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

Annotations already cover read-only and open-world nature, but the description adds material context beyond them: the tool costs 1 credit on success, defaults to plain text, and offers timestamp/SRT/VTT variants. The "on success" qualifier usefully implies failed calls are not billed, though failure modes (no captions, private video) go unmentioned.

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, front-loaded with the verb and resource, followed by output options and then cost. Every clause carries information; no filler or repetition of 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?

For a single-required-parameter read tool with no output schema, the description covers return formats and cost well enough to invoke correctly. The remaining gap is error behavior — what an agent gets when no transcript or requested language is unavailable — which matters because "best available" language resolution is not explained.

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 the schema already documents url, lang, format, and timestamps thoroughly, including the enum meanings. The description adds little beyond restating the text/timestamps/SRT/VTT modes and omits mention of the json format and lang selection, so the 3 baseline 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?

States a specific verb and resource ("Get the full transcript (captions) of a YouTube video") plus the return variants. The name/title pair is unambiguous and clearly distinct from siblings get_video_metadata and list_videos, which deal with metadata and collections rather than caption text.

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 resource named — an agent can infer it should call this when it needs caption text rather than metadata. However, there is no explicit when-to-use or when-not-to-use framing, and neither sibling is named as an alternative (e.g., fall back to get_video_metadata when a video has no captions).

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