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

With no annotations, the description carries the burden and does disclose key behaviors: the mailbox itself is not probed, and the call costs $0.001 in USDC on Base. It does not cover failure modes or response format, but the core limitations and pricing are transparent.

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?

Two sentences plus a pricing note; front-loaded with the action and scope, then limitations and cost. Every sentence earns its place.

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?

Core behavior and cost are covered, but there is no output schema and no mention of response shape or what happens without a payment parameter. It also doesn't clarify selection relative to email_verify, leaving moderate gaps for an autonomous agent.

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?

Both parameters are fully described in the schema (100% coverage), so the description adds little beyond schema. It only reinforces 'ONE' email address, which is already in the schema's email description. Baseline 3 is appropriate.

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 states a specific verb ('Check') and resource ('ONE email address'), and enumerates the checks performed: shape, live MX records, disposable domain, role account. It does not explicitly differentiate from the sibling 'email_verify', so full sibling distinction is missing.

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?

It gives clear context ('before sending to it') but no explicit alternatives or exclusions. With a closely named sibling 'email_verify' present, the agent is not told when to choose this tool over that one, leaving usage guidance implied rather than explicit.

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