# Crt Sh Subdomain Finder (`zerobreak/crt-sh-subdomain-finder`) Actor

crt.sh Subdomain Finder is a Python tool to extract subdomains, certificate details, and issuance dates from the crt.sh public SSL database. It exports structured security datasets into clean CSV or JSON formats for network reconnaissance and asset discovery.

- **URL**: https://apify.com/zerobreak/crt-sh-subdomain-finder.md
- **Developed by:** [ZeroBreak](https://apify.com/zerobreak) (community)
- **Security:** Limited permissions
- **Stats:** 2 total users, 1 monthly users, 100.0% runs succeeded, 0 bookmarks
- **User rating**: No ratings yet

## Pricing

from $2.99 / 1,000 results

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?

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

### crt.sh Subdomain Finder — Certificate Transparency Subdomain Discovery

![crt.sh Subdomain Finder cover](https://images.bigibyte.com/cdn-cgi/image/width=1260,height=540,fit=cover,format=webp/apify-actors-covers/crt-sh-subdomain-finder-cover.png)

### Overview

Discover subdomains associated with a domain using publicly available Certificate Transparency (CT) records from crt.sh.

Provide one or more domains, and this actor extracts hostnames found in certificate records, organizes them into individual subdomain entries, and removes duplicate certificate and hostname combinations.

You can optionally exclude expired certificates and control the maximum number of results collected per run.

### Features

- Discover subdomains from public Certificate Transparency records.
- Accept multiple domains as input.
- Extract hostnames from certificate records.
- Collect certificate and issuer information.
- Optionally exclude expired certificates.
- Remove duplicate certificate and hostname combinations.
- Set a maximum number of results per run.
- Export results in JSON, CSV, Excel, and other supported formats.

### Collection Mode

**Subdomains**

Collects certificate records for supplied domains and extracts the associated hostnames as structured subdomain entries.

### Use Cases

- **Attack Surface Mapping:** Discover hostnames associated with a domain for authorized security assessments.
- **Asset Inventory:** Build structured lists of known subdomains for domain management.
- **Brand Monitoring:** Identify unexpected or unfamiliar hostnames appearing in certificate records.
- **Security Research:** Review publicly recorded certificate and issuer information.
- **Domain Research:** Organize discovered subdomains for further investigation.
- **Lead Enrichment:** Identify publicly visible product, regional, or service-related hostnames associated with a company domain.

### Input Parameters

| Parameter | Type | Description |
|---|---|---|
| `mode` | String | Collection mode. Use `subdomains` to discover subdomains. |
| `domains` | Array | List of domains to search. |
| `excludeExpired` | Boolean | Set to `true` to skip certificates that have expired. |
| `maxItems` | Integer | Maximum number of results to collect. |
| `requestDelaySecs` | Number | Delay between requests. |

### Example Input

```json id="crtsh01"
{
  "mode": "subdomains",
  "domains": [
    "apify.com"
  ],
  "excludeExpired": false,
  "maxItems": 50,
  "requestDelaySecs": 1
}
```

### What Data Does This Actor Extract?

| Field | Description |
|---|---|
| `subdomain` | Discovered hostname associated with the supplied domain. |
| `domain` | Original domain used for the lookup. |
| `commonName` | Certificate common name. |
| `certId` | Certificate record identifier. |
| `issuerName` | Certificate issuer name. |
| `issuerCaId` | Certificate authority identifier. |
| `notBefore` | Certificate validity start date. |
| `notAfter` | Certificate expiration date. |
| `serialNumber` | Certificate serial number. |
| `scraped_at` | Date and time the result was collected. |

### Example Output

```json id="crtsh02"
{
  "subdomain": "affiliate.apify.com",
  "domain": "apify.com",
  "commonName": "affiliate.apify.com",
  "certId": 29951075522,
  "issuerName": "C=US, O=Let's Encrypt, CN=YR2",
  "issuerCaId": 432477,
  "notBefore": "2026-10-09T21:27:57",
  "notAfter": "2027-01-07T21:27:56",
  "serialNumber": "05c10dfb5a4b5ba72b1a699d9ab483e4752f",
  "scraped_at": "2026-10-26T00:00:00+00:00"
}
```

### Working with Your Dataset

After the run finishes, open the **Dataset** tab to review your discovered subdomains and certificate details.

You can export the results in formats such as:

- JSON
- CSV
- Excel
- XML
- HTML

Use the exported data to maintain domain inventories, review certificate history, or support authorized security research.

### FAQ

**Who is this actor for?**

It is useful for security researchers, domain administrators, developers, and analysts who need structured subdomain discovery results.

**What is Certificate Transparency?**

Certificate Transparency is a public system that records issued digital certificates. These records can reveal hostnames included in certificates.

**Can I search multiple domains?**

Yes. Add multiple domain names to the `domains` input array.

**Does it collect only active subdomains?**

No. Certificate records can contain hostnames that are no longer active. Certificate Transparency records do not confirm that a hostname currently resolves or hosts a working website.

**What does `excludeExpired` do?**

When enabled, the actor skips certificates whose expiration date has passed. Hostnames found only in expired certificates will not be included.

**Can I schedule recurring runs?**

Yes. Use Apify Schedules to run the actor automatically at your preferred interval.

**What export formats are supported?**

You can export the dataset in JSON, CSV, Excel, and other supported formats.

**Why might some lookups return incomplete results?**

Certificate Transparency services may occasionally be slow or temporarily unavailable. Results also depend on the certificate records available for each domain.

### Disclaimer

This Actor is an independent tool and is not affiliated with, endorsed by, sponsored by, or officially associated with crt.sh, Sectigo, or their owners. It collects publicly available certificate information. Users are responsible for ensuring that their use of the collected data complies with applicable laws and relevant terms of use. Only investigate domains and systems you own or are authorized to assess.

### Is Web Scraping Legal?

Collecting information that is already public is generally legal. There is no single law that bans all forms of web scraping. The limits are the usual ones: do not break into accounts, do not take private or confidential data, and be careful with personal data and copyrighted works. A site's terms can also restrict how you access it. Facts such as a public name, price, or rating are not the same thing as republishing someone's article or photo.

This actor collects information from public pages. It does not log in and it does not bypass access controls.

For a longer explanation, see Apify's article [Is web scraping legal?](https://blog.apify.com/is-web-scraping-legal/).

# Actor input Schema

## `mode` (type: `string`):

What to scrape. Subdomains queries crt.sh certificate transparency JSON for each domain.

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

Domains to look up on crt.sh, one per line.

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

Skip certificates whose not_after is in the past.

## `maxItems` (type: `integer`):

Stop after this many successful rows. Hard max is 1000.

## `requestDelaySecs` (type: `number`):

Seconds to wait between requests.

## `userAgent` (type: `string`):

User-Agent header sent with each request.

## `timeoutSecs` (type: `integer`):

Overall run budget in seconds.

## `requestTimeoutSecs` (type: `integer`):

Per-request timeout in seconds. crt.sh can be slow; raise this if you see timeouts.

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

Optional proxy. Leave off unless you need it.

## Actor input object example

```json
{
  "mode": "subdomains",
  "domains": [
    "apify.com"
  ],
  "excludeExpired": false,
  "maxItems": 100,
  "requestDelaySecs": 1,
  "userAgent": "ActorResearch/1.0",
  "timeoutSecs": 300,
  "requestTimeoutSecs": 30,
  "proxyConfiguration": {
    "useApifyProxy": false
  }
}
```

# Actor output Schema

## `overview` (type: `string`):

Dataset rows in the overview table.

## `dataset` (type: `string`):

Full dataset for this run.

## `items` (type: `string`):

Dataset items as JSON.

# 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("zerobreak/crt-sh-subdomain-finder").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("zerobreak/crt-sh-subdomain-finder").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 zerobreak/crt-sh-subdomain-finder --silent --output-dataset

```

## MCP server setup

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

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/Uycgp3vMenV0uEIGO/builds/JVTtIPDbg1vdlxSX9/openapi.json