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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety and external-dependency context is covered. The description adds genuinely new behavioral information by disclosing the 1-credit cost and that it is charged only on success. However, it says nothing about failure modes, quota or rate limits, or restrictions for private/region-locked videos.

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?

Two short sentences, front-loaded with the returned fields and ending with the cost caveat. No filler, though the field enumeration is a long comma list that could have been tightened.

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?

There is no output schema, but the description compensates by listing every returned field, which is exactly what an agent needs to decide whether to call it. Cost behavior plus the fully documented parameter makes this complete for a one-parameter read 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 coverage is 100% and the single url parameter is fully documented in the schema, including the accepted URL forms and 11-character id alternative. The description adds no meaning beyond that, so the baseline of 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 opens with a specific verb and resource ("Get ... of a YouTube video") and enumerates exactly which metadata fields come back, so an agent knows what it will receive. It doesn't explicitly contrast itself with the sibling get_transcript, and the mention of "available caption languages" slightly blurs the boundary with that tool.

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 only implied: fetch metadata for a given video URL. There is no statement of when to prefer this over get_transcript, nor any precondition such as the video being public or the URL being valid.

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