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BlackVeil DNS & Email Security Scanner

by com.blackveilsecurity
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discover_subdomains

Read-onlyIdempotent

Find subdomains via Certificate Transparency logs to reveal shadow IT and forgotten services. Returns a CT SAMPLE, not an asset inventory: counts are a lower bound, hosts without a logged certificate never appear, and a per-source coverage record states what was consulted. countBasis marks totalSubdomains as sample or a cut-recall floor; concreteSubdomains excludes wildcards.

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": "discover_subdomains"
  }
}

Input Schema

NameRequiredDescriptionDefault
domainYesDomain, e.g. example.com
formatNoOutput verbosity.
force_refreshNoBypass the cache.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changed
    • changedInput schema / properties / domain / description
      Previous value: -"Domain to check (e.g., example.com)"New value: +"Domain, e.g. example.com"
    • changedInput schema / properties / force_refresh / description
      Previous value: -"Bypass cache and run a fresh check. Useful after DNS changes."New value: +"Bypass the cache."
    • changedInput schema / properties / format / description
      Previous value: -"Output verbosity. Auto-detected if omitted."New value: +"Output verbosity."
  2. Changed1 schema field changed
    • addedInput schema / additionalProperties
      Added value: +false
  3. Changed1 schema field changed
    • addedInput schema / properties / force_refresh
      Added value: +{
+  "description": "Bypass cache and run a fresh check. Useful after DNS changes.",
+  "type": "boolean"
+}
  4. First observed

TDQS

A3.9/5.0
Behavior5/5

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

Annotations already declare readOnly/openWorld/idempotent/non-destructive, and the description goes well beyond them: it discloses that results are a CT sample, that counts are a lower bound, that hosts without logged certificates never appear, and that per-source `coverage` and `countBasis` markers qualify the data. This is exactly the kind of reliability context an agent needs before treating results as ground truth.

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?

Dense but front-loaded: the purpose lands in the first clause, followed by tightly packed caveats. Some field-level jargon (`countBasis`, `concreteSubdomains`) is carried in the description only because no output schema exists, so it earns its place, though the packing is heavy.

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 takes on the burden of explaining return semantics and does so well via the coverage/countBasis/concreteSubdomains notes. It never clarifies caching behavior tied to `force_refresh`, which is the main remaining gap.

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%, so the schema already documents `domain`, `format`, and `force_refresh`. The description adds no parameter-level detail (e.g., what the enum values change or when to bypass cache), so the baseline of 3 applies.

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?

States a specific verb and resource plus the mechanism ('Find subdomains via Certificate Transparency logs') and the underlying goal ('reveal shadow IT and forgotten services'). It does not explicitly distinguish the scope from sibling domain-discovery tools like discover_brand_domains, so it stops short of a 5.

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?

Use is implied by the goal statement ('reveal shadow IT and forgotten services'), but there is no explicit when-not guidance, no named alternative for full asset enumeration, and no stated prerequisites. The sample-vs-inventory caveat functions partly as usage framing but is framed as output behavior rather than tool selection guidance.

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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