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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, openWorldHint), so the description only needs to add context. It contributes the cost signal ('Free') and the sequencing constraint that this call should precede get_transcript, which is genuinely useful behavior information. It does not mention rate limits, quota consumption, or failure modes (e.g. unavailable/private 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?

Three short sentences: what it returns, its cost/position in a workflow, and the sibling to use instead. The return fields are front-loaded and every sentence carries distinct 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?

With no output schema, the description compensates by enumerating the returned fields, and it routes the agent to get_video_details for the fields it does not return. For a single-parameter read tool with strong annotations, nothing an agent needs to call it correctly is missing.

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?

There is a single parameter with 100% schema description coverage ('YouTube video ID or URL'), so the schema already carries the semantics. The description adds nothing about accepted ID/URL formats, so the 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?

The description names the exact return payload (title, channel, duration, caption languages) for a specific resource, which is more precise than the name alone. It also explicitly contrasts itself with get_video_details, so an agent can separate the two without opening either 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?

It states a concrete workflow use ('check which languages exist before asking for a transcript') and names the alternative plus the condition that selects it ('for view, like and comment counts or the publish time, use get_video_details'). Both when-to-use and when-not-to-use are covered explicitly.

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