# CT Subdomain Finder & New Certificate Alerts · SiteVerdict (`siteverdict/siteverdict-ct-subdomain-monitor`) Actor

Find every subdomain of your domains from Certificate Transparency logs (crt.sh or your Cert Spotter key): first/last seen, issuers, wildcards, live DNS and dangling-CNAME takeover hints. Monitor mode alerts you to new hosts and certificates via Slack or webhook.

- **URL**: https://apify.com/siteverdict/siteverdict-ct-subdomain-monitor.md
- **Developed by:** [Aman Thakran](https://apify.com/siteverdict) (community)
- **Categories:** Developer tools
- **Security:** Limited permissions
- **Stats:** 2 total users, 1 monthly users, 100.0% runs succeeded, 0 bookmarks
- **User rating**: No ratings yet

## Pricing

$15.00 / 1,000 domain scanneds

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

## CT Subdomain Finder & New Certificate Alerts — know every host on your domain

**Every TLS certificate is published in public Certificate Transparency (CT) logs. SiteVerdict turns those logs into a clean inventory of your subdomains and alerts you the day a new host or certificate appears** — forgotten staging servers, shadow-IT SaaS, a vendor issuing certificates for your brand, or an attacker's phishing host on a dangling DNS record.

- 🔎 **Full subdomain inventory** from CT: first/last seen, latest expiry, issuers, certificate count
- ✳️ **Wildcard aware**: `*.example.com` kept as its own row; hosts covered by a wildcard are marked
- 🟢 **Live check by DNS** (A/AAAA/CNAME) — no web requests to your hosts
- ⚠️ **Takeover hints**: CNAMEs to S3, Azure, Heroku, GitHub Pages, Shopify, Zendesk and 40 other services that no longer resolve
- 🔔 **Monitor mode**: new hosts flagged `isNew`, sent to Slack or your webhook
- 🐢 **Polite to free services**: one crt.sh query per domain, long timeouts, careful retries and a 12-hour cache; or use your own Cert Spotter API key

### Who it is for

1. **Security teams and pentesters (authorised scope)** — attack-surface discovery and continuous monitoring of your own domains.
2. **IT and DevOps** — find forgotten hosts and certificates before they expire or get hijacked.
3. **Agencies and MSPs** — a weekly "new hosts" digest for every client domain.

### Example output

```json
{
  "recordType": "subdomain",
  "domain": "sample-shop.example",
  "host": "help.sample-shop.example",
  "isNew": true,
  "wildcard": false,
  "coveredByWildcard": true,
  "resolves": false,
  "cname": "help-sample-shop.s3-website.eu-west-2.amazonaws.com",
  "takeoverHint": "CNAME points to help-sample-shop.s3-website.eu-west-2.amazonaws.com (s3-website) which does not resolve - possible dangling record / subdomain takeover risk. Verify and remove the record if unused.",
  "activeCert": true,
  "firstSeen": "2026-01-05T00:00:00.000Z",
  "latestExpiry": "2027-02-05T00:00:00.000Z",
  "issuers": ["Amazon"]
}
```

Each domain also gets a `domain-summary` row: certificates, subdomains, valid-cert count, resolving count, wildcards, new hosts and takeover hints.

**Before:** "Do we have anything else on our domain?" — **After:** a sorted list of 140 hosts, 3 of them new this week and 1 dangling CNAME to fix today.

### How to use

1. Enter your domains (e.g. `example.com`).
2. Keep **crt.sh** (free) or choose **Cert Spotter** and paste your API key for faster, more reliable results.
3. For monitoring: turn on **Monitor mode** (+ **Only output new subdomains**), add a Slack/webhook URL and schedule daily. The first run is the baseline.

### Pricing

| Event | Price (proposed) |
|---|---|
| Domain scanned (`domain-scanned`) — all subdomains, DNS checks and takeover hints for one domain | $0.015 |

Examples: **10 domains ≈ $0.15**; daily monitoring of 5 domains ≈ **$2.25 a month**. Failed CT queries (e.g. crt.sh down) and sample mode are free.

### Benchmark (honest summary)

Compared with subdomain / CT Actors on the Apify Store by documented features (we did not run them):

| | SiteVerdict | Typical CT/subdomain finders |
|---|---|---|
| CT source | crt.sh (cached, polite) or Cert Spotter with your key | crt.sh only, or brute-force DNS wordlists |
| New-host monitoring + Slack/webhook | ✅ | Rare |
| Wildcard handling | ✅ separate rows + "covered by wildcard" | Usually stripped or mixed |
| DNS liveness + dangling-CNAME takeover hints | ✅ | Rare |
| Brute force / active probing | ❌ never (passive only) | Often |
| Price | $0.015 per domain | $0.02 per domain or per-row pricing |

Caveat: crt.sh is a free community service and is sometimes too slow for very large domains (e.g. big tech). Those runs are reported as failed (not charged); use Cert Spotter with your own key.

### FAQ

**Is this legal?** CT logs are public by design (RFC 6962/9162) and we only read them. DNS lookups are ordinary public queries. We never probe, scan ports or brute-force. Only monitor domains you own or are authorised to assess.

**Why are some hosts not resolving?** CT shows every name that ever had a certificate. Old hosts disappear from DNS; that is useful history (and the source of takeover risk).

**Will internal hostnames leak?** Only names already published in public CT logs appear — which is exactly why you should know about them.

### Limits

- Max 200 domains per run; up to 20,000 subdomains per domain; up to 5,000 DNS checks per domain (default 500).
- crt.sh: one query per domain, 10 s between domains by default, up to 3 attempts with 20–40 s backoff; responses up to 60 MB.
- Cert Spotter: up to 50 pages per domain; without a key the free quota is small.
- Passive only: no HTTP requests to discovered hosts.

### Sources & compliance

- crt.sh, operated by Sectigo — public CT search, https://crt.sh/ (read 11 Oct 2026). No published terms forbid automated JSON queries; we follow its etiquette: one query per domain, caching, honest User-Agent `SiteVerdict/ct-subdomain-monitor` with contact aman.thakran@bharatfare.com.
- Cert Spotter API by SSLMate — https://sslmate.com/help/reference/ct_search_api_v1 and terms https://sslmate.com/terms (read 11 Oct 2026); used with the user's own key.
- Takeover service list: service names compiled from the public "can-i-take-over-xyz" project (MIT) — names only, no code.
- No personal data is collected. Certificates sometimes contain email-like SANs; these are dropped. UK GDPR/PECR: none of the output is personal data unless your hostnames contain personal names.
- Secrets (Cert Spotter key, webhook URLs) are encrypted inputs, never logged or output.
- Not legal advice; takeover hints are signals to verify, not proof.

# Changelog

This Actor's version history is a separate document: https://apify.com/siteverdict/siteverdict-ct-subdomain-monitor/changelog.md

# Actor input Schema

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

Registered domains or subdomains to search, e.g. example.com (max 200 per run). Public suffixes such as co.uk are refused.

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

crt.sh is free but often slow or briefly unavailable; we query it once per domain, politely, and cache results. Cert Spotter (SSLMate) is faster and more reliable with your own API key.

## `certSpotterApiKey` (type: `string`):

Optional, your own key from sslmate.com/certspotter. Without it Cert Spotter allows only a small number of requests. Stored encrypted, never logged.

## `excludeExpired` (type: `boolean`):

Off = full history (finds old, forgotten hosts). On = only currently valid certificates (crt.sh).

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

Resolves A/AAAA/CNAME so you can see which hosts are live, and flags dangling CNAMEs to services such as S3, Azure, Heroku or GitHub Pages (possible subdomain takeover). DNS only - no web requests to your hosts.

## `onlyActive` (type: `boolean`):

Only subdomains with a valid certificate.

## `sampleMode` (type: `boolean`):

Switched on automatically when no domains are given.

## `monitorMode` (type: `boolean`):

Remembers the subdomains seen per domain in a named key-value store; later runs mark new hosts (isNew) and list them in the domain summary. Schedule daily.

## `monitorStateName` (type: `string`):

Stored as siteverdict-ct-<name>.

## `onlyNew` (type: `boolean`):

In monitor mode, push only new hosts (and takeover hints) plus the per-domain summary.

## `slackWebhookUrl` (type: `string`):

Optional. One message per run listing new hosts and takeover hints. Stored encrypted, never logged.

## `webhookUrl` (type: `string`):

Optional HTTPS endpoint. Stored encrypted, never logged.

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

Max subdomains per domain.

## `maxDnsChecksPerDomain` (type: `integer`):

Most recently seen hosts are checked first.

## `cacheHours` (type: `integer`):

CT answers are cached in your account (siteverdict-ct-cache) to avoid repeating heavy queries against free services. 0 = always query.

## `delayBetweenDomainsSecs` (type: `integer`):

Minimum 5 s for crt.sh (1 s for Cert Spotter).

## Actor input object example

```json
{
  "domains": [
    "example.com"
  ],
  "source": "crtsh",
  "excludeExpired": false,
  "resolveDns": true,
  "onlyActive": false,
  "sampleMode": false,
  "monitorMode": false,
  "monitorStateName": "default",
  "onlyNew": false,
  "maxSubdomainsPerDomain": 5000,
  "maxDnsChecksPerDomain": 500,
  "cacheHours": 12,
  "delayBetweenDomainsSecs": 10
}
```

# Actor output Schema

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

No description

## `output` (type: `string`):

No description

## `files` (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": [
        "example.com"
    ]
};

// Run the Actor and wait for it to finish
const run = await client.actor("siteverdict/siteverdict-ct-subdomain-monitor").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": ["example.com"] }

# Run the Actor and wait for it to finish
run = client.actor("siteverdict/siteverdict-ct-subdomain-monitor").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": [
    "example.com"
  ]
}' |
apify call siteverdict/siteverdict-ct-subdomain-monitor --silent --output-dataset

```

## MCP server setup

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

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/X5ZsVzeYAzTf5WLjE/builds/Iqe24eAGBxewuPaOW/openapi.json