Altcha

Altcha is an open-source, privacy-first CAPTCHA alternative that uses proof-of-work challenges to verify human users without tracking or fingerprinting. It is increasingly adopted by privacy-conscious applications and is designed to be GDPR-compliant by default. The challenge requires computing a cryptographic proof that is submitted as a token with form data.

Supported Types

Type	Proxy Required	Description
AltchaToken	Yes	Solves the challenge using your proxy.
AltchaTokenProxyLess	No	Solves the challenge without a proxy. Recommended for most use cases.

Parameters

Parameter	Type	Required	Description
type	string	Yes	AltchaToken or AltchaTokenProxyLess
websiteURL	string	Yes	The URL of the page containing the Altcha widget
websiteKey	string	Yes	The site key or challenge URL found in the Altcha widget configuration

Proxy Parameters

Required when using the AltchaToken type:

Parameter	Type	Required	Description
proxyType	string	Yes	http, socks4, or socks5
proxyAddress	string	Yes	Proxy IP or hostname
proxyPort	integer	Yes	Proxy port
proxyLogin	string	No	Proxy username
proxyPassword	string	No	Proxy password

Create Task Request

{
  "clientKey": "YOUR_API_KEY",
  "task": {
    "type": "AltchaTokenProxyLess",
    "websiteURL": "https://example.com/contact",
    "websiteKey": "ckey_2JDa7N9bR..."
  }
}

With proxy:

{
  "clientKey": "YOUR_API_KEY",
  "task": {
    "type": "AltchaToken",
    "websiteURL": "https://example.com/contact",
    "websiteKey": "ckey_2JDa7N9bR...",
    "proxyType": "http",
    "proxyAddress": "1.2.3.4",
    "proxyPort": 8080,
    "proxyLogin": "user",
    "proxyPassword": "pass"
  }
}

Response

{
  "errorId": 0,
  "taskId": "550e8400-e29b-41d4-a716-446655440000",
  "status": "processing"
}

Solution Object

{
  "token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..."
}

Field	Type	Description
token	string	The proof-of-work solution token to submit with the form

How to Use

1. Find the Altcha widget on the target page. The site key is typically in the widget element’s data-altcha-key attribute or in the JavaScript initialization code.
2. Submit the task and poll for the solution.
3. Set the returned token as the value of the Altcha hidden input field in the form (usually named altcha).
4. Submit the form. The server will verify the proof-of-work token.

Note

Altcha tokens are typically short-lived. Use the token promptly after receiving it to avoid expiration.

Code Examples

Python

import requests
import time

API_KEY = "YOUR_API_KEY"

response = requests.post("https://api.ucaptcha.net/createTask", json={
    "clientKey": API_KEY,
    "task": {
        "type": "AltchaTokenProxyLess",
        "websiteURL": "https://example.com/contact",
        "websiteKey": "ckey_2JDa7N9bR..."
    }
})
task_id = response.json()["taskId"]

while True:
    result = requests.post("https://api.ucaptcha.net/getTaskResult", json={
        "clientKey": API_KEY,
        "taskId": task_id
    }).json()
    if result["status"] == "ready":
        token = result["solution"]["token"]
        print("Solution:", token)

        # Submit the form with the Altcha token
        form_data = {
            "altcha": token,
            "name": "John",
            "message": "Hello"
        }
        response = requests.post("https://example.com/contact", data=form_data)
        print("Status:", response.status_code)
        break
    elif result["status"] == "failed":
        print("Error:", result.get("errorDescription"))
        break
    time.sleep(5)

JavaScript

const API_KEY = "YOUR_API_KEY";

const { taskId } = await fetch("https://api.ucaptcha.net/createTask", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    clientKey: API_KEY,
    task: {
      type: "AltchaTokenProxyLess",
      websiteURL: "https://example.com/contact",
      websiteKey: "ckey_2JDa7N9bR..."
    }
  })
}).then(r => r.json());

while (true) {
  const result = await fetch("https://api.ucaptcha.net/getTaskResult", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({ clientKey: API_KEY, taskId })
  }).then(r => r.json());

  if (result.status === "ready") {
    console.log("Solution:", result.solution.token);
    break;
  } else if (result.status === "failed") {
    console.error("Error:", result.errorDescription);
    break;
  }
  await new Promise(r => setTimeout(r, 5000));
}

cURL

# Create the task
curl -X POST https://api.ucaptcha.net/createTask \
  -H "Content-Type: application/json" \
  -d '{
    "clientKey": "YOUR_API_KEY",
    "task": {
      "type": "AltchaTokenProxyLess",
      "websiteURL": "https://example.com/contact",
      "websiteKey": "ckey_2JDa7N9bR..."
    }
  }'

# Poll for the result (replace TASK_ID with the returned taskId)
curl -X POST https://api.ucaptcha.net/getTaskResult \
  -H "Content-Type: application/json" \
  -d '{
    "clientKey": "YOUR_API_KEY",
    "taskId": "TASK_ID"
  }'

Provider Coverage

• 2Captcha
• Anti-Captcha
• CapMonster

Aliases

No backward-compatible aliases. Use AltchaToken or AltchaTokenProxyLess directly.