A simple and nice plugin to filter posts by their tags with ajax from sidebar widget. The plugin will make a Widget by ‘Iqlasit – Posts By Tags’ named into your widget panel. Just drag it to your sidebar then all of your tags will appear there. Now make a page and paste the shortcode [iqlasit_posts_by_tags]. When you’ll click on a tag the plugin will show the post that has the tag without loading the page.
Preview URL: https://wordpress.org/plugins/posts-by-tags/