Subdomain API MCP

An MCP server that provides access to the Subdomain API, allowing AI agents to query for known subdomains of a given domain name. It returns up to 10,000 subdomains, sorted by most recently seen, including counts and distinct totals.

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Endpoint and access

No sign-in to connect and list tools. Individual tools may still need a vendor account, credentials, or permissions; check the documented prerequisites.

Vendor evidenceStreamable HTTPNo sign-inEndpoint checked 2026-11-07Operated by Fili Wiese

MCP endpoint (Streamable HTTP)

https://api.subdomain.app/mcp

Vendor documentation

What its tools do

2 tools, grouped by the hints the server advertises. Hints are self-declared, not verified behavior.

2 of 2 have a description · 2 of 2 declare behavior hints · 2 of 2 with parameters document them all

Checks and signals

Each line is separate evidence, not a trust score.

Passed Endpoint answered the live check · Nov 7, 2026, 8:59 AM UTC
Passed Official MCP Registry namespace is tied to subdomain.app · Nov 7, 2026, 6:23 AM UTC
Passed Endpoint is on the registry namespace domain · Nov 7, 2026, 6:23 AM UTC
Availability 1 of 1 checks passed in 30 days

What you can do with it

Find known subdomains of a domain
Count distinct subdomains for a domain
Retrieve passive DNS data for security analysis

Source and maintenance

Vendor evidenceRegistry 1.0.1

mcp-registry: app.subdomain/subdomains@1.0.1 Project website

Protocol and capabilities

Server: subdomain-app 1.0.0
MCP protocol negotiated in check: 2025-11-25
Tools: 2 advertised
Resources: Not advertised
Resource templates: Not advertised
Prompts: Not advertised

Server-advertised capabilities

{
  "tools": {
    "listChanged": true
  }
}

Tools

2 advertised

find_subdomains — Find subdomains

Advertised by the server during the last successful anonymous check.

Advertised read-onlyOpen-world

List known subdomains (hostnames) of a root domain. Data is passive (not active scanning): results are historic observations and may include subdomains that no longer resolve or are no longer live. Results are a point-in-time snapshot that changes over time as new subdomains are observed — re-query rather than caching the result. Use for attack-surface mapping, security recon, asset inventory, or SEO host discovery. Hostnames are returned most-recently-seen first. The response always reports `total` (full distinct count known) and a `truncated` flag, so you can tell when more exist beyond `limit`.

find_subdomains input schema

{
  "type": "object",
  "$schema": "http://json-schema.org/draft-07/schema#",
  "required": [
    "domain"
  ],
  "properties": {
    "limit": {
      "type": "integer",
      "default": 200,
      "maximum": 1000,
      "minimum": 1,
      "description": "Max subdomains to return (1-1000, default 200). `total` always reports the full count regardless of this cap."
    },
    "domain": {
      "type": "string",
      "description": "Root (registrable) domain as a bare hostname, e.g. \"example.com\". No scheme, path, port, or leading \"www.\" — these are stripped."
    }
  }
}

find_subdomains output schema

{
  "type": "object",
  "$schema": "http://json-schema.org/draft-07/schema#",
  "required": [
    "domain",
    "total",
    "returned",
    "truncated",
    "subdomains"
  ],
  "properties": {
    "total": {
      "type": "integer",
      "maximum": 9007199254740991,
      "minimum": -9007199254740991,
      "description": "Total distinct subdomains known."
    },
    "domain": {
      "type": "string"
    },
    "returned": {
      "type": "integer",
      "maximum": 9007199254740991,
      "minimum": -9007199254740991,
      "description": "Number in `subdomains`."
    },
    "truncated": {
      "type": "boolean",
      "description": "True if more exist beyond `limit`."
    },
    "subdomains": {
      "type": "array",
      "items": {
        "type": "string"
      }
    }
  },
  "additionalProperties": false
}

find_subdomains annotations

{
  "readOnlyHint": true,
  "openWorldHint": true,
  "idempotentHint": true
}

count_subdomains — Count subdomains

Advertised by the server during the last successful anonymous check.

Advertised read-onlyOpen-world

Return only the total number of distinct subdomains known for a domain — no list. Cheap and low-token. Use when the user asks "how many subdomains" or you only need the size of the attack surface. Count includes historic subdomains that may no longer be live. It is a point-in-time figure that changes over time, so treat it as current-as-of-query, not a fixed value.

count_subdomains input schema

{
  "type": "object",
  "$schema": "http://json-schema.org/draft-07/schema#",
  "required": [
    "domain"
  ],
  "properties": {
    "domain": {
      "type": "string",
      "description": "Root (registrable) domain as a bare hostname, e.g. \"example.com\". No scheme, path, port, or leading \"www.\" — these are stripped."
    }
  }
}

count_subdomains output schema

{
  "type": "object",
  "$schema": "http://json-schema.org/draft-07/schema#",
  "required": [
    "domain",
    "total"
  ],
  "properties": {
    "total": {
      "type": "integer",
      "maximum": 9007199254740991,
      "minimum": -9007199254740991,
      "description": "Total distinct subdomains known."
    },
    "domain": {
      "type": "string"
    }
  },
  "additionalProperties": false
}

count_subdomains annotations

{
  "readOnlyHint": true,
  "openWorldHint": true,
  "idempotentHint": true
}

Prompts

Not advertised

No prompt definitions available.

Resources

Not advertised

No resource definitions available.

30-day availability

Aggregated from read-only remote checks; this is not a tool-execution or security guarantee.

Successful checks: 1 of 1 (100%)
Average latency: 994 ms
95th percentile latency: 994 ms

Maintenance history

Public check and source-refresh events. Editorial and ownership records remain private.

Nov 7, 2026, 8:59 AM UTC · probe · passed · 994 ms · metadata changed · 2 tool(s)

Connect from your client

Each snippet registers the same endpoint; pick the client you use.

This server is operated by the named third party. Listing and endpoint checks are not an endorsement or a security audit. Review the operator's permissions, terms, and data handling before connecting. How listings are checked and corrected.

Claude Code

Run this once in a terminal. It registers the remote server. Use --scope project to write .mcp.json for the repo.

Claude Code configuration

claude mcp add --transport http subdomain-api-mcp https://api.subdomain.app/mcp

Codex

Run this once. Codex stores MCP servers in ~/.codex/config.toml (or .codex/config.toml in a trusted project).

Codex configuration

codex mcp add subdomain-api-mcp --url https://api.subdomain.app/mcp

Cursor

Merge this server into .cursor/mcp.json in your project, then enable subdomain-api-mcp in your MCP settings.

Cursor configuration

{
  "mcpServers": {
    "subdomain-api-mcp": {
      "url": "https://api.subdomain.app/mcp"
    }
  }
}

Cline

Merge this into cline_mcp_settings.json (Cline → MCP Servers → Configure).

Cline configuration

{
  "mcpServers": {
    "subdomain-api-mcp": {
      "type": "streamableHttp",
      "url": "https://api.subdomain.app/mcp",
      "disabled": false
    }
  }
}

VS Code

Merge this server into .vscode/mcp.json. Use MCP: List Servers to start subdomain-api-mcp and inspect its tools.

VS Code configuration

{
  "servers": {
    "subdomain-api-mcp": {
      "type": "http",
      "url": "https://api.subdomain.app/mcp"
    }
  }
}

Gemini CLI

Run this once. It writes .gemini/settings.json in the current project; pass --scope user for ~/.gemini/settings.json.

Gemini CLI configuration

gemini mcp add --transport http subdomain-api-mcp https://api.subdomain.app/mcp

Claude Desktop

Open Claude Settings > Connectors > Add custom connector, enter this server URL and enable it for the conversation. This is a manual remote-connector handoff, not a desktop JSON configuration.

Claude Desktop configuration

https://api.subdomain.app/mcp

Windsurf

Merge this into ~/.codeium/windsurf/mcp_config.json, then refresh MCP in Cascade. Windsurf remote servers use serverUrl, not url.

Windsurf configuration

{
  "mcpServers": {
    "subdomain-api-mcp": {
      "serverUrl": "https://api.subdomain.app/mcp"
    }
  }
}

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