Agent Tools

email_check

Validate email address syntax, check MX mail servers, detect disposable or temporary domains, identify role addresses (info@, sales@) and free providers. Returns deliverable_guess. For signup forms, lead lists and CRM cleanup. No SMTP probe, no data stored. Price $0.001 USDC per call via x402. Example output: {"email":"jane@acme.com","valid_syntax":true,"domain":"acme.com","mx_records":["10 mx1.acme.com."],"has_mail_server":true,"disposable":false,"role_account":false,"free_provider":false,"deliverable_guess":"likely"}

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": {
      "email": "<email>"
    },
    "name": "email_check"
  }
}

Input Schema

Name	Required	Description	Default
`email`	Yes	Email address to validate

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 22, 2026

TDQS

A3.8/5.0

Behavior4/5

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 no data storage, no SMTP probing (so results are a guess, not a verification), a per-call price of $0.001 USDC via x402, and the exact return fields via an example output. It stops short of stating rate limits, latency, or how deliverable_guess values other than 'likely' are classified.

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

Conciseness4/5

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

Content is front-loaded: capabilities first, then when to use, then constraints and cost, then return shape. The example output is long but earns its place because no output schema exists. Minor waste in restating field names already covered by the capability list.

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

Completeness4/5

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

For a one-parameter read-style tool with no annotations and no output schema, the definition covers capabilities, limits, cost, and exact return shape, which is nearly everything an agent needs. The remaining gap is relative positioning against the batch/full siblings, which is left implicit.

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

Parameters4/5

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

There is a single required parameter with 100% schema description coverage, so the schema already defines it. The description reinforces that the input is a raw address whose syntax, domain, and MX are each evaluated, and the example output clarifies what the address is decomposed into, adding light meaning beyond the schema.

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 gives specific verbs and resources: validate syntax, check MX records, detect disposable domains, identify role accounts and free providers, and return deliverable_guess. It is clearly distinguishable from a generic lookup, but it never names the sibling variants (email_check_batch, email_check_full) even though 'No SMTP probe' implies email_check_full does more.

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

Usage Guidelines3/5

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

It supplies usage contexts ('For signup forms, lead lists and CRM cleanup') and a negative scope statement ('No SMTP probe'), which implies a deeper sibling exists. However, there is no explicit when-to-use-this-vs-alternative routing, so an agent must infer that batch or full variants exist for other cases.

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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