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

TableJSON 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

TableJSON 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 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

A4.4/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds real behavioral context: 16 provider families are probed, a 15-name built-in list is used when no subdomain list is supplied, and caching exists. It stops short of describing pagination or output shape, but output schema exists.

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 core purpose and vulnerability class, then usage and pairing guidance. The parenthetical provider list is somewhat long but earns its place by conveying coverage breadth. No filler sentences.

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 read-only scanning tool with an output schema, the description covers purpose, trigger conditions, companion tooling, detected-provider scope, and the built-in-list fallback. Nothing an agent needs in order 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.

Parameters3/5

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

Schema description coverage is 100%, so all four parameters are documented in the schema itself; baseline 3 applies. The description reinforces the subdomains parameter by suggesting CT enumeration or brand-audit discovery as sources, but adds no syntax beyond what the schema provides.

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 precise verb+resource+outcome: 'Sweep subdomains for dangling CNAMEs pointing to deprovisioned cloud services that could be claimed by an attacker.' It names the vulnerability class explicitly and lists the provider families detected, so an agent can distinguish it from siblings like discover_subdomains or check_shadow_domains.

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 trigger ('Use when asked if subdomains are pointing to deprovisioned cloud services') and names the companion tool, discover_subdomains, plus the reason to pair ('widen the candidate set'), while clarifying that sibling returns only a CT sample. Routing is unambiguous.

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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