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

Annotations already indicate readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds valuable context beyond this: multiple channels are accepted in one call, each channel counts as one request against the plan, missing public emails return found=false rather than an error, and contact-block emails are resolved. This meaningfully discloses operational behavior.

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 compact and front-loaded with the core purpose, followed by input format details, behavior notes, and billing implications. Every sentence provides actionable information without redundancy or filler.

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?

The description is largely complete for a one-parameter read-only lookup: it covers input variants, multi-channel behavior, quota cost, and the not-an-error case of missing emails. A minor gap is the exact return payload structure beyond the found flag, since no output schema is provided, but the description still gives enough to call the tool correctly.

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 input schema provides only 'channels' as an array of strings with 0% parameter description coverage. The description fully compensates by enumerating accepted value formats: channel links, '/channel/UC...' links, '@handle', and channel_id. It also clarifies cardinality semantics by stating each list item counts as one plan request.

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 opens with a specific verb and resource: 'Encontra o e-mail de contato de canais do YouTube.' This clearly states what the tool does and distinguishes it from the unrelated sibling tools. It also narrows the purpose to contact emails, including those in the contact block, not just the description.

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 gives clear context for when to use the tool: whenever you need a YouTube channel's public contact email. It also explains acceptable input formats and batching behavior. It does not explicitly name alternatives or exclusions, but the sibling tools are unrelated, so this is not a significant gap.

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