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

Annotations already cover the safe-read profile (readOnlyHint, idempotentHint, non-destructive), so the description's main value-add is the billing model: charged per video, transcript billed separately, and transcripts only exist when captions are present. That is meaningful operational context beyond the annotations. Missing rate-limit or quota details keeps 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?

Effectively two sentences, front-loaded with the returned fields and followed by the transcript and billing caveat. There is no filler, and each clause conveys usable 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 read-only fetch tool with complete schema coverage and no output schema, the description does well by enumerating the returned fields and explaining transcript availability. Minor gaps remain around error behavior when no captions exist or language fallback, but the essentials are covered.

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%, with each of the three parameters documented and defaults stated. The description only reinforces the optional transcript behavior and says nothing about the language parameter, so it adds little beyond the schema. 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 pair: 'Public stats for one YouTube video', and enumerates exactly what the stats include. The phrase 'one YouTube video' also separates it from the sibling youtube_search, which searches videos rather than fetching a single video's metrics.

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 makes the use case clear: fetch stats for a known video, optionally with transcript. It does not explicitly name youtube_search as the alternative or say when-not to use it, so it stops just short of full routing guidance.

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