# Subdomain Discovery Lookup - Certificate Transparency API (`accountable_eel/subdomain-discovery-lookup`) Actor

Enumerate any domain's real subdomains from the free, public Certificate Transparency log API (certspotter) — no login, no scraping. Every subdomain returned had an actual TLS certificate issued for it. Pay only when subdomains are found; domains with no CT history cost nothing.

- **URL**: https://apify.com/accountable\_eel/subdomain-discovery-lookup.md
- **Developed by:** [Adrian Voss](https://apify.com/accountable_eel) (community)
- **Categories:** Lead generation, Developer tools
- **Stats:** 2 total users, 1 monthly users, 100.0% runs succeeded, 0 bookmarks
- **User rating**: No ratings yet

## Pricing

from $3.00 / 1,000 successful lookups

This Actor is paid per event. You are not charged for the Apify platform usage, but only a fixed price for specific events.
Since this Actor supports Apify Store discounts, the price gets lower the higher subscription plan you have.

Learn more: https://docs.apify.com/actors/running/actors-in-store.md#pay-per-event

## What's an Apify Actor?

Actors are web data automations that power AI and operations. They run on the Apify platform to scrape websites, process data, connect APIs, and automate workflows.
In Batch mode, an Actor accepts a well-defined JSON input, performs an action which can take anything from a few seconds to a few hours,
and optionally produces a well-defined JSON output, datasets with results, or files in key-value store.
In Standby mode, an Actor provides a web server which can be used as a website, API, or an MCP server.
Actors are written with capital "A".

## How to integrate an Actor?

If asked about integration, you help developers integrate Actors into their projects.
You adapt to their stack and deliver integrations that are safe, well-documented, and production-ready.
The best way to integrate Actors is as follows.

- **AI agents and MCP clients** — the [Apify MCP server](https://docs.apify.com/integrations/mcp.md) at `https://mcp.apify.com` (remote, streamable HTTP, OAuth on first use).
- **Agentic workflows and local Actor development** — [Agent Skills](https://apify.com/.well-known/agent-skills/index.json) with the [Apify CLI](https://docs.apify.com/cli/docs.md): `npm install -g apify-cli`, then `apify login`.
- **JavaScript/TypeScript projects** — the official [JS/TS client](https://docs.apify.com/api/client/js/docs.md): `npm install apify-client`.
- **Python projects** — the official [Python client](https://docs.apify.com/api/client/python/docs.md): `pip install apify-client`.
- **Any other language** — the [REST API](https://docs.apify.com/api/v2.md).

For usage examples, see the [API](#api) section below.

For more details, see Apify documentation as [Markdown index](https://docs.apify.com/llms.txt) and [Markdown full-text](https://docs.apify.com/llms-full.txt).

# README

## Subdomain Discovery Lookup

Look up any domain's real subdomains against the free, public
[Certificate Transparency](https://certificate.transparency.dev) log search API run by
SSLMate's [certspotter](https://sslmate.com/certspotter/) — every subdomain returned had an
actual TLS certificate issued for it at some point. No API key, no scraping — this hits the
official public CT-log API directly.

### Features

- **Domain → subdomain list.** Every hostname found in CT logs' certificate records for the
  domain and its subdomains, deduplicated and alphabetically sorted.
- **Certificate provenance.** Each subdomain comes with `firstSeenCertDate` — the earliest
  certificate issuance date on record for that hostname.
- **Wildcard-aware.** Wildcard certificate entries (`*.example.com`) are filtered out — only
  real, individually discovered hostnames are counted.
- **Pay only for hits.** Domains with no Certificate Transparency history cost nothing —
  see [Pricing](#pricing).
- **Built for bulk.** Feed in a list of domains; concurrency and Apify Proxy are configurable.

### How to use Subdomain Discovery Lookup - Certificate Transparency API

1. **In the Apify Console.** Open the actor page and click **Start** — the `items` field is already pre-filled with a working example. Results land in the run's dataset as soon as each item is found.
2. **Via the API.** Call it directly with a POST request — no Console needed once you have an API token:
   ```bash
   curl "https://api.apify.com/v2/acts/accountable_eel~subdomain-discovery-lookup/run-sync-get-dataset-items?token=<YOUR_TOKEN>" \
     -X POST \
     -H "Content-Type: application/json" \
     -d '{"items":["stripe.com"]}'
   ```
3. **On a schedule.** Save this actor as an Apify **Task** with the input you want, then add a **Schedule** (hourly, daily, weekly) so it runs on its own — no server of your own required.

### Input

```json
{
  "items": ["stripe.com", "example.com"],
  "maxConcurrency": 5,
  "proxyConfiguration": { "useApifyProxy": true }
}
```

`items` is a list of domains (or full URLs — protocol, path, and a leading `www.` are stripped
automatically) to enumerate subdomains for. `maxConcurrency` controls how many lookups run in
parallel (default 5, max 20) — kept conservative by default since this target has no browser
fallback if it starts blocking. `proxyConfiguration` configures Apify Proxy; defaults to Apify
Proxy enabled.

### Output

One row per input domain, for example:

```json
{
  "query": "stripe.com",
  "found": true,
  "data": {
    "domain": "stripe.com",
    "certificatesScanned": 842,
    "subdomainCount": 37,
    "subdomains": [
      { "hostname": "api.stripe.com", "firstSeenCertDate": "2014-03-11T00:00:00Z" },
      { "hostname": "dashboard.stripe.com", "firstSeenCertDate": "2015-07-02T00:00:00Z" }
    ],
    "truncated": false
  },
  "scrapedAt": "2026-08-20T12:00:00.000Z"
}
```

`subdomains` is capped at the first 1000 entries (alphabetical); `truncated: true` flags when a
domain has more than that. Domains with no matching certificates in CT logs come back as
`{ "query": "...", "found": false, "scrapedAt": "..." }` and are never charged.

### Use cases

- **Attack-surface mapping.** Enumerate every publicly certificate-issued hostname for a domain
  before a pentest or bug bounty engagement.
- **Security monitoring.** Track new subdomains appearing in Certificate Transparency logs to
  catch shadow IT, forgotten staging hosts, or unauthorized deployments.
- **M\&A and vendor due diligence.** Map a target company's real internet footprint from public
  certificate history, not just its marketing site.
- **Bulk domain audits.** Feed in a portfolio of company domains and get subdomain counts and
  hostnames back in a single run.

### Pricing

$5 per 1,000 results, plus a $0.005 start fee. Misses (`found:false`) are never charged.

### Use it from Clay, n8n, Make, or an AI agent

This actor runs synchronously over plain HTTP — call it directly from a script, a workflow tool, or an AI agent, no Apify Console needed once you have an API token.

```bash
curl "https://api.apify.com/v2/acts/accountable_eel~subdomain-discovery-lookup/run-sync-get-dataset-items?token=<YOUR_TOKEN>" \
  -X POST \
  -H "Content-Type: application/json" \
  -d '{"items":["stripe.com"]}'
```

**n8n.** Add an HTTP Request node: Method `POST`, URL `https://api.apify.com/v2/acts/accountable_eel~subdomain-discovery-lookup/run-sync-get-dataset-items?token=<YOUR_TOKEN>`, Body Content Type `JSON`, JSON Body `{"items":["stripe.com"]}` (swap in an expression from an earlier node for a real value).

**Clay.** Add an "HTTP API" column: Method `POST`, URL `https://api.apify.com/v2/acts/accountable_eel~subdomain-discovery-lookup/run-sync-get-dataset-items?token=<YOUR_TOKEN>`, Body `{"items":["{{value}}"]}`, mapping the row's value into the `items` array.

**MCP.** In Claude, Cursor, or any MCP client with the Apify MCP server, ask for "Subdomain Discovery Lookup - Certificate Transparency API..." — the agent will find and run this actor.

### FAQ

**What counts as a "found" result?**
Any input domain where certspotter's issuances API returns at least one certificate whose
`dns_names` include the domain itself or a genuine subdomain of it. If the API returns no
certificates, or nothing survives wildcard filtering, the row comes back `found: false` and
isn't charged.

**Do I need to strip `https://` or `www.` from my input?**
No — domain normalization strips the protocol, any path, and a leading `www.` automatically
before querying.

**Is there a limit on how many subdomains are returned per domain?**
Yes, results are capped at 1000 subdomains per domain, alphabetically sorted; `data.truncated`
is `true` when a domain has more than that.

**Does this need my own API key or login?**
No — it hits certspotter's free public `issuances` endpoint with no authentication.

**How does concurrency and proxy work?**
`maxConcurrency` (default 5, max 20) controls parallel requests; it's kept conservative by
default because this actor has no browser fallback if the target starts blocking. `proxyConfiguration`
defaults to Apify Proxy; consider residential proxies if you hit rate limits at high concurrency.

**Can I pass thousands of domains in one run?**
Yes — `items` accepts any list length; each domain is billed independently and processed at the
configured concurrency.

# Actor input Schema

## `items` (type: `array`):

One item per line — see the item shape and examples below. Only the items we actually find are charged — never per run, and never for a miss.

## `maxConcurrency` (type: `integer`):

Parallel requests. Keep conservative — this target has no browser fallback, so getting blocked costs more than slow-and-steady.

## `proxyConfiguration` (type: `object`):

Apify Proxy config. Residential recommended for anti-bot-sensitive targets.

## Actor input object example

```json
{
  "items": [
    "stripe.com"
  ],
  "maxConcurrency": 5,
  "proxyConfiguration": {
    "useApifyProxy": true
  }
}
```

# Actor output Schema

## `results` (type: `string`):

No description

# API

You can run this Actor programmatically using our API. Below are code examples in JavaScript, Python, and CLI, as well as the OpenAPI specification and MCP server setup.

## JavaScript example

```javascript
import { ApifyClient } from 'apify-client';

// Initialize the ApifyClient with your Apify API token
// Replace the '<YOUR_API_TOKEN>' with your token
const client = new ApifyClient({
    token: '<YOUR_API_TOKEN>',
});

// Prepare Actor input
const input = {
    "items": [
        "stripe.com"
    ]
};

// Run the Actor and wait for it to finish
const run = await client.actor("accountable_eel/subdomain-discovery-lookup").call(input);

// Fetch and print Actor results from the run's dataset (if any)
console.log('Results from dataset');
console.log(`💾 Check your data here: https://console.apify.com/storage/datasets/${run.defaultDatasetId}`);
const { items } = await client.dataset(run.defaultDatasetId).listItems();
items.forEach((item) => {
    console.dir(item);
});

// 📚 Want to learn more 📖? Go to → https://docs.apify.com/api/client/js/docs

```

## Python example

```python
from apify_client import ApifyClient

# Initialize the ApifyClient with your Apify API token
# Replace '<YOUR_API_TOKEN>' with your token.
client = ApifyClient("<YOUR_API_TOKEN>")

# Prepare the Actor input
run_input = { "items": ["stripe.com"] }

# Run the Actor and wait for it to finish
run = client.actor("accountable_eel/subdomain-discovery-lookup").call(run_input=run_input)

# Fetch and print Actor results from the run's dataset (if there are any)
print(f"💾 Check your data here: https://console.apify.com/storage/datasets/{run.default_dataset_id}")
for item in client.dataset(run.default_dataset_id).iterate_items():
    print(item)

# 📚 Want to learn more 📖? Go to → https://docs.apify.com/api/client/python/docs/quick-start

```

## CLI example

```bash
echo '{
  "items": [
    "stripe.com"
  ]
}' |
apify call accountable_eel/subdomain-discovery-lookup --silent --output-dataset

```

## MCP server setup

```json
{
    "mcpServers": {
        "apify": {
            "type": "http",
            "url": "https://mcp.apify.com/?tools=fetch-actor-details,accountable_eel/subdomain-discovery-lookup"
        }
    }
}

```

The hosted server signs you in with OAuth on first connect, so no API token belongs in this config. Clients without OAuth support can send an `Authorization: Bearer <APIFY_API_TOKEN>` header instead, using a token from API & Integrations in Apify Console (https://console.apify.com/settings/integrations).

## OpenAPI specification

Download the OpenAPI definition: https://api.apify.com/v2/actors/HfKnev1zf8Eh9t85z/builds/bqqDfTYfLwL2whls1/openapi.json