# Subdomain API

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

- name: app.subdomain/subdomains
- version: 1.0.1
- connection class: R0 (autonomous)
- trust: 75/100 flags: no-repository
- quality: 85/100 (good)
- owner: not claimed
- descriptor: https://api.protogrid.dev/v1/servers/app.subdomain%2Fsubdomains
- tools: https://api.protogrid.dev/v1/servers/app.subdomain%2Fsubdomains/tools

**An agent can connect right now, no human step.** Remote endpoint, no authentication, reachable on the last probe.

## Connection (mcpServers)

```json
{
  "mcpServers": {
    "subdomains": {
      "type": "http",
      "url": "https://api.subdomain.app/mcp"
    }
  }
}
```


## Trust

- hygiene: 80
- liveness: 98
- freshness: 65
- provenance: 55
- drivers: +dns-namespace +website +reachable +uptime-96% ~updated-117d-ago -no-repository
- Derived from observable signals (official registry feed and our own credential-free probes); no code audit performed.

## Quality 85/100 (good)

### protocol: 75 (weight 25)

- warn `protocol.modern`: newest supported version is 2025-11-25; 2026-07-28 not supported, older versions are deprecated until 2027-07-28
- n/a `protocol.stateless`: only applies to 2026-07-28 servers
- pass `protocol.transport`: streamable HTTP
- n/a `protocol.list_ttl`: only applies to 2026-07-28 servers

### authorization: n/a (weight 15)

- n/a `auth.prm`, `auth.as_metadata`, `auth.cimd`: no remote uses OAuth
- n/a `auth.secret_in_url`: no templated URL

### tool hygiene: 86 (weight 30)

- pass `tools.descriptions`: every tool has a description
- pass `tools.description_length`: descriptions are concise
- pass `tools.schemas`: every tool has an object input schema
- pass `tools.annotations`: 2 of 2 tools declare readOnlyHint or destructiveHint
- fail `tools.directory_hints`: no tool declares all four of readOnlyHint, destructiveHint, idempotentHint and openWorldHint; missing: find_subdomains (destructiveHint); count_subdomains (destructiveHint)
- pass `tools.token_cost`: about 472 tokens to load every tool
- pass `tools.api_dump`: tools are not a one-to-one API dump

### stability: 100 (weight 15)

- pass `stability.changes`: no tool changes in 30 days
- pass `stability.rug_pull`: no tool changed its meaning under the same name

### dependencies: n/a (weight 15)

- n/a `deps.known_vulns`, `deps.mcp_sdk_version`, `deps.resolvable`: no npm or PyPI package

- tools: 2, about 472 tokens to load them all
- tool set hash: bf2594d14555e49833d76c859be2d571
- badge: [![protogrid quality](https://protogrid.dev/badge/app.subdomain/subdomains.svg)](https://protogrid.dev/servers/app.subdomain/subdomains)
- Checks run on what our credential-free, read-only probes observe; tools are never called and no code audit is performed.

### Tool changes

_No tool definition changes recorded._

## Remotes

- https://api.subdomain.app/mcp (streamable-http, auth none, reachable true, uptime30d 0.95652175)

## Packages

_none_

## Tools (2)

- `count_subdomains`: 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.
- `find_subdomains`: 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`.