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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered; the description adds genuinely new behavior beyond that: the language fallback ('otherwise the default track') and the cost ('Costs 1 credit'). It stops short of describing pagination or transcript length handling, which would push it higher.

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 with the core purpose front-loaded, then output shape, then fallback and cost. Barely any waste, though the leading 'Video transcript.' fragment mildly restates the title before the more informative sentence.

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 does well to sketch the return format and cost, but it leaves cache_max_age unexplained and gives no hint about permission requirements or transcript availability failures. Adequate for a simple read tool, but there are remaining gaps an agent must guess at.

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 67%, and the description only enriches the language parameter by explaining the fallback-to-default behavior. The url parameter and cache_max_age are left entirely to the schema, and cache_max_age has no description in either place, so the description does not fully compensate for the coverage gap.

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 a specific verb and resource ('Full transcript for a YouTube video') and even states the return shape ('one text block plus timed cues'). This clearly distinguishes it from non-transcript YouTube siblings like youtube_video or youtube_videoComments, though it does not explicitly contrast with sibling transcript tools on other platforms.

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 implied by the platform-specific name and the phrase 'Full transcript for a YouTube video', but there is no explicit when-to-use versus alternatives (e.g., youtube_video for metadata) or when-not guidance. The language fallback note adds some operational context but not selection guidance.

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