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

With no annotations, the description carries the full burden and does substantial work: it discloses the non-SMTP methodology, the ≤50 batch cap, the three verdict tiers with reasons, and the cost/payment mechanism ($0.003 USDC per call via x402 on Base). It does not cover error behavior, rate limits, or what happens when an address is malformed, which keeps it short of 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?

A single dense paragraph that front-loads the calling modes, then the evidence returned, then the pricing caveat. The enumeration of checks is long but every item carries signal for an agent deciding whether to call it.

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 naming the returned fields (normalized form, MX records, typo suggestion, verdict with reasons). For a two-parameter, zero-required read-style tool, nothing an agent needs in order to call it correctly or interpret the result 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?

Schema description coverage is 100%, so both parameters are already documented, including the 'same price' note on emails. The description restates those facts but does add the either/or exclusivity implied by zero required parameters, which the schema leaves ambiguous. That modest addition lands at the baseline 3.

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 (validate an email address) and immediately enumerates the exact checks performed: RFC 5322 syntax, MX/A records, disposable, role account, free provider, typo suggestion, and verdict classes. It is clearly distinguishable from most siblings by domain, though it never differentiates itself from the plausibly overlapping domainaudit_email sibling.

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 explains the two calling modes (one address via email=, up to 50 via emails=) and notes 'No SMTP probing' as a scope exclusion, but gives no explicit when-to-use guidance or a named alternative such as domainaudit_email. Usage is implied rather than directed.

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