Set Minimum Comment Length in WordPress

If you do not want short comments on your posts such as “Thanks!” or “Great article…“, add the following code to your functions.php file and set the minimum character count on line 4:

function minimal_comment_length( $commentdata ) {
    $minimalCommentLength = 20;
    if ( strlen( trim( $commentdata['comment_content'] ) ) < $minimalCommentLength ) {

        wp_die( 'Your comment must contain at least ' . $minimalCommentLength . ' characters.' );

    }

    return $commentdata;
}
add_filter( 'preprocess_comment', 'minimal_comment_length' );

For more comment management, see Show the Total Number of Comments.