Add ALTCHA Proof of Work to your Joomla form

ALTCHA is a privacy-friendly, self-hosted Proof of Work CAPTCHA that blocks spam bots without asking your visitors to click checkboxes or pick out traffic lights.

Rather than handing a puzzle to the person, ALTCHA hands the visitor's browser a small maths problem to work on quietly in the background. This is called a Proof of Work, or POW for short. A real visitor never notices it, but a bot firing off thousands of submissions pays the cost every single time, until spamming your form stops being worth the effort.

Everything happens between the browser and your own site: no API keys, no account, no third-party service, and no visitor data leaving your server. That also makes it the easiest captcha to set up in Convert Forms. Drop the field on your form, and you're done.

Add ALTCHA to your form

1. Go to Components → Convert Forms → Forms

   

2. Open the form you want to protect.

   

3. Choose the "Add Field" tab and click on the ALTCHA field in the Captcha Fields category.

   

The form now includes the ALTCHA (Proof of Work) captcha field.

Finally, save the form. Your form now includes the ALTCHA (Proof of work) captcha field.

What your visitors see

The widget sits in your form showing an "I'm not a robot" line with a spinner, and it starts solving the moment the page loads. By the time most people have finished typing their message, it's already verified. No clicking, no puzzles.

Translate the widget's text

To translate the ALTCHA widget's text, go to System → Manage → Language Overrides, select Site and your language, and create an override for each constant below.

Searching for the text won't find these constants, so type them in yourself.

Do you need Joomla's Proof of Work captcha plugin?

No. Joomla 6.1 ships its own Proof of Work captcha plugin, also built on ALTCHA, and you might already have it enabled for your site's login or registration forms.

Convert Forms doesn't use it. Our ALTCHA field is self-contained: it bundles its own widget, serves its own challenges, and verifies them itself. You don't have to enable Joomla's plugin, set it as your default captcha, or run Joomla 6.1 at all.

ALTCHA or one of the other captchas?

ALTCHA is the right default for most forms, especially if you'd rather not hand visitor data to Google or Cloudflare, or you just don't want to manage API keys.

Reach for one of the others when you need what they offer:

• Google reCAPTCHA and hCaptcha score visitor behaviour and can challenge suspicious ones.
• Cloudflare Turnstile is a good pick if your site already sits behind Cloudflare.
• Math Captcha asks the human to do the work, which some sites prefer.

You might not need a captcha at all

Convert Forms adds Honeypot protection to every form automatically. It's a hidden field that bots fill in, and humans never see, and it catches a lot of spam on its own.

If you're still getting through, stack ALTCHA on top of it and pair it with Minimum Time to Submit for good measure.