# Subdomain Finder - Certificate Transparency + DNS Check (`zhucl1006/subdomain-finder-certificate-transparency`) Actor

Find all subdomains of any domain from public Certificate Transparency logs (crt.sh, Cert Spotter fallback) with first-seen date, cert count, issuers and live DNS/IP check. Passive OSINT, no port scanning. For security teams and bug bounty. $2 per 1,000 subdomains.

- **URL**: https://apify.com/zhucl1006/subdomain-finder-certificate-transparency.md
- **Developed by:** [leo zhu](https://apify.com/zhucl1006) (community)
- **Stats:** 2 total users, 1 monthly users, 100.0% runs succeeded, 0 bookmarks
- **User rating**: No ratings yet

## Pricing

from $2.00 / 1,000 subdomains

This Actor is paid per event. You are not charged for the Apify platform usage, but only a fixed price for specific events.

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

## What's an Apify Actor?

An Actor is a serverless cloud program that runs on the Apify platform. It has two run modes.
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.

Apify vocabulary and the platform model are defined once, in the agent quickstart at https://apify.com/agents.md.

## 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.

Do not guess an integration path. Every one of them is in the agent quickstart at https://apify.com/agents.md: the Apify MCP server, Agent Skills with the Apify CLI, the JavaScript and Python clients, the REST API, and the account-free path for an agent with no human to sign in. It also carries the rule on stating cost before the first paid run.

For examples already wired to this Actor's own input schema, see the [API](#api) section below.

Each client library has reference documentation the quickstart does not restate: [JavaScript/TypeScript](https://docs.apify.com/api/client/js/docs.md) (`npm install apify-client`) and [Python](https://docs.apify.com/api/client/python/docs.md) (`pip install apify-client`).

# README

## Subdomain Finder - Certificate Transparency (crt.sh) + DNS Check

Find **all known subdomains** of any domain from public **Certificate Transparency (CT) logs** - every TLS certificate issued since ~2013 is logged publicly - and check which ones are **still live in DNS**. Uses **crt.sh** (full history) with automatic fallback to **Cert Spotter** when crt.sh is slow or down. 100% passive: no brute force, no port scanning, no login.

### Who uses it

- **Security teams & pentesters**: map the external attack surface, spot forgotten staging / admin / dev hosts.
- **Bug bounty hunters**: fast recon for many targets in one run, scheduled to catch new subdomains.
- **IT & compliance**: inventory company assets and certificates, find certs about to expire and which CAs are used.
- **Sales & market research**: see which SaaS a company runs (status., shop., help., jira., vpn. ...) and when new products went live (first certificate date).
- **Domain investors & SEO**: discover all sites under a brand.

### Input

| Field | Description |
|---|---|
| `domains` | Root domains (URLs are cleaned). |
| `source` | `auto` (default), `crtsh`, `certspotter` or `both`. |
| `resolveDns` | Resolve each subdomain and return IPs. |
| `onlyResolving` | Return only live subdomains (dead ones are not charged). |
| `includeExpired` | Use expired certificates too (finds old hosts). |
| `includeWildcards` | Keep `*.example.com` rows. |
| `maxSubdomainsPerDomain` | Default 1000. |

```json
{ "domains": ["example.com", "example.org"], "source": "both", "onlyResolving": true }
```

### Output (one row per subdomain)

```json
{
  "domain": "apify.com",
  "subdomain": "blog.apify.com",
  "resolves": true,
  "ipAddresses": ["104.18.12.34"],
  "firstCertSeen": "2017-10-10",
  "latestCertExpires": "2026-10-06",
  "certificateCount": 120,
  "issuers": ["Cloudflare", "Let's Encrypt", "Sectigo Limited"],
  "hasWildcardCert": false,
  "level": 1,
  "source": "crtsh",
  "url": "https://blog.apify.com"
}
```

A `RUN_SUMMARY` record (counts per source, failures) is saved in the key-value store.

### Pricing (pay per event)

- **$0.002 per subdomain saved** (`subdomain`) - $2 per 1,000.
- Tiny start fee per run (`apify-actor-start`).
- Invalid / failed domains and subdomains skipped by `onlyResolving` are not charged. Set "Maximum cost per run" to cap spend.

### Notes

- Only hostnames that ever appeared in a public TLS certificate are found (internal hosts without public certs and hosts covered only by a wildcard certificate are not visible in CT logs).
- crt.sh is a free community service and can be slow for very large domains (e.g. google.com); the Actor retries and falls back to Cert Spotter (current certificates only, free anonymous quota). Not affiliated with Sectigo (crt.sh) or SSLMate (Cert Spotter).
- Use responsibly and only for assets you are allowed to assess.

### FAQ

**Does it scan or brute-force?** No - it only reads public CT logs and does normal DNS lookups.
**Can I monitor for new subdomains?** Yes - schedule it and compare `firstCertSeen` with your last run.

# Actor input Schema

## `domains` (type: `array`):

Root domains (example.com). URLs are accepted and cleaned.

## `source` (type: `string`):

Source.

## `resolveDns` (type: `boolean`):

Resolve each subdomain and return its IP addresses.

## `onlyResolving` (type: `boolean`):

Skip subdomains that no longer resolve (they are not charged).

## `includeExpired` (type: `boolean`):

crt.sh: also use expired certificates (finds old / forgotten hosts).

## `includeWildcards` (type: `boolean`):

Keep \*.example.com rows instead of folding them into the base name.

## `maxSubdomainsPerDomain` (type: `integer`):

Max subdomains per domain.

## Actor input object example

```json
{
  "domains": [
    "apify.com"
  ],
  "source": "auto",
  "resolveDns": true,
  "onlyResolving": false,
  "includeExpired": true,
  "includeWildcards": false,
  "maxSubdomainsPerDomain": 1000
}
```

# Actor output Schema

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

No description

## `runSummary` (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 = {
    "domains": [
        "apify.com"
    ]
};

// Run the Actor and wait for it to finish
const run = await client.actor("zhucl1006/subdomain-finder-certificate-transparency").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 = { "domains": ["apify.com"] }

# Run the Actor and wait for it to finish
run = client.actor("zhucl1006/subdomain-finder-certificate-transparency").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 '{
  "domains": [
    "apify.com"
  ]
}' |
apify call zhucl1006/subdomain-finder-certificate-transparency --silent --output-dataset

```

## MCP server setup

```json
{
    "mcpServers": {
        "apify": {
            "type": "http",
            "url": "https://mcp.apify.com/?tools=fetch-actor-details,zhucl1006/subdomain-finder-certificate-transparency"
        }
    }
}
```

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/hlRvbIoyT0wMHWSFb/builds/evcCHiN188uCZYSzK/openapi.json