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

Goes well beyond the readOnly/openWorld annotations: discloses that captionless videos return an empty segment list, private/removed videos return 404, bot-checked requests return 503 without charge and should be retried, and that successful calls cost $0.002 USDC via x402 with failures not billed. A rare case where a paid tool fully explains its error/cost semantics.

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?

A single dense paragraph that is front-loaded with what the tool returns, then error modes, then pricing. Every sentence carries real information (fallbacks, status codes, billing), though it is somewhat long.

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?

Even though an output schema exists, the description still frames the return shape and fully covers the error/retry/payment behavior for an x402-paid, open-world tool. Nothing needed to invoke it correctly or handle common failures 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?

Schema coverage is 100%, so both parameters are already documented, making baseline 3 appropriate. The description mentions 'available caption languages' and 'the chosen track,' which loosely connects to the lang parameter's behavior, but adds no syntax or format detail beyond the schema.

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 — 'Transcript (captions) of a public YouTube video from YouTube caption tracks' — and enumerates the returned fields (title, channel, length, timed segments, joined text). This is clearly a transcript extractor, distinct from siblings like social_youtube or social_youtube_comments, though it never explicitly names an alternative for routing.

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 conveys implied usage constraints (must be public, prefers human captions, lang fallback to first track) but never states when to reach for this tool over social_youtube or other siblings, nor any exclusions beyond 'public' videos. An agent can infer the use case but gets no explicit comparative guidance.

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