Johto Data

Johto Data Email Domain DNS Check

email_domain_check

Read-only

MX, SPF presence and exact-domain DMARC policy diagnostics via DoH. Domain only, no mailbox addresses, SMTP or send. Not deliverability verification; SPF includes and organizational DMARC fallback not evaluated. Costs $0.0009 USDC per call via x402. Without payment, the call returns the x402 payment requirements; retry with an X-PAYMENT or PAYMENT-SIGNATURE header, or params._meta["x402/payment"].

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "domain": "<domain>"
    },
    "name": "email_domain_check"
  }
}

Input Schema

Name	Required	Description	Default
`domain`	Yes	Domain only, not an email address; ASCII/punycode

Schema Changelog

Changes observed during successful MCP inspections.

AddedNov 8, 2026

TDQS

A4.3/5.0

Behavior5/5

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

Beyond readOnlyHint/openWorldHint, it discloses that calls are metered at $0.0009 USDC via x402, that an unpaid call returns payment requirements rather than data, and exactly how to retry (X-PAYMENT / PAYMENT-SIGNATURE header or params._meta["x402/payment"]). That is precisely the operational detail annotations cannot convey and an agent needs to recover from a first failed call.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three tight, front-loaded statements: what it checks, what it is not, and how to pay. No filler, no repetition of the title, and the critical exclusions land before the payment mechanics.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a one-parameter read-only diagnostic with no output schema, the definition covers scope, non-goals, cost, the payment handshake, and the input format constraint. Nothing an agent needs to invoke it successfully or recover from a payment rejection is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% on a single parameter, and the description's 'Domain only, no mailbox addresses' plus the ASCII/punycode constraint largely restate what the schema already documents. The baseline of 3 applies since the description adds no new syntax, examples, or edge-case meaning beyond the structured field.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb set and resource scope: MX, SPF presence, and exact-domain DMARC policy diagnostics via DoH. The qualifiers ('exact-domain', 'SPF presence') implicitly carve out scope relative to the sibling dns_records tool, but that sibling is never named, so an agent must infer the distinction.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives clear when-to-use context ('Domain only, no mailbox addresses, SMTP or send') and explicit when-not-to-use warnings ('Not deliverability verification; SPF includes and organizational DMARC fallback not evaluated'), which prevents overreach. It stops short of naming an alternative tool (e.g., dns_records) for the excluded cases, so routing 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.

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