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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so safety is covered. The description adds two things the annotations cannot: the return payload (video IDs, titles, channels, durations, view counts) and a cost/quota model ('Free on paid plans; Free plan: 10 a day, then 1 credit'), which is exactly the kind of budget constraint an agent needs before making repeated calls. The quota phrasing is slightly ambiguous about what happens after the 10th call.

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 purpose, then output shape, then cost, then the sibling handoff — a sensible order with no filler. The channel-form detail mildly duplicates the schema, costing a perfect score, but nothing is wasteful.

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?

There is no output schema, and the description compensates by enumerating the returned fields. Combined with read-only annotations, an open-world hint, and quota disclosure, an agent has everything needed to decide to call it and how to interpret results. Only the post-quota behavior is underspecified, which is minor.

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 100%, so the baseline is 3. The description restates the channel parameter's accepted forms (link or @handle), which the schema already documents as URL/channel ID/@handle, and says nothing about the limit parameter. No net meaning is added beyond the schema.

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 ('Search YouTube for videos') and immediately qualifies the scope with a second mode ('search within one channel by passing its link or @handle'). An agent can tell this is the discovery tool rather than a content-retrieval one, since the description explicitly hands off to get_transcript.

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 a clear next-step routing rule ('Use get_transcript on the videos you need') that links search to the sibling retrieval tool, plus the channel-narrowing option. It stops short of naming when not to use it (e.g. when the user already has a URL or playlist, where get_transcript or list_playlist_videos would be the entry point).

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