Crypto, web, finance and app data tools

Subdomain Finder

subdomain_finder

Subdomains of a domain found in public Certificate Transparency logs (crt.sh), with first certificate and current validity date. Use for attack-surface mapping, asset inventory or competitor research.

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": "subdomain_finder"
  }
}

Input Schema

Name	Required	Description	Default
`limit`	No
`domain`	Yes

Output Schema

Name	Required	Description	Default
`result`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

AddedOct 22, 2026

TDQS

B3.3/5.0

Behavior3/5

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

No annotations exist, so the description carries the burden; it usefully discloses the upstream source (crt.sh) and that results include first-certificate and current-validity dates. It says nothing about result caps, rate limits, or possible coverage gaps in CT data, which matter for a read-only lookup.

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 tight sentences: what the tool returns first, then when to use it. Nothing is wasted and the core capability is front-loaded.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness3/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return-value detail is not required, and the source disclosure helps. However, with zero annotation coverage and an undocumented `limit` parameter, the description does not fully equip an agent to invoke the tool correctly.

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

Parameters2/5

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

Schema coverage is 0%, so the description must compensate. It implies the `domain` input but never explains the `limit` parameter (default 200, presumably a max-results cap), leaving a real gap for an agent that wants to control output size.

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 resource (subdomains) and the exact data source (public Certificate Transparency logs / crt.sh), plus what's returned. It does not explicitly differentiate itself from near-neighbours like dns_lookup, ssl_certificate or domain_whois, so it falls 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 for attack-surface mapping, asset inventory or competitor research' gives positive use contexts, but there is no when-not guidance and no mention of the sibling tools (dns_lookup, ssl_certificate, domain_whois) an agent should weigh before choosing this one.

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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