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

Annotations only declare readOnlyHint and openWorldHint; the description goes well beyond them by disclosing the exact billing model (6 credits per started minute, with a 10-minute worked example), the hard 45-minute ceiling, and the failure-charge policy ("a video that cannot be transcribed, or any failure, costs nothing"). This is exactly the kind of cost/limit context an agent needs before committing a call.

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 tight sentences, front-loaded with purpose then cost then failure policy. No filler and nothing repeated from the title.

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 state the return format ("as text"), and it covers cost, length limits, and failure behavior for a paid external call. Minor gap: it does not mention latency, whether long videos are rejected upfront, or how the transcript is formatted (timestamps vs plain prose), which would help an agent set expectations.

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%, so both url and idempotency_key are already fully documented in the schema. The description adds only the implicit constraint that the video must be public, matching the schema's wording; it says nothing about retry/idempotency semantics beyond what the schema covers, so 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?

Specific verb ("Return the transcript") plus specific resource ("one public YouTube video") plus output form ("as text"). Easily distinguished from siblings like scrape, search, or extract_contacts, which have nothing to do with YouTube transcription.

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 rather than stated: the agent can infer this is the tool for transcribing a YouTube URL, and the 45-minute cap implicitly describes when the tool will not work. However, no alternatives are named and there is no explicit when-to-use/when-not framing.

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