# Subdomain API

> Use this tool when you need to identify potential security vulnerabilities or map out a domain's infrastructure by finding known subdomains of a given domain. It solves problems related to cybersecurity, network mapping, and domain research by providing a list or count of subdomains, including historic entries. The Subdomain API takes a domain as input and outputs a list or count of subdomains, making it useful for penetration testing, vulnerability assessment, and domain analysis.

Canonical page: https://skillsregistry.net/skills/app-subdomain-subdomains  
JSON: https://api.skillsregistry.net/v1/skills/app-subdomain-subdomains

## Description

Find known subdomains of a domain. Passive data; may include historic entries. List or count.

## Trust

- **Trust score (0–1):** 0.70
- **Verification tier:** unverified

## Facts

- **Version:** 1.0.0
- **Skill type:** atomic
- **Execution layer:** mcp-remote
- **Runtime environment:** api
- **Category:** api-integration
- **Updated:** 2026-09-26

## Source

- **Source listing:** [MCP Registry](https://registry.modelcontextprotocol.io/v0/servers/app.subdomain%2Fsubdomains)

## Use it

MCP endpoint published by the skill: `https://api.subdomain.app/mcp`

Resolve this record through the SkillsRegistry MCP server (no auth, read-only):

```
claude mcp add --transport http --scope user skillsregistry https://api.skillsregistry.net/mcp
```

```json
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "get_skill",
    "arguments": {
      "slug": "app-subdomain-subdomains"
    }
  }
}
```

REST: `GET https://api.skillsregistry.net/v1/skills/app-subdomain-subdomains` · pull for local use: `GET https://api.skillsregistry.net/v1/skills/app-subdomain-subdomains/pull`

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SkillsRegistry indexes agent skills from public registries and GitHub. Skills we have analysed are scanned with Circle-IR and scored on six dimensions; each listing states its scan coverage. More: https://skillsregistry.net/llms.txt