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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), and the description adds real behavior beyond that: public-videos-only scope, subtitles vs. automatic captions, translation support, and a 30-second timestamp cadence. It omits what happens on truncation via max_chars and any rate-limit behavior, keeping it out of the top tier.

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 return payload, then usage conditions, then a concrete example — efficient and scannable. Slightly loose in mixing output description and conditional guidance in the same breath, but nothing is padding.

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 enumerates returned fields, which is valuable. However, for a 5-parameter tool with 40% schema coverage it leaves the truncation semantics of max_chars (default 20000, cap 50000) and the start offset unexplained, which is a material gap for long videos.

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 only 40%, and the description only illuminates two of five parameters: it implies the video argument via the example and mentions lang for translation. start, max_chars, and timestamps are left entirely undocumented in both schema and description, and the 30-second timestamp claim is the only hint at the timestamps flag.

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 (returns) and resource (title, channel, duration, full transcript of a public YouTube video), plus caption source and timestamp cadence. No siblings exist, so no differentiation is needed, and the scope is unambiguous.

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?

The 'Use when:' line gives concrete triggering conditions (need to know what is said, summarize, quote) and an example invocation. There are no alternative tools to route against, so the absence of exclusions is not a defect.

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