Chetan Vaghela

The plugin provides a funcationality to add validation on WordPress default comment form using Javascript and prevents it from dying when an error occurs and user can prevent to die on duplicate comment message.
<h3>Features And Options:</h3>
<ul>
<li>Validation on required fields using javascript.</li>
<li>prevent to die on comment form error message.</li>
<li>On duplicate comment display message below comment form instead die.</li>
<li>Change Comment form submit button text</li>
</ul>

Comment form validation and Customization

Wordpress default comment form validation using javascript and customization.

WP Sites - Brad Dalton

Note: Requires WordPress 3.6 or higher
This plugin simply removes:
<ol>
<li>The Website URL Field From All Comment Forms.</li>
<li>ALL Comment Form Allowed Tags Which Attract Automated Comment Form Spam.</li>
<li>The ‘Your email address will not be published’ text which also attracts comment form bots because it includes the text ’email’.</li>
</ol>
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Stop Comment Form Spam

New WordPress 3.6 or higher plugin which removes the website url field and comment form allowed tags which attract automated comment spam.

Comment form validation and Customization vs Stop Comment Form Spam