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

Annotations already declare readOnly/openWorld/non-destructive, so the safety profile is covered. The description goes further by disclosing the response shape (segments with startMs/endMs/snippet/startTimeText plus availableTranscripts[] with language, type and selected flags) and the asr-vs-human-authored fallback behavior — useful context since there is no output schema.

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?

Front-loaded with the core purpose and return structure before the use-case list. It is a single dense paragraph whose sentences mostly earn their place, though the use-case enumeration runs 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?

With no output schema, the description compensates by explaining the transcript segment fields and the availableTranscripts listing. Together with a fully documented parameter schema and annotation-covered safety profile, an agent has everything needed to call and interpret this tool.

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 all three parameters (v, type, languageCode) are already documented in the schema; the description's parameter notes (languageCode examples, type=asr, default track behavior) largely restate that. Baseline 3 is appropriate when the schema does the heavy lifting.

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 YouTube Video Transcript... timed transcript (subtitles) of a YouTube video by its 11-character videoId'), immediately distinguishing it from the sibling video/channel/search endpoints. An agent can tell exactly what it returns without opening the 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?

Gives concrete usage contexts (RAG/LLM pipelines, summaries, chapter outlines, archives, translation/accessibility, catalog analysis) and a concrete routing hint ('pair with the YouTube Channel endpoint to enumerate videos, then fetch transcripts'). It lacks an explicit 'don't use this when...' contrast against siblings like getYoutubeVideo, so it falls short of a 5.

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