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IntoDNS.ai DNS & Email Security Scanner

by ai.intodns
OverviewDiscussionsAdmin

Check mail server STARTTLS

check_smtp_tls
Read-onlyIdempotent

Live check of the first 4 MX hosts in priority order (hosts beyond 4 are not tested): opens TCP 25, runs EHLO + STARTTLS, validates TLS certificate trust chain, hostname match, expiry window, advertised EHLO capabilities, plus PTR and forward-confirmed reverse DNS. Read-only — connects and quits without sending mail. Returns per-MX TLS protocol version, certificate subject/issuer/SANs/validity/SHA-256 fingerprint, expiry days, and FCrDNS details. Use to verify inbound mail TLS posture; pair with check_mta_sts for the policy layer. May be slower (10-30s) due to live SMTP handshakes. Measured from the IntoDNS.ai server: a host that does not answer there has startTlsSupported null (not measured), not false; do not report that as missing STARTTLS. No auth.

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_smtp_tls"
  }
}

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

A4.5/5.0
Behavior5/5

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

Annotations cover the safety profile (readOnly, idempotent, non-destructive, open-world), and the description adds genuinely non-obvious behavior: live TCP 25 handshakes, 10-30s latency, connections quit without sending mail, measurement is from the IntoDNS.ai vantage point, and a non-responding host yields null rather than false. The null-vs-false warning is exactly the kind of interpretation guidance annotations cannot convey.

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?

The most decision-relevant constraint (first 4 MX, priority order, hosts beyond 4 untested) is front-loaded, and each subsequent sentence adds a distinct fact: operations performed, return shape, pairing guidance, latency, null semantics. Nothing repeats structured fields and nothing is padded.

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 no output schema, the description fully specifies the return payload (per-MX protocol version, cert subject/issuer/SANs/validity/SHA-256 fingerprint, expiry days, FCrDNS). It also discloses the measurement vantage point and latency, which are the two things most likely to cause an agent to misreport results.

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?

The single `domain` parameter is fully documented in the schema (domain only, no URL/path/port) at 100% coverage, so the schema carries the load. The description implies the domain drives MX lookup but adds no syntax, normalization, or edge-case detail beyond what the schema already states — baseline 3 is appropriate.

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 — a live STARTTLS/TLS check against the first 4 MX hosts in priority order — and enumerates exactly what is validated (cert trust chain, hostname match, expiry, EHLO capabilities, PTR/FCrDNS). It also distinguishes itself from the policy-layer sibling by naming check_mta_sts, so an agent can separate the two without opening either schema.

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?

Explicitly says 'Use to verify inbound mail TLS posture' and points to check_mta_sts for the complementary policy layer, plus a clear scope limit (hosts beyond 4 are not tested). It stops short of naming when to prefer adjacent siblings like check_tlsa_dane or check_fcrdns, which overlap on the DANE and reverse-DNS angles, so the routing guidance is strong but not exhaustive.

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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