SpamFixer Email Deliverability Check

Check email deliverability

check_email_deliverability

Read-onlyIdempotent

Check why emails from a domain might land in spam.

Looks up the domain's public DNS: SPF, DKIM (common selectors), DMARC, MX, and whether its mail servers are on major blocklists. Returns a 0-100 score and plain-English issues, worst first. Read-only: it changes nothing and sends no email. DKIM keys on custom selectors can't be found from outside, so "DKIM not found" is only a hint. Free email providers (gmail.com etc.) aren't checked.

Args: domain: The domain that sends the email, e.g. "joesplumbing.com". A website URL or an email address also works; the domain is taken from it.

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_email_deliverability"
  }
}

Input Schema

Name	Required	Description	Default
`domain`	Yes

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 28, 2026

TDQS

A4.7/5.0

Behavior5/5

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

Beyond the readOnly/idempotent annotations, the description discloses the mechanism (public DNS lookups plus blocklist checks), the output shape (0-100 score with plain-English issues worst first), and critical caveats such as false-negative DKIM results and skipped free providers. These limitations materially change how an agent should interpret the result.

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 purpose and result shape are front-loaded in the first paragraph, with caveats following. The 'Args:' block is slightly verbose in formatting but contains no wasted content, so the mild structure cost is the only deduction.

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 single-parameter read-only lookup with an output schema, everything needed is present: what is queried, what is returned, safety profile, and the two cases where results are unreliable. Nothing an agent needs in order to call it or interpret it is missing.

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

Parameters5/5

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

Schema description coverage is 0%, so the description carries the full burden, and it does: it explains the parameter is the sending domain and that a website URL or email address is also accepted with the domain extracted. That is exactly the input flexibility an agent could not infer from a bare 'string' schema.

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?

The description opens with a concrete verb and resource ('Check why emails from a domain might land in spam') and then enumerates exactly what is inspected: SPF, DKIM, DMARC, MX, and blocklists. An agent knows precisely what the tool does without opening the 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?

It states clear boundaries on when not to use it: free email providers like gmail.com aren't checked, and DKIM on custom selectors can't be found. There are no sibling tools to route to, so no alternatives are named, but the exclusion conditions are explicit.

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

All SpamFixer Email Deliverability Check tools Inspect

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