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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered. The description adds real value with the credit cost ("2 credits"), which annotations cannot express, but omits behavior an agent would want: whether URLs expire, whether downloads count against rate limits, or whether geo/age restrictions can cause failure.

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?

A single short sentence with the core capability front-loaded and the cost trailing as a parenthetical — no filler. The phrase "plus every format" is slightly vague but costs only a few words.

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?

For a one-parameter read-only tool with no output schema, the description does convey the shape of the return (MP4 stream URLs, quality tiers). It still leaves the agent guessing about URL lifetime, response structure, and failure modes, which matters for a download-oriented 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?

There is one parameter with 100% schema description coverage ("YouTube video URL."), so the schema already does the work. The description adds no format hints such as whether short links, playlist links, or video IDs are accepted, so the baseline 3 applies.

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?

The description names the specific resource produced — direct MP4 stream URLs for a YouTube video — and lists the format coverage (360p with audio plus every format), which separates it from metadata siblings like youtube_video or youtube_transcript. It stops short of a verb-first statement and never explicitly says 'download' or names a sibling it replaces.

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?

There is no explicit guidance on when to choose this over youtube_video, youtube_transcript, or youtube_playlist, and no stated preconditions. The only implicit signal is that the output is stream URLs, leaving the agent to infer the use case.

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