domain-security-mcp-server

MX Lookup

mx_lookup

Read-onlyIdempotent

Find a domain's MX records to see mail server priority and resolved IP addresses, helping audit email routing and security.

Instructions

Look up a domain's mail servers (MX records) with priority and the IPs they resolve to.

Args:

domain (string): the domain to query.
response_format ('markdown' | 'json'): output format (default 'markdown').

Returns: array of { exchange, priority, ips[] }.

Example: "What are the mail servers for github.com?" -> mx_lookup(domain="github.com").

Input Schema

TableJSON Schema

Name	Required	Description	Default
`domain`	Yes	Domain to query, e.g. 'example.com'.
`response_format`	No	Output format: 'markdown' for a human-readable summary (default) or 'json' for the full structured payload.	markdown

Output Schema

TableJSON Schema

Name	Required	Description	Default
`domain`	Yes
`records`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 schema fields changedv1.2.1Sep 14, 2026

changedInput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

removedInput schema / additionalProperties
```
Removed value: -false
```
addedInput schema / properties / domain / maxLength
```
Added value: +253
```

changedOutput schema / $schema

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

First observedv1.0.0Jun 8, 2026

TDQS

A3.8/5.0

Behavior4/5

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

The annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false. The description adds useful behavior beyond that: it converts MX lookups into a structured result of exchange, priority, and resolved ips[]. It does not mention external network dependency or failure modes, but for a simple read-only DNS lookup this is not a serious gap and there is no contradiction with the annotations.

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?

The description is compact and front-loaded with the purpose sentence, followed by concise Args, Returns, and Example sections. The Args list somewhat duplicates the schema, but the redundancy is minimal and the overall structure is easy for an agent to scan.

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 two-parameter tool with full schema coverage, an output schema, and read-only annotations, this description is complete: it explains the query target, the output format choices, the return shape, and provides a concrete example. Nothing essential to selecting or invoking the tool correctly 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 description coverage is 100%: both domain and response_format are documented in the schema. The description's Args section largely restates those schema definitions, and the example only reinforces the domain parameter without adding meaning beyond what the schema already provides.

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 opening sentence states a specific verb and resource: 'Look up a domain's mail servers (MX records) with priority and the IPs they resolve to.' This clearly identifies what the tool does and distinguishes it from the other DNS/email sibling tools by naming the exact record type and outputs, though it does not explicitly contrast it with siblings.

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?

The example 'What are the mail servers for github.com?' implies when the tool is appropriate, but the description gives no explicit when-to-use or when-not-to-use guidance, nor does it point to alternatives such as dns_lookup for general DNS record queries. The usage context is clear but left to inference.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.