Guards

Uniform offers several mechanisms for spam protection. Similar to actions, guards can be extended and combined. To add custom guards, create a site/plugins/uniform-guards/uniform-guards.php file and implement all your custom guards there. Take a look at the calc guard to see how to implement one.

Honeypot

The honeypot guard will reject all requests where a special (visually hidden) form field was filled out. The default name of the honeypot field is website to attract the attention of the bots. With the honeypot option you can change the default name to whatever you like but you should try to make it sound interesting for the bots. Example:

uniform('contact-form', [
   'honeypot' => 'fill-me',
   'actions' => [
      // ...
   ]
]);
//...
<input type="text" name="fill-me" id="fill-me" class="uniform__potty" />

The honeypot guard is activated in the default setup of Uniform.

Calc

The calc guard will reject all requests where a simple arithmetic problem is not solved correctly. You can set it up like this:

uniform('contact-form', [
   'guard' => 'calc',
   'actions' => [
      // ...
   ]
]);
//...
<label for="_captcha" class="required">Please calculate <?php echo uniform_captcha($form) ?></label>
<input<?php e($form->hasError('_captcha'), ' class="erroneous"')?> type="number" name="_captcha" id="_captcha" required/>

The uniform_captcha() function will generate a new arithmetic problem for the form and store the correct result in a session variable each time it is called.

reCAPTCHA

Head over to the repository of the reCAPTCHA guard for the documentation. Thanks @fetzi!