaningful, pushing it above the minimum.

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 description front-loads a strong, verb-first sentence that captures the tool's essence, then lists the specific return fields, and closes with the operational warning. Every sentence earns its place—no filler, no repetition of the tool name or obvious parameters, and the paragraph break separates the definition from the warning. It's tight without being sparse.

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 only one well-constrained parameter, comprehensive annotations, and a present output schema, the description doesn't need to detail the return structure and reasonably keeps that to a short list. The metered/live warning covers the key operational caveat for a data-retrieval tool. The only minor gaps (region restrictions, handling of deleted videos, rate limits) are edge cases that would be nice-to-have but aren't essential for correct invocation.

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 0%, so the description carries the full explanatory burden, but with a single `video_id` parameter constrained by the YouTube ID regex pattern, the risk of misuse is low. The description's mention of 'a YouTube video ID' confirms the parameter's purpose in natural language. Since the parameter name plus the regex pattern already leave minimal ambiguity, the description's light touch suffices to reach a 4.

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 opens with a specific verb and resource: 'Fetch fresh metadata and engagement for a YouTube video ID.' It then enumerates concrete return dimensions (views, likes, comments, duration, tags, categories, channel identity) that clearly scope the tool to single-video metadata. This distinguishes it from siblings like get_youtube_video_transcript, get_youtube_channel, and search_youtube without being confused with them.

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 intended use—retrieving metadata for one YouTube video by ID—is implied by the verb 'Fetch' and the parameter name, and the metered-live-data note hints agents should call sparingly. However, there's no explicit routing to alternatives such as 'for transcripts, use get_youtube_video_transcript' or 'for channel data, see get_youtube_channel,' which the sibling list suggests would be valuable. No prerequisites, ordering constraints, or degradation conditions are stated; an explicit 'use this when' statement is absent.

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