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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, open-world). The description adds genuine extra context: it works with both creator-uploaded and auto-generated captions, and translate_to consumes extra credits that scale with transcript length.

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-loads the core action, then layers input formats, return shapes, and the cost caveat. Information-dense with almost no filler, though the format enumeration is slightly long for a single sentence.

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 an output schema present, return values need not be detailed, yet the description still usefully sketches format shapes and flag costs. Inputs, defaults, cost implications, and caption-source caveats are all covered — an agent has everything needed to invoke it 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 description coverage is 0%, so the description must carry the load, and it largely does — it explains accepted `video` formats and enumerates `format` values (timestamped default, text, srt, vtt, json) with their shapes. It omits any explanation of the `language` parameter, leaving one of four params undocumented.

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 ('Fetch') and resource ('transcript/captions of a YouTube video') clearly. None of the siblings (get_channel_videos, search_youtube, etc.) produce transcripts, so the tool is unambiguously distinguishable without opening a 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 explicit input-format guidance (watch URL, youtu.be, Shorts, bare 11-char id) and a conditional rule for translate_to ('omit unless asked'). No alternatives are named, but the sibling set has no overlapping transcript tool, so the missing exclusions matter little.

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