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 operational context beyond that: it reads the user's real connected channel directly, requires no input, and should be invoked immediately without gathering context from the creator. It does not cover latency, rate limits, or failure modes, which keeps it below a 5.

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 and output, then routing, then the no-input directive. Most sentences earn their place, but the closing clause ("not for context, not for a link, not for a title you could look up") is emphatic repetition that could be tightened.

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, so the description carries the return-value burden and does so: ranked prioritized list, funnel stage (packaging/retention/audience fit), and per-video cost. Combined with the no-input and immediate-call guidance, nothing needed to invoke it correctly is missing.

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?

Zero parameters, so the baseline is 4. The description reinforces this with "Needs no input: it reads their real connected YouTube channel directly," which tells the agent not to fabricate or solicit arguments.

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 (Diagnose) and resource (the signed-in user's YouTube channel), then specifies the output shape: a ranked, prioritized per-video worklist with funnel stage and cost. It explicitly distinguishes itself from the sibling audit_channel (channel-level context vs per-video worklist), so an agent can route correctly without opening either 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 an explicit trigger ("call it when the user asks what to fix or improve on their channel") and an explicit alternative with its own condition ("for what the channel is about... call audit_channel instead"). It also states the negative case for inputs: never ask the creator anything first.

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