domain-security-mcp-server

DNSBL Blacklist Check

blacklist_check

Read-onlyIdempotent

Check if an IPv4 address or domain is listed on open-access email DNS blocklists, returning listing status, reason, and query errors.

Instructions

Check whether an IPv4 address (or a domain's A records) appears on email DNS blocklists (DNSBLs). Only open-access lists are queried (SpamCop, UCEPROTECT-1, DroneBL, s5h); Spamhaus and Barracuda refuse public-resolver queries and are excluded.

Args:

query (string): an IPv4 address or a domain.
response_format ('markdown' | 'json'): output format (default 'markdown').

Returns: { ips[], listedCount, checked, results[{ip, hits[{list, listed, reason, error}]}], note }. A list that did not answer carries an error and is not counted as clean.

Example: "Is 203.0.113.5 blacklisted?" -> blacklist_check(query="203.0.113.5").

Input Schema

TableJSON Schema

Name	Required	Description	Default
`query`	Yes	An IPv4 address or a domain to check against DNSBLs.
`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
`ips`	Yes
`note`	Yes
`query`	Yes
`checked`	Yes
`results`	Yes
`listedCount`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed6 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 / query / 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"

addedOutput schema / properties / results / items / properties / hits / items / properties / error
```
Added value: +{
+  "type": [
+    "string",
+    "null"
+  ]
+}
```

changedOutput schema / properties / results / items / properties / hits / items / required

Previous value: -[
-  "list",
-  "zone",
-  "listed",
-  "reason"
-]New value: +[
+  "list",
+  "zone",
+  "listed",
+  "reason",
+  "error"
+]

First observedv1.0.0Jun 8, 2026

TDQS

A4.4/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior, so the description need not repeat safety. It adds valuable behavioral context: only open-access lists are queried, non-answering lists carry an error and are not counted as clean, and the return structure is described. This goes beyond annotations and gives the agent a clear expectation of edge cases.

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 organized into a clear opening statement, Args, Returns, and an Example. It is thorough but not redundant; every sentence adds information. The only slight redundancy is the return structure being partially explained in both the description and the schema, but it is not excessive.

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 tool with two parameters and a structured output, the description is complete: it defines the purpose, scope of lists, input types, output format, and return payload, including error handling for unresponsive lists. The example clarifies invocation. Nothing an agent needs to call it correctly is missing.

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

Parameters4/5

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

Schema coverage is 100% with descriptions for both query and response_format. The description reinforces this by clarifying query accepts IPv4 or domain, and response_format has a default and two enum values. It also adds an example usage that demonstrates parameter invocation, exceeding the baseline set by the 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 states a specific action ('Check whether...') on a specific resource ('IPv4 address or a domain's A records') against DNSBLs, and distinguishes it by naming the exact lists included and excluded. This clearly differentiates it from sibling tools like spf_check or dmarc_check, which target other email authentication mechanisms.

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 description makes the intended use clear: checking DNSBL status. It also provides an explicit exclusion of Spamhaus and Barracuda due to public-resolver refusal, giving the agent context on limitations. However, it does not explicitly name alternative sibling tools for other email checks, though the purpose is distinct enough that this is a minor gap.

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