Technology Tales

Add Canonical Tags to WordPress without plugins

31^st March 2025

Search engines need to know which is which because they cannot know which is the real content when there is any duplication, unless you tell them. That is where canonical tags come in handy. By default, WordPress appears to add these for posts and pages, which makes sense. However, you can add them for other places too. While a plugin can do this for you, adding some code to your theme's functions.php file also does the job. This is how it could look:

function add_canonical_link() {
    global $post;

    // Check if we're on a single post/page
    if (is_singular()) {
        $canonical_url = get_permalink($post->ID);
    } 
    // For the homepage
    elseif (is_home() || is_front_page()) {
        $canonical_url = home_url('/');
    }
    // For category archives
    elseif (is_category()) {
        $canonical_url = get_category_link(get_query_var('cat'));
    }
    // For tag archives
    elseif (is_tag()) {
        $canonical_url = get_tag_link(get_query_var('tag_id'));
    }
    // For other archive pages
    elseif (is_archive()) {
        $canonical_url = get_permalink();
    }
    // Fallback for other pages
    else {
        $canonical_url = get_permalink();
    }

    // Output the canonical link
    echo '' . "\n";
}

// Hook the function to wp_head
add_action('wp_head', 'add_canonical_link');

// Remove default canonical link
remove_action('wp_head', 'rel_canonical');

The first part defines a function to define the canonical URL and create the tag to be added. With that completed, the penultimate piece of code hooks it into the wp_head part of the web page, while the last function gets rid of the default link to get avoid any duplication of output.