# Subdomain Finder – Certificate Transparency (`datascraperes/crt-name-subdomain-finder`) Actor

Find unique subdomains for up to 10,000 domains from live Certificate Transparency records. Normalize URLs, remove wildcard and duplicate hostnames, export structured results, and automate passive asset discovery through the Apify API.

- **URL**: https://apify.com/datascraperes/crt-name-subdomain-finder.md
- **Developed by:** [DataScraperES](https://apify.com/datascraperes) (community)
- **Categories:** Developer tools, SEO tools, Automation
- **Stats:** 2 total users, 1 monthly users, 100.0% runs succeeded, 0 bookmarks
- **User rating**: No ratings yet

## Pricing

from $0.45 / 1,000 subdomain 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?

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

Find unique subdomains for one or many websites from public Certificate Transparency records. Enter a domain or URL and receive **clean, deduplicated hostnames ready for export or automation** in the Apify Dataset.

### What this Actor does

The Actor searches public certificate transparency data exposed by crt.name for each submitted website. It normalizes URLs and subdomains to the registrable apex domain, removes duplicate and wildcard entries, filters unrelated hostnames, and returns one structured Dataset item per discovered hostname.

### Use cases

- Map a company's public web footprint before security or asset-inventory work
- Find regional, product, documentation, API, staging, and support hostnames
- Enrich domain lists for SEO, competitive research, and lead qualification
- Monitor certificate-derived hostname coverage across multiple domains

### How to use

1. Open the Actor in Apify Console.
2. Enter one or more domains or URLs in **Domains or URLs**.
3. Choose whether to include the apex domain and set an optional result limit.
4. Click **Start** and open the Dataset when the run finishes.

### Input

`domains` accepts between 1 and 10,000 domains or URLs. Values are converted to lowercase registrable domains and deduplicated, so `https://www.similarweb.com/path` and `similarweb.com` produce one search. By default, the apex domain itself is excluded and up to 10,000 hostnames are saved per domain. Request concurrency is managed automatically by the Actor. Large runs can take longer when the public source responds slowly or retries temporary errors.

```json
{
  "domains": [
    "similarweb.com"
  ],
  "includeApex": false,
  "maxResultsPerDomain": 3
}
```

### Output

Results are stored in the default Dataset and can be exported as JSON, CSV, Excel, XML, or RSS. A `found` item represents one hostname. Domains with no matching hostnames produce one `not_found` item; failed source requests produce one `failed` item with a safe error message so batch runs retain their partial results. The default Key-Value Store also contains a `SUMMARY` record with submitted and normalized domain counts plus aggregate result and billing counts.

This is the complete Dataset item from a real successful run:

```json
{
  "apexDomain": "similarweb.com",
  "subdomain": "academy.similarweb.com",
  "relativeName": "academy",
  "depth": 1,
  "isApex": false,
  "status": "found",
  "totalFoundForDomain": 121,
  "truncated": true,
  "sourceUrl": "https://crt.name/v1/search?apex=similarweb.com",
  "retrievedAt": "2026-08-24T12:51:00.625171Z",
  "error": null
}
```

### Pricing

Each successfully delivered unique subdomain triggers one `subdomain-result` event. Your Apify subscription tier determines its price:

| Apify user tier | Price per found subdomain |
|---|---:|
| Free | $0.0006 |
| Bronze | $0.00054 |
| Silver | $0.00048 |
| Gold | $0.00045 |
| Platinum | $0.00045 |
| Diamond | $0.00045 |

A charge occurs only for a Dataset item with `status: "found"`. `not_found` and `failed` diagnostics, duplicates, retries, and `SUMMARY` are not charged.

You can set a maximum charge for each run in Apify. If the remaining budget cannot cover every discovered hostname, the Actor saves and charges only the results that fit, marks `chargeLimitReached: true` in `SUMMARY`, and stops without delivering unpaid rows.

### API and integrations

Run the Actor through the Apify API, schedule recurring searches, trigger runs from webhooks, or connect the Dataset to downstream tools. Dataset exports work with common spreadsheet, database, and automation workflows without additional transformation.

### Related Actors

| Actor | Best for |
|---|---|
| [Similarweb Website Traffic & SEO Analytics Scraper](https://apify.com/datascraperes/similarweb-website-scraper) | Add traffic, ranking, audience, and competitor context to the domains you investigate. |
| [Website Technology Lookup – CMS, Hosting & Tech Stack Data](https://apify.com/datascraperes/website-technology-lookup) | Identify the published technologies, CMS, and hosting behind discovered web properties. |
| [Bulk Domain Rating Checker](https://apify.com/datascraperes/bulk-domain-rating-checker) | Compare authority metrics for domains after completing asset discovery. |
| [Favicon Extractor](https://apify.com/datascraperes/favicon-extractor) | Enrich discovered hostnames with favicon URLs and image metadata. |

### Limits and data quality

Certificate transparency records show hostnames present in public certificates; they do not prove that a hostname is currently live, reachable, owned by the same organization, or complete. Recently issued certificates may take time to appear, and hostnames that have never appeared in a public certificate cannot be discovered this way. The Actor retries temporary source failures, reports permanent per-domain failures, and marks every returned item with `truncated: true` when the configured per-domain limit omits additional matches.

### Frequently asked questions

#### Does the Actor check whether each subdomain is online?

No. It discovers certificate-derived hostnames and does not perform DNS resolution, HTTP probing, port scanning, or takeover checks.

#### Can I submit full URLs or subdomains?

Yes. The Actor extracts the hostname and converts it to the registrable apex domain. Paths, query strings, capitalization, leading `www`, and duplicate inputs do not create duplicate searches.

#### Why is a known subdomain missing?

It may not have appeared in a public certificate, the source may not have indexed it yet, or your `maxResultsPerDomain` value may have truncated the output. Check `totalFoundForDomain` and `truncated` in the Dataset item.

### Responsible use

Use the Actor only for lawful purposes and handle discovered infrastructure data responsibly. You are responsible for complying with applicable laws, privacy requirements, source terms, and authorization requirements before performing any follow-up testing against discovered hosts.

### Support

Open an issue in the Actor's **Issues** tab and include the run ID, a reproducible input, and the unexpected result. Do not include passwords, API tokens, or other secrets.

# Actor input Schema

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

Enter up to 10,000 domains or URLs. URLs and subdomains are reduced to their registrable apex domain, converted to lowercase, and deduplicated.

## `includeApex` (type: `boolean`):

Include the registrable domain itself when the source returns it. Disable this to receive subdomains only.

## `maxResultsPerDomain` (type: `integer`):

Maximum number of unique hostnames saved for each normalized apex domain after the apex-domain filter is applied.

## Actor input object example

```json
{
  "domains": [
    "similarweb.com"
  ],
  "includeApex": false,
  "maxResultsPerDomain": 3
}
```

# Actor output Schema

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

One item per discovered hostname, plus explicit status items for domains with no results or failed requests.

## `summary` (type: `string`):

Counts for requested, normalized, successful, empty, failed, discovered, saved, and truncated results.

# 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": [
        "similarweb.com"
    ],
    "includeApex": false,
    "maxResultsPerDomain": 3
};

// Run the Actor and wait for it to finish
const run = await client.actor("datascraperes/crt-name-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": ["similarweb.com"],
    "includeApex": False,
    "maxResultsPerDomain": 3,
}

# Run the Actor and wait for it to finish
run = client.actor("datascraperes/crt-name-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": [
    "similarweb.com"
  ],
  "includeApex": false,
  "maxResultsPerDomain": 3
}' |
apify call datascraperes/crt-name-subdomain-finder --silent --output-dataset

```

## MCP server setup

```json
{
    "mcpServers": {
        "apify": {
            "type": "http",
            "url": "https://mcp.apify.com/?tools=fetch-actor-details,datascraperes/crt-name-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/NXVmG3lXrjpFGZhcb/builds/VHETweF78tIPqTwdF/openapi.json