Identify the channel behind the credential

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

The description goes well beyond the annotations by revealing a quota cost ('Costs 1 YouTube Data API quota unit'), a required scope ('needs the youtube.readonly scope'), and a conditional fallback behavior ('with only the analytics scope it reports the scopes it has instead'). These are important non-obvious traits that help an agent predict side effects and edge cases. No contradiction with annotations.

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?

The description is exactly two sentences. The first sentence front-loads the core purpose and output, while the second adds crucial context (entry point, quota, scope, fallback). Every clause earns its place; there is no fluff or redundancy.

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?

Given the tool's simplicity (0 params, no output schema), the description is complete: it explains the channel it targets, its role among siblings, expected return values (counts or scopes), and caveats (quota, scope requirements). The agent can confidently select and invoke this tool without additional documentation.

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 tool has zero parameters, so the description has no parameter semantics to clarify. Per the rubric, a 0-parameter tool gets a baseline of 4. The description adds no parameter-specific information, but none is needed.

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 clearly states the tool's function: 'Show which YouTube channel this server's OAuth credential owns, with its public subscriber, view, and video counts.' It uses a specific verb (Show) and resource (channel), and explicitly lists the output counts. It also distinguishes itself from siblings by noting 'every other tool reports on this channel and only this channel,' making its unique role as the channel-identifying entry point unmistakable.

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 description provides strong when-to-use guidance: 'This is the entry point' and 'start here to confirm you are looking at the right account.' It implies alternatives (the other tools that report on this channel) but does not explicitly state when not to use the tool or name specific alternatives for different purposes. The context is clear enough for an agent to know this is the first tool to call.

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