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

Annotations already declare readOnlyHint/idempotentHint/openWorldHint and non-destructive, so safety is covered. The description adds genuinely new behavioral information: the return is SRT cue-by-cue and language falls back to the video's original when omitted. It stays silent on the AI-transcription fallback and plan limits, keeping it short of a 5.

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 action and return format, and no filler. Slight redundancy with the schema on the language default keeps it from a perfect score.

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 correctly carries the burden of describing the SRT return shape, which it does. The only gap is the forceAiTranscription/plan-limit behavior, which the schema parenthetically covers, so the definition is largely sufficient to call correctly.

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 all three parameters are already documented in the schema. The description's language note ('when omitted, the original language is preferred') largely restates the schema's 'Empty: the original language of the video', and forceAiTranscription is untouched, so it adds little beyond baseline.

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 ('Returns the transcript of one YouTube video') plus the exact output format (SRT with one timestamp per cue). This clearly separates it from siblings like get_video_info or search_videos, which do not return transcripts.

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?

'for reading what was said' implies a reading/consumption use case but gives no explicit when-to-use vs. when-not guidance and never names an alternative sibling (e.g. use get_video_info for metadata rather than transcript). Usage must be inferred from the purpose statement.

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