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Check one email address (syntax, mail servers, throwaway domain, role address)

email_address_check

Read-onlyIdempotent

Check ONE email address before you use it. Send the address; get a verdict (deliverable-domain, risky or invalid) and four checks: syntax, the domain's mail servers (public DNS), throwaway domain, and role address (info@, sales@). Signed and dated, so you can keep it as proof of what was checked. Free, no sign-up, 200 checks a day per caller. It never contacts a mail server, never asks whether the mailbox exists, never guesses or suggests an address, takes one address per call (no lists), and stores nothing. 'deliverable-domain' means the domain can receive mail, not that this inbox exists.

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": {
      "address": "<address>"
    },
    "name": "email_address_check"
  }
}

Input Schema

Name	Required	Description	Default
`address`	Yes	One bare email address such as name@example.com. No display name, no list.

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 13, 2026

TDQS

A4.3/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, non-destructive and open-world, yet the description still adds real context: a 200/day per-caller rate limit, no sign-up, nothing stored, no SMTP contact, and a signed/dated receipt for audit proof. It also pre-empts the biggest misinterpretation by defining 'deliverable-domain' as domain-level reachability rather than mailbox existence.

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?

Front-loaded with the action and the verdict shape, then the four checks, then constraints and rate limits. Dense but every sentence carries a distinct fact, and the string of explicit negatives is deliberate disambiguation rather than padding.

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?

There is no output schema, so the description compensates by enumerating the three verdict values and the four sub-checks returned. Combined with the rate limit and the definition of 'deliverable-domain', an agent has everything needed to call it and interpret the result.

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?

With one parameter at 100% schema coverage, the schema already documents the bare-address requirement and 254-char cap. The description restates the single-address constraint but adds no format or syntax detail beyond the schema, so baseline 3 applies.

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

Purpose5/5

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

States a specific verb and resource (check one email address) plus the exact checks performed: syntax, DNS mail servers, throwaway domain, role address. The 'ONE' emphasis and 'no lists' clause cleanly separate it from bulk or domain-level siblings like domain_health_check.

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?

'Check ONE email address before you use it' gives a clear trigger condition (pre-use validation) without naming a specific alternative tool. The negative scoping ('takes one address per call (no lists)') implicitly routes batch needs elsewhere, but no sibling is named explicitly.

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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