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dns

by com.blackveilsecurity

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
NameRequiredDescriptionDefault
domainYesDomain to check (e.g., example.com).
formatNoOutput verbosity. Auto-detected if omitted.
subdomainsNoOptional 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_refreshNoBypass cache and run a fresh check. Useful after DNS changes.

Output Schema

TableJSON Schema
NameRequiredDescriptionDefault
scoreYes
passedYes
partialNo
categoryYes
findingsYes
checkStatusNo

TDQS

A4.5/5.0
Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false. The description adds value by explaining the sweeping mechanism (CNAMEs, 16 providers), the built-in 15-name list, caching behavior (force_refresh), and parameter constraints. No contradictions with annotations.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Two sentences plus a concise usage note. Every sentence is purposeful: purpose, detection scope, usage context, and companion tool. No filler or repetition.

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?

Given the tool's complexity (4 parameters, 100% schema coverage, output schema present, full annotations), the description is complete. It explains the built-in subdomain list, parameter customization, caching, and pairing with discover_subdomains. No critical gaps.

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%, baseline 3. The description adds meaningful context for the 'subdomains' parameter (explicit list, source, capping, dedup) and 'force_refresh' (bypass cache). The 'domain' and 'format' parameters are not enhanced beyond the schema, but the overall addition is solid.

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 clearly specifies the action ('sweep subdomains'), the vulnerability ('dangling CNAMEs pointing to deprovisioned cloud services'), and the scope ('subdomain takeover'). It enumerates 16 provider families, distinguishing it from sibling check_* tools that focus on other security aspects.

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?

Provides explicit usage context: 'Use when asked if subdomains are pointing to deprovisioned cloud services.' Also advises pairing with discover_subdomains and notes that discover_subdomains returns a CT sample, not a full inventory. The description lacks an explicit 'when not to use' but the guidance is clear enough.

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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TDQS

A3.6/5.0
Disambiguation4/5

Most tools have clearly distinct purposes, with detailed descriptions that help differentiate overlapping areas (e.g., check_dane vs check_dane_https). However, there are sets of similar tools (brand audit, OSINT, polling) that could cause confusion if descriptions are not carefully read.

Naming Consistency3/5

The naming is mostly readable but inconsistent: many check_* tools follow a verb_noun pattern, but there are also noun_verb names (scan_domain, cymru_asn), bare verbs (generate), and varied patterns for async operations (discover_brand_domains_start vs discover_brand_domains).

Tool Count2/5

With 80 tools, the server feels overstuffed. It covers multiple domains (DNS, email, brand, OSINT, M365) that could benefit from separation. The high number includes many polling/status tools that add overhead.

Completeness3/5

The server covers core DNS and email security checks thoroughly, including many edge cases (e.g., BIMI, MTA-STS, subdomain takeover). However, there are gaps like lack of direct DNS record management and some OSINT tools are restricted to operator deployment, leaving agents with dead ends.

Resources