Subdomain API
REMOTE · API.SUBDOMAIN.APP · SCANNED SEP 22
Find known subdomains of a domain. Passive data; may include historic entries. List or count.
Available components
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. How we score → Why this is hard to score →
Endpoint Security60
- The endpoint's TLS certificate is valid, in date, and uses a strong key. View diagnostics → Pass
- 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. See how to fix → View diagnostics → Unverified
- HTTPS is enforced; there's no plaintext access path. View diagnostics → Pass
- HSTS check failed: the Strict-Transport-Security header is absent. See how to fix → View diagnostics → Fail
- DNSSEC is configured correctly; the domain's records validate against the full chain to the root. View diagnostics → Pass
Transport & Reachability100
- Verified streamable-http transport via a live MCP handshake. View diagnostics → Pass
Schema Quality & AI Usability82
- AI-judged instruction clarity (excellent).Pass
- 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. See how to fix → Fail
- Usage-examples check failed: none of the tools include examples. See how to fix → Fail
Stability & Change Management100
- No destabilizing schema changes in the last 30 days.Pass
Tool Coverage100
- 100% of tools have a non-trivial description (not blank, and not just the tool's name).Pass
- 100% of tool parameters carry a description.Pass
- Structured output schemas are declared (100% of tools); any adoption earns full credit.Pass
Tool Safety100
- No prompt-injection markers were found in the server instructions, tool names or descriptions we captured.Pass
- We read all 2 captured tool definition(s), and no name or description among them implies an irreversible operation.Pass
- An AI judge read all 2 captured unit(s) of tool text and found none that tries to manipulate the model reading it.Pass
Capabilities100
- Implements a supported MCP spec version (2025-11-25); the latest is 2026-07-28.Pass
How do I install the Subdomain API MCP server?
Subdomain API is a hosted endpoint at https://api.subdomain.app/mcp, so there is nothing to install locally. Ready-made configuration for Claude, Cursor, VS Code, Codex and 5 more is on this page, copied from each client's own documentation.
remote · api.subdomain.app
claude mcp add --transport http app-subdomain-subdomains 'https://api.subdomain.app/mcp'
{
"mcpServers": {
"app-subdomain-subdomains": {
"url": "https://api.subdomain.app/mcp"
}
}
} {
"servers": {
"app-subdomain-subdomains": {
"type": "http",
"url": "https://api.subdomain.app/mcp"
}
}
} [mcp_servers.app-subdomain-subdomains] url = "https://api.subdomain.app/mcp"
{
"$schema": "https://opencode.ai/config.json",
"mcp": {
"app-subdomain-subdomains": {
"type": "remote",
"url": "https://api.subdomain.app/mcp",
"enabled": true
}
}
} openclaw mcp add app-subdomain-subdomains --url 'https://api.subdomain.app/mcp' --transport streamable-http
mcp_servers:
app-subdomain-subdomains:
url: "https://api.subdomain.app/mcp" {
"McpServers": {
"app-subdomain-subdomains": {
"Transport": "http",
"Url": "https://api.subdomain.app/mcp"
}
}
} assistant mcp add app-subdomain-subdomains -t streamable-http -u 'https://api.subdomain.app/mcp'
{
"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.
Every change we have recorded for this component, newest first. Security-relevant changes are always shown. ▲ marks a change for the better, ▼ a change for the worse; unmarked changes are neutral.
- 26 Aug 26 +1
- We updated how we score, so this day's move reflects our rubric, not a change to the server See what changed → functional
- 25 Aug 26 0
- Stability: 0.97 → pass security
- 11 Aug 26 0
- We updated how we score, so this day's move reflects our rubric, not a change to the server See what changed → functional
- 31 Jul 26 0
- We updated how we score, so this day's move reflects our rubric, not a change to the server See what changed → functional
- 30 Jul 26 0
- We updated how we score, so this day's move reflects our rubric, not a change to the server See what changed → functional
- 27 Jul 26 0
- We updated how we score, so this day's move reflects our rubric, not a change to the server See what changed → functional
- 26 Jul 26 0
First indexed and scored.
Diagnostic detail from the automated scan of this channel: what the scanner observed at each step, so you can see exactly where a check passed or failed. It is informational only and never changes the trust score.
Captured 22 Sept 2026 · Probed https://api.subdomain.app/mcp
TLS valid
Negotiated TLS 1.3 with TLS_AES_128_GCM_SHA256 .
| Subject | Issuer | Valid from | Valid until | Key | Signature | Serial |
|---|---|---|---|---|---|---|
| CN=subdomain.app | CN=WE1,O=Google Trust Services,C=US | 15 Aug 2026 | 13 Nov 2026 | ECDSA 256 | ECDSA-SHA256 | f3851bfb7d6627ef0e9d7c947339be36 |
| SANs: subdomain.app, api.subdomain.app, *.api.subdomain.app | ||||||
| CN=WE1,O=Google Trust Services,C=US (CA) | CN=GTS Root R4,O=Google Trust Services LLC,C=US | 13 Dec 2023 | 20 Feb 2029 | ECDSA 256 | ECDSA-SHA384 | 7ff31977972c224a76155d13b6d685e3 |
| CN=GTS Root R4,O=Google Trust Services LLC,C=US (CA) | CN=GlobalSign Root CA,OU=Root CA,O=GlobalSign nv-sa,C=BE | 15 Nov 2023 | 28 Jan 2028 | ECDSA 384 | SHA256-RSA | 7fe530bf331343bedd821610493d8a1b |
Background: What to check on a remote MCP endpoint →
DNSSEC secure
Validation of api.subdomain.app. — Secure
| Zone | DS | Keys | Algorithms | Outcome |
|---|---|---|---|---|
| . | trust_anchor | 20326, 38696 | 8, 8 | Verified |
| app. | present | 23684 | 8 | Verified |
| subdomain.app. | present | 2371 | 13 | Verified |
| api.subdomain.app. | Verified address RRset verified with the apex keys |
Authentication No authorisation required
The endpoint answered without asking for a token. Anyone who knows the URL can reach it.
| Result | No authorisation required |
|---|---|
| HTTP status | 200 |
Background: How OAuth 2.1 works in the 2026 MCP spec →
Transports 2 probes
| Transport | URL | Outcome | Status | Location |
|---|---|---|---|---|
| streamable-http | https://api.subdomain.app/mcp | Verified | 200 | |
| http (plaintext) | http://api.subdomain.app/mcp | HTTPS enforced | 301 | https://api.subdomain.app/mcp |
The tools this component advertises to a client, with an estimated token cost for each. Expand a tool to see its parameters and schema. The per-tool counts are indicative and are not scored directly; the schema's total context footprint is one signal in Schema Quality & AI Usability. A tool's description is untrusted text the model reads on every call, which is what makes this list a security surface and not just an inventory: how tool poisoning works →
count_subdomains Count subdomains ~132
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.
| Name | Type | Req | Description |
|---|---|---|---|
| domain | string | yes | Root (registrable) domain as a bare hostname, e.g. "example.com". No scheme, path, port, or leading "www." — these are stripped. |
| Name | Type | Req | Description |
|---|---|---|---|
| domain | string | yes | – |
| total | integer | yes | Total distinct subdomains known. |
No examples provided.
find_subdomains Find subdomains ~212
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`.
| Name | Type | Req | Description |
|---|---|---|---|
| domain | string | yes | 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. |
| Name | Type | Req | Description |
|---|---|---|---|
| domain | string | yes | – |
| returned | integer | yes | Number in `subdomains`. |
| subdomains | array | yes | – |
| total | integer | yes | Total distinct subdomains known. |
| truncated | boolean | yes | True if more exist beyond `limit`. |
No examples provided.
What is the Subdomain API MCP server?
Subdomain API is an MCP server listed in the public MCP registry as app.subdomain/subdomains. Find known subdomains of a domain. Passive data; may include historic entries. List or count. This page covers its hosted endpoint (https://api.subdomain.app/mcp).
Is the Subdomain API MCP server safe to use?
Subdomain API scores 81 out of 100 on VerifyMCP. That is a record of what we were able to check automatically, not an endorsement. The category breakdown on this page shows every signal behind the number, including the ones we could not confirm.
What tools does the Subdomain API MCP server expose?
Subdomain API exposes 2 tools: find_subdomains, count_subdomains. Their descriptions and schemas cost roughly 344 tokens of context every time the server is loaded.
Does the Subdomain API MCP server require authentication?
No. We connected to Subdomain API without credentials and it answered, so anything it exposes is reachable by anyone who knows the address.
Is the Subdomain API MCP server still maintained?
Subdomain API is still listed as active in the MCP registry. We last reached this channel on 22 September 2026. Those dates come from our own scans of the registry and the channel itself, not from anything the publisher announced.