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by ai.intodns
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Check MTA-STS

check_mta_sts
Read-onlyIdempotent

Read-only check of MTA-STS: TXT record at _mta-sts. plus the HTTPS policy file at mta-sts./.well-known/mta-sts.txt. Returns parsed policy (mode: enforce/testing/none, mx allowlist, max_age), TLS certificate validity for the policy host, and consistency warnings between DNS and HTTPS. Use to verify enforced TLS for inbound mail; pair with check_smtp_tls for live STARTTLS validation. No auth, DNS + HTTPS GET only.

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": "check_mta_sts"
  }
}

Input Schema

NameRequiredDescriptionDefault
domainYesDomain name only, e.g. example.com (no URL, path, or port)

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

A4.7/5.0
Behavior5/5

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

Annotations already declare readOnly/idempotent/openWorld, but the description adds real context: no authentication needed, DNS + HTTPS GET only, and the exact return payload (mode, mx allowlist, max_age, TLS cert validity, DNS/HTTPS consistency warnings). That tells the agent what network effects and outputs to expect beyond the safety hints.

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 dense sentences ordered purpose → return shape → usage pairing, with no filler. Every clause carries an actionable detail.

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?

With one parameter, full schema coverage, no output schema, and rich annotations, the description supplies the missing piece: what the check actually returns and how it relates to sibling tools. Nothing needed to invoke it correctly is absent.

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% and the single 'domain' parameter is fully documented in the schema, including the 'no URL, path, or port' constraint. The description adds no parameter-level detail beyond what the schema already provides, so the baseline of 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 action and resource ('Read-only check of MTA-STS') and enumerates exactly what is inspected: the _mta-sts TXT record and the HTTPS policy file. It is clearly distinguishable from neighboring tools like check_smtp_tls or check_bimi.

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

Usage Guidelines5/5

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

Names the use case ('verify enforced TLS for inbound mail') and the complementary sibling ('pair with check_smtp_tls for live STARTTLS validation'), giving the agent a routing rule rather than leaving it to infer.

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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