Ballast - Cold Email

Check domain

check_domain

Read-only

Inspect DNS and deliverability health of any domain without adding it. Performs a live, read-only diagnostic check on any domain name (MX, SPF, DKIM, DMARC records, blacklist status, and domain age) with actionable DNS fix instructions. Results are cached for 10 minutes. Nothing is saved to the workspace.

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_domain"
  }
}

Input Schema

Name	Required	Description	Default
`domain`	Yes	Domain to grade, e.g. yourdomain.com. URLs and email addresses are accepted.
`selector`	No	Optional custom DKIM selector to check in addition to the common ones.

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 21, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already cover read-only, non-destructive and open-world, but the description adds real value beyond them: the live network call, a 10-minute result cache, the explicit no-persistence guarantee, and an enumeration of what is checked (MX, SPF, DKIM, DMARC, blacklist, domain age). It does not mention rate limits, auth requirements, or how failures surface, which keeps it off a 5.

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 sentences, each carrying distinct load: scope/sibling differentiation, what is checked plus the live-and-cached behavior, and the persistence guarantee. Front-loaded and free of repetition.

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?

With no output schema, the description does well to promise "actionable DNS fix instructions" and to name the record types examined, giving the agent a sense of the return. It still leaves the shape of results (per-record verdicts, an overall grade, pass/fail granularity) unstated, which for a diagnostic tool would be the final useful addition.

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%, with both domain (including the useful note that URLs and emails are accepted) and selector fully documented in the schema. The description's "in addition to the common ones" only loosely echoes the selector parameter and adds no format or behavior detail beyond the schema, so the 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 ("Inspect DNS and deliverability health of any domain") and immediately scopes it against the sibling write path with "without adding it." An agent can distinguish this from add_domain and list_domains without opening any 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?

The phrase "without adding it" and "Nothing is saved to the workspace" clearly frame this as the non-persisting pre-check alternative to add_domain, and "any domain" signals no prerequisite setup. It stops short of an explicit "use this before add_domain" directive, so the routing is strongly implied rather than stated.

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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