# Subdomain API (remote · api.subdomain.app)

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

- Trust score: 69/100 (medium)
- Change this week: +4
- Registry status: active
- Liveness: live
- Owner verified: no
- Last scored: 2026-08-03

## Components

- remote · `api.subdomain.app`: 69/100 (this document), [markdown](https://verifymcp.io/servers/app-subdomain-subdomains/api.md), [page](https://verifymcp.io/servers/app-subdomain-subdomains/api)

## Channel facts

- Endpoint: `https://api.subdomain.app/mcp`
- Transports: `streamable-http`
- Auth: `none`
- Version: `1.0.1`

## Trust breakdown

How this component scores in each security and reliability category. Every signal is checked automatically against the live server, and we only credit what we can confirm. Scores are 0–100 per category. Scoring method: https://verifymcp.io/docs/scoring (what has changed: https://verifymcp.io/docs/scoring/changelog)

Scored 2026-08-03.

- **Endpoint Security**: 60/100
  - The endpoint's TLS certificate is valid, in date, and uses a strong key.
  - Authorisation not fully verified: no authorisation is required to call this server, and 2 tool(s) never declared a destructiveHint. The MCP spec treats an absent hint as destructive by default, so we cannot call this surface safe.
  - HTTPS is enforced; there's no plaintext access path.
  - HSTS check failed: the Strict-Transport-Security header is absent.
  - DNSSEC is configured correctly; the domain's records validate against the full chain to the root.
- **Transport & Reachability**: 100/100
  - Verified streamable-http transport via a live MCP handshake.
- **Schema Quality & AI Usability**: 79/100
  - AI-judged instruction clarity (excellent).
  - Context-footprint check failed: tool/resource definitions use about 344 tokens (~172/item across 2 items; 2 tools + 0 resources), over budget; trim descriptions and params.
  - Usage-examples check failed: none of the tools include examples.
- **Stability & Change Management**: 27/100
  - Stability observed for 8 of 30 days with no destabilising changes; credit accrues until the full window elapses.
- **Tool Coverage**: 100/100
  - 100% of tools have a non-trivial description (not blank, and not just the tool's name).
  - 100% of tool parameters carry a description.
  - Structured output schemas are declared (100% of tools); any adoption earns full credit.
- **Capabilities**: 100/100
  - Implements a supported MCP spec version (2025-11-25); the latest is 2026-07-28.

## Install

### Claude

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

### Codex

```toml
[mcp_servers.app-subdomain-subdomains]
url = "https://api.subdomain.app/mcp"
```

### opencode

```json
{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "app-subdomain-subdomains": {
      "type": "remote",
      "url": "https://api.subdomain.app/mcp",
      "enabled": true
    }
  }
}
```

### OpenClaw

```bash
openclaw mcp add app-subdomain-subdomains --url https://api.subdomain.app/mcp --transport streamable-http
```

### Hermes

```yaml
mcp_servers:
  app-subdomain-subdomains:
    url: "https://api.subdomain.app/mcp"
```

### Other

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

The mcpServers block is a cross-client convention. Remote transports vary, so check your client's docs.

## Changelog

Every change recorded for this component, newest first. Days that predate change tracking, or that we cannot explain, say so: "we were watching and nothing happened" and "we were not watching" are different claims.

### 2026-08-03 (score 69, +1)

No change was recorded against any check on this day. Stability & Change Management went from 23 to 27. That category is still filling its 30-day observation window: 7 days of observed history at the previous scan, 8 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-08-01 (score 68, +1)

No change was recorded against any check on this day. Stability & Change Management went from 17 to 20. That category is still filling its 30-day observation window: 5 days of observed history at the previous scan, 6 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-07-31 (score 67, 0)

- [functional] We updated how we score, so this day's move reflects our rubric, not a change to the server

### 2026-07-30 (score 67, 0)

- [functional] We updated how we score, so this day's move reflects our rubric, not a change to the server

### 2026-07-29 (score 67, +1)

No change was recorded against any check on this day. Stability & Change Management went from 7 to 10. That category is still filling its 30-day observation window: 2 days of observed history at the previous scan, 3 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-07-28 (score 66, +1)

No change was recorded against any check on this day. Stability & Change Management went from 3 to 7. That category is still filling its 30-day observation window: 1 days of observed history at the previous scan, 2 at this one. The score rises as the window fills, whether or not the server changes.

### 2026-07-27 (score 65, 0)

- [functional] We updated how we score, so this day's move reflects our rubric, not a change to the server

### 2026-07-26 (score 65)

First indexed and scored.

## MCP tools (2)

### `find_subdomains` (~212 tokens)

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`.

Input parameters:

- `domain` (string, required): Root (registrable) domain as a bare hostname, e.g. "example.com". No scheme, path, port, or leading "www." — these are stripped.
- `limit` (integer): Max subdomains to return (1-1000, default 200). `total` always reports the full count regardless of this cap.

Output parameters:

- `domain` (string)
- `returned` (integer): Number in `subdomains`.
- `subdomains` (array)
- `total` (integer): Total distinct subdomains known.
- `truncated` (boolean): True if more exist beyond `limit`.

### `count_subdomains` (~132 tokens)

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.

Input parameters:

- `domain` (string, required): Root (registrable) domain as a bare hostname, e.g. "example.com". No scheme, path, port, or leading "www." — these are stripped.

Output parameters:

- `domain` (string)
- `total` (integer): Total distinct subdomains known.

## Diagnostics

Captured diagnostic sections: TLS, DNSSEC, Authorisation, Transports. The full working is on the page: https://verifymcp.io/servers/app-subdomain-subdomains/api#diagnostics

## Score history

- 2026-08-03: 69
- 2026-08-02: 68
- 2026-08-01: 68
- 2026-07-31: 67
- 2026-07-30: 67
- 2026-07-29: 67
- 2026-07-28: 66
- 2026-07-27: 65
- 2026-07-26: 65

## Links

- Remote endpoint: https://api.subdomain.app/mcp
- Website: https://subdomain.app/
- Changelog RSS feed: https://verifymcp.io/servers/app-subdomain-subdomains/api/changelog.xml
- Changelog JSON feed: https://verifymcp.io/servers/app-subdomain-subdomains/api/changelog.json
- HTML version of this page: https://verifymcp.io/servers/app-subdomain-subdomains/api