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

No annotations, so the description carries the full burden, and it discloses key behavioral facts: the $0.01 USDC per-call cost, that it returns x402 payment requirements, and that the caller's wallet must execute the payment. That payment/auth flow is significant context. It omits rate limits and what a failed MX check implies, keeping it below 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-loads purpose, then output contents, then pricing/payment, then a concrete example — a logical progression with little filler. Slightly dense but each sentence (including the payment note) 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?

An output schema exists, so return-value explanation is not required, and the description instead fills the more important gap of the x402 payment flow. The one remaining gap is that it never says what the tool returns once payment succeeds, but the output schema and payment note largely cover the agent's needs.

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 0% for the single required 'domain' parameter, so the description must compensate. The worked example email_pattern(domain="acme.com") does clarify that the value is a bare domain rather than a URL or email address, which is useful, but nothing is said about subdomains or edge-case formats.

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?

Names a specific verb+resource: generating likely corporate email address patterns for a domain plus MX verification. The parenthetical examples (first.last@, first@, flast@) make the output concrete. It does not explicitly distinguish itself from close siblings like deliverability or lookup_lead, which also touch email/lead data, so it stops short of a 5.

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 implies the use case (lead enrichment / Apollo-style verification) but never states when to choose this over deliverability, contact_page, or lookup_lead, nor any prerequisites or exclusions. Usage is left to inference from the phrasing.

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