BlackVeil DNS & Email Security Scanner

check_subdomain_takeover

Read-onlyIdempotent

Sweep subdomains for dangling CNAMEs pointing to deprovisioned cloud services that could be claimed by an attacker (subdomain takeover vulnerabilities). Detects 16 provider families (AWS S3/CloudFront, Azure Front Door/CDN/Blob/App Service, GCP Cloud Storage, Heroku, GitHub Pages, Vercel, Firebase, Shopify, etc.). Use when asked if subdomains are pointing to deprovisioned cloud services. Pair with discover_subdomains to widen the candidate set — note that returns a CT sample, not a full inventory.

Input Schema

Name	Required	Description
`domain`	Yes	Domain to check (e.g., example.com).
`format`	No	Output verbosity. Auto-detected if omitted.
`subdomains`	No	Optional explicit subdomain list (full FQDNs or short labels). When provided (deduped, capped at 1000), this list is swept instead of the 15-name built-in. Source from Certificate-Transparency enumeration or brand-audit discovery.
`force_refresh`	No	Bypass cache and run a fresh check. Useful after DNS changes.

Output Schema

Name	Required	Description	Default
`score`	Yes
`passed`	Yes
`partial`	No
`category`	Yes
`findings`	Yes
`checkStatus`	No
`verdictWithheld`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 25, 2026
- addedInput schema / additionalProperties
```
Added value: +false
```
Changed1 schema field changedOct 5, 2026
- addedOutput schema / properties / verdictWithheld
```
Added value: +{
+  "type": "boolean"
+}
```
Changed2 schema fields changedAug 18, 2026
- addedOutput schema / properties / checkStatus
```
Added value: +{
+  "type": "string"
+}
```
- addedOutput schema / properties / partial
```
Added value: +{
+  "type": "boolean"
+}
```

Changed1 schema field changedJul 2, 2026

addedInput schema / properties / force_refresh

Added value: +{
+  "description": "Bypass cache and run a fresh check. Useful after DNS changes.",
+  "type": "boolean"
+}

Changed1 schema field changedMay 26, 2026

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "additionalProperties": {},
+  "properties": {
+    "category": {
+      "type": "string"
+    },
+    "findings": {
+      "items": {
+        "additionalProperties": {},
+        "properties": {},
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "passed": {
+      "type": "boolean"
+    },
+    "score": {
+      "type": "number"
+    }
+  },
+  "required": [
+    "category",
+    "score",
+    "passed",
+    "findings"
+  ],
+  "type": "object"
+}

Changed2 schema fields changedMay 24, 2026

changedInput schema / properties / domain / description

Previous value: -"Domain to check (e.g., example.com)"New value: +"Domain to check (e.g., example.com)."

addedInput schema / properties / subdomains

Added value: +{
+  "description": "Optional explicit subdomain list (full FQDNs or short labels). When provided (deduped, capped at 1000), this list is swept instead of the 15-name built-in. Source from Certificate-Transparency enumeration or brand-audit discovery.",
+  "items": {
+    "maxLength": 253,
+    "minLength": 1,
+    "type": "string"
+  },
+  "maxItems": 1000,
+  "type": "array"
+}

Changed2 schema fields changedMay 23, 2026

changedInput schema / properties / domain / description

Previous value: -"Domain to check (e.g., example.com)."New value: +"Domain to check (e.g., example.com)"

removedInput schema / properties / subdomains

Removed value: -{
-  "description": "Optional explicit subdomain list (full FQDNs or short labels). When provided (deduped, capped at 1000), this list is swept instead of the 15-name built-in. Source from Certificate-Transparency enumeration or brand-audit discovery.",
-  "items": {
-    "maxLength": 253,
-    "minLength": 1,
-    "type": "string"
-  },
-  "maxItems": 1000,
-  "type": "array"
-}

AddedMay 22, 2026

TDQS

A4.3/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent, non-destructive, open-world behavior, so the description need not restate safety. It adds real value by disclosing the default built-in 15-name sweep versus a user-supplied list, and the provider coverage scope. It stops short of stating rate-limit or timing expectations for a live DNS sweep.

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?

Front-loaded with the purpose and vulnerability class before the provider list and usage notes. Dense but every clause carries information; the provider enumeration is slightly long but useful for scope-setting.

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?

Output schema exists so return values needn't be explained, and annotations cover the safety profile. The description supplies the default-behavior context and the sibling caveat, leaving only minor gaps like runtime expectations for a live external sweep.

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%, so the baseline is 3. The description's note about subdomain sourcing echoes what the schema already documents for the subdomains parameter; it adds only marginal semantics (CT enumeration / brand-audit sourcing) beyond structured fields.

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 (sweep/check) and resource (subdomains), and precisely names the vulnerability class (dangling CNAMEs to deprovisioned cloud services claimable by an attacker). It enumerates 16 provider families, which distinguishes it sharply from siblings like check_subdomailing or discover_subdomains.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives an explicit triggering condition ('Use when asked if subdomains are pointing to deprovisioned cloud services') and an explicit pairing instruction with discover_subdomains, including the crucial caveat that discover_subdomains returns a CT sample rather than a full inventory. That is exactly the routing information an agent needs.

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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