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

Goes well beyond the readOnly/openWorld annotations: discloses the data source (caption track in the HLS playlist), the coverage limit (only transcript X exposes to logged-out callers), the empty-result behavior for uncaptioned posts, and the 1-credit cost with the no-charge caveat.

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?

Four short sentences, front-loaded with purpose and return shape, then source, then the empty-result/cost caveat. No filler and no repetition of the name.

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 usefully describes the return format, source, and billing edge case. It falls short only on the undocumented cache_max_age parameter and on any hint about the language-selection behavior the schema exposes.

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?

The description says nothing about any of the three parameters. The schema documents url and language, but cache_max_age has no description at all (67% coverage), and the description does not compensate for that gap or clarify accepted id formats.

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 ('Post transcript / captions for a video post on X') and defines the return shape ('one text block plus timed cues'), which cleanly separates it from twitter_tweet and twitter_userTweets metadata siblings.

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 — fetch this when you need captions for a video post — and the note that captionless posts return empty tells the agent when the tool will yield nothing. But it never names an alternative (e.g. twitter_tweet for non-video posts) or states prerequisites, so explicit routing is missing.

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