Can't recommend

I’m glad I decided to look at the code. First off, it doesn’t support custom post types. Second, it directly alters (i.e. ALTER TABLE) the wp_posts table in the database, rather that using the wp_postmeta table to store the user’s selection. It also stored the selection on wp_insert_post, rather than save_post, so it would only run on new posts, and not when a post is updated. In other words, you could never change the setting.

I give it 2 stars because it will work for most people, but only 2 stars because of how it works and that it doesn’t meet my needs.

I’m not sure the best way to make these modifications available..? I can put the zip file up somewhere. They are posted below. Should be easy to see where I made changes.

<?php
/*
Plugin Name: WordPress Meta Robots
Plugin URI: https://www.typomedia.org/wordpress/plugins/wordpress-meta-robots/
Description: This plugin will give you full control of the <code>meta robots</code> tag for each post or page.
Author: Typomedia Foundation
Version: 2.0
Author URI: https://www.typomedia.org/
*/

if ( !class_exists ('wp_meta_robots_plugin')) {
	class wp_meta_robots_plugin {

	/* mod BL 2013.07.17: shouldn't alter built-in WordPress tables */
	/*function meta_robots_addcolumn() {
		global $wpdb;
		if (false === $wpdb->query("SELECT meta_robots FROM $wpdb->posts LIMIT 0")) {
			$wpdb->query("ALTER TABLE $wpdb->posts ADD COLUMN meta_robots varchar(20)");
		}
	}*/
	/* mod-end */

	/* mod BL 2013.07.17: Adding to wp_postmeta instead, and in response to save_post, also sanitizing inputs and checking nonce */
	/*function meta_robots_insert_post($pID) {
		global $wpdb;
		extract($_POST);
		$wpdb->query("UPDATE $wpdb->posts SET meta_robots = '$meta_robots' WHERE ID = $pID");
	}*/
	function meta_robots_save_post($post_id) {
		global $wpdb;

		// verify this came from the our screen and with proper authorization,
		// because save_post can be triggered at other times
		if ( !isset($_POST['meta_robots_metabox_noncename'])
				|| !wp_verify_nonce($_POST['meta_robots_metabox_noncename'], plugin_basename(__FILE__)) ) {
			return $post_id;
		}

		// verify if this is an auto save routine. If it is our form has not been submitted, so we dont want
		// to do anything
		if ( defined('DOING_AUTOSAVE') && DOING_AUTOSAVE )
			return $post_id;

		// Check permissions
		if ('page' == $_POST['post_type'] ) {
			if ( !current_user_can('edit_page', $post_id) )
				return $post_id;
		} else {
			if ( !current_user_can('edit_post', $post_id) )
				return $post_id;
		}

		// if this is a revision, get the original post_id
		if ( ($temp = wp_is_post_revision($post_id)) !== false )
			$post_id = $temp;

		// validate & save fields
		$acceptable_values = array('index, follow', 'index, nofollow', 'noindex, follow', 'noindex, nofollow');
		$meta_robots = $acceptable_values[0];
		if ( isset($_POST['meta_robots']) ) {
			$meta_robots = filter_var($_POST['meta_robots'], FILTER_SANITIZE_STRING);
			if ( !in_array($meta_robots, $acceptable_values) )
				$meta_robots = $acceptable_values[0];
		}

		// if there are no selections, attempt to delete the meta info
		if ( empty($meta_robots) )
			delete_post_meta($post_id, 'meta_robots');
		else if ( !add_post_meta($post_id, 'meta_robots', $meta_robots, true) )
			update_post_meta($post_id, 'meta_robots', $meta_robots);

		// done
		return $post_id;

	}
	/* mod-end */

	function meta_robots_options_box() {
		add_meta_box('meta_robots', 'Meta Robots', array('wp_meta_robots_plugin','meta_robots_dropdown_box'), 'page', 'side', 'low');
		add_meta_box('meta_robots', 'Meta Robots', array('wp_meta_robots_plugin','meta_robots_dropdown_box'), 'post', 'side', 'low');
		/* mod BL 2013.07.17: adding support for custom post types */
		$post_types = get_post_types(array('public' => true,'_builtin' => false), 'names');
		foreach ( $post_types as $post_type ) {
			add_meta_box('meta_robots', 'Meta Robots', array('wp_meta_robots_plugin','meta_robots_dropdown_box'), $post_type, 'side', 'low');
		}
		/* mod-end */
	}

	function meta_robots_dropdown_box() {
		global $post;
		/* mod BL 2013.07.17: switching to post meta, and adding a nonce */
		//$meta_robots = $post->meta_robots;
		$meta_robots = get_post_meta($post->ID, 'meta_robots', true);
		wp_nonce_field(plugin_basename(__FILE__), 'meta_robots_metabox_noncename');
		/* mod-end */
	?>
		<fieldset id="mycustom-div">
		<div>
		<p>
		<label for="meta_robots" ></label>
		<select name="meta_robots" id="meta_robots">
		<option <?php if ($meta_robots == "index, follow") echo 'selected="selected"';?>>index, follow</option>
		<option <?php if ($meta_robots == "index, nofollow") echo 'selected="selected"';?>>index, nofollow</option>
		<option <?php if ($meta_robots == "noindex, follow") echo 'selected="selected"';?>>noindex, follow</option>
		<option <?php if ($meta_robots == "noindex, nofollow") echo 'selected="selected"';?>>noindex, nofollow</option>
		</select>
		</p>
		</div>
		</fieldset>
	<?php
	}

	function add_meta_robots_tag() {
		global $post;
		/* mod BL 2013.07.17: switching to post meta, and cleaning up code for my own benefit */
		$meta_robots = get_post_meta($post->ID, 'meta_robots', true);
		if ( is_home() || is_single() || is_page() ) {
			echo '<meta name="robots" content="'.(empty($meta_robots) ? 'index, follow' : $meta_robots).'" />'."\n";
		} elseif ( is_category() || is_tag() || is_archive() ) {
			echo '<meta name="robots" content="noindex, follow" />'."\n";
		} else {
			echo '<meta name="robots" content="noindex, nofollow" />'."\n";
		}
		/* mod-end */
	}

	} // class meta_robots_plugin
}

/* mod BL 2013.07.17: shouldn't alter built-in WordPress tables */
//add_action('init', array('wp_meta_robots_plugin','meta_robots_addcolumn'));
/* mod-end */
add_action('admin_menu', array('wp_meta_robots_plugin','meta_robots_options_box'));
/* mod BL 2013.07.17: this should be called on save_post so the user can change it. */
//add_action('wp_insert_post', array('wp_meta_robots_plugin','meta_robots_insert_post'));
add_action('save_post', array('wp_meta_robots_plugin','meta_robots_save_post'));
/* mod-end */
add_action('wp_head', array('wp_meta_robots_plugin','add_meta_robots_tag'));
?>