Core Web Vitals Fix Checklist for WordPress Sites (2026)

# Measure baseline CWV for your key pages
npx lighthouse https://your-wordpress-site.com \
  --output=json \
  --output-path=./baseline-home.json \
  --throttling-method=provided \
  --screenEmulation.mobile

# Extract key metrics
cat baseline-home.json | jq '{
  LCP: .audits["largest-contentful-paint"].numericValue,
  TBT: .audits["total-blocking-time"].numericValue,
  CLS: .audits["cumulative-layout-shift"].numericValue,
  Performance: .categories.performance.score
}'

# List all active plugins via WP-CLI
wp plugin list --status=active --fields=name,version,update

# Deactivate and test removal of suspect plugins
wp plugin deactivate plugin-slug
# Test site functionality → if nothing breaks, delete it
wp plugin delete plugin-slug

// wp-config.php — enable WordPress page caching
define('WP_CACHE', true);

// Recommended caching plugins (choose ONE):
// 1. WP Super Cache (free, simple, maintained by Automattic)
// 2. W3 Total Cache (free, advanced configuration)
// 3. WP Rocket (paid, best out-of-box configuration)
// 4. LiteSpeed Cache (free, if your host runs LiteSpeed server)

// functions.php — Preload the LCP image and set fetchpriority
function preload_lcp_image() {
    if (is_front_page()) {
        // Replace with your actual hero image path
        echo '<link rel="preload" href="' . get_template_directory_uri() .
             '/images/hero-banner.webp" as="image" type="image/webp" fetchpriority="high" />';
    }
}
add_action('wp_head', 'preload_lcp_image', 1);

// Disable lazy loading on the first image (likely the LCP element)
function disable_lazy_load_first_image($attr, $attachment, $size) {
    // WordPress 5.9+ lazy loads all images by default
    // Remove lazy loading from the first image on the page
    static $first_image = true;
    if ($first_image) {
        $attr['loading'] = 'eager';
        $attr['fetchpriority'] = 'high';
        $first_image = false;
    }
    return $attr;
}
add_filter('wp_get_attachment_image_attributes', 'disable_lazy_load_first_image', 10, 3);

# Option 1: Use ShortPixel plugin (auto-converts on upload)
wp plugin install shortpixel-image-optimiser --activate

# Option 2: Use Imagify plugin
wp plugin install imagify --activate

# Option 3: Server-side with .htaccess (no plugin needed)
# Requires mod_rewrite and WebP versions of all images

# .htaccess — Serve WebP images when browser supports them
<IfModule mod_rewrite.c>
    RewriteEngine On
    RewriteCond %{HTTP_ACCEPT} image/webp
    RewriteCond %{REQUEST_FILENAME} (.*)\.(jpe?g|png|gif)$
    RewriteCond %1.webp -f
    RewriteRule (.+)\.(jpe?g|png|gif)$ $1.webp [T=image/webp,L]
</IfModule>

<IfModule mod_headers.c>
    <FilesMatch "\.(jpe?g|png|gif)$">
        Header append Vary Accept
    </FilesMatch>
</IfModule>

// functions.php — defer all non-critical JS
function defer_non_critical_scripts($tag, $handle, $src) {
    // Don't defer jQuery core (many plugins depend on it inline)
    $no_defer = ['jquery-core', 'jquery-migrate', 'wp-polyfill'];
    if (in_array($handle, $no_defer)) {
        return $tag;
    }
    // Add defer attribute to all other scripts
    return str_replace(' src', ' defer src', $tag);
}
add_filter('script_loader_tag', 'defer_non_critical_scripts', 10, 3);

# Generate critical CSS for your key templates
npx critical https://your-site.com \
  --base ./ \
  --inline \
  --width 1300 \
  --height 900 \
  --css wp-content/themes/your-theme/style.css \
  > critical.css

// functions.php — Self-host Google Fonts instead of loading from CDN
function dequeue_google_fonts() {
    // Remove Google Fonts loaded by theme/plugins
    wp_dequeue_style('google-fonts');
    wp_deregister_style('google-fonts');
}
add_action('wp_enqueue_scripts', 'dequeue_google_fonts', 100);

// Enqueue self-hosted fonts with font-display: swap
function enqueue_local_fonts() {
    wp_enqueue_style(
        'local-fonts',
        get_template_directory_uri() . '/fonts/fonts.css',
        [],
        '1.0'
    );
}
add_action('wp_enqueue_scripts', 'enqueue_local_fonts');

/* fonts/fonts.css — Self-hosted with swap and size-adjust */
@font-face {
  font-family: 'Inter';
  src: url('inter-latin-400.woff2') format('woff2');
  font-display: swap;
  font-weight: 400;
  font-style: normal;
  unicode-range: U+0000-00FF, U+0131, U+0152-0153;
}

@font-face {
  font-family: 'Inter Fallback';
  src: local('Arial');
  size-adjust: 107.64%;
  ascent-override: 96.88%;
  descent-override: 24.15%;
  line-gap-override: 0%;
}

// functions.php — ensure all images have width/height
function add_image_dimensions($content) {
    // Find images without width/height attributes
    $content = preg_replace_callback(
        '/<img([^>]*)>/i',
        function ($matches) {
            $img = $matches[0];
            // Skip if width and height already present
            if (preg_match('/\bwidth\s*=/', $img) && preg_match('/\bheight\s*=/', $img)) {
                return $img;
            }
            // Extract src and get dimensions
            if (preg_match('/src=["\']([^"\']+)["\']/i', $img, $src_match)) {
                $image_path = str_replace(
                    site_url('/'),
                    ABSPATH,
                    $src_match[1]
                );
                if (file_exists($image_path)) {
                    $size = getimagesize($image_path);
                    if ($size) {
                        $img = str_replace(
                            '<img',
                            '<img width="' . $size[0] . '" height="' . $size[1] . '"',
                            $img
                        );
                    }
                }
            }
            return $img;
        },
        $content
    );
    return $content;
}
add_filter('the_content', 'add_image_dimensions');

// wp-config.php — limit revisions to reduce database bloat
define('WP_POST_REVISIONS', 5);
define('AUTOSAVE_INTERVAL', 120); // Autosave every 2 minutes instead of 60s

// Disable unused WordPress features that add JS/CSS
define('DISALLOW_FILE_EDIT', true); // Disable theme/plugin editor

# Clean up database (removes revisions, drafts, spam, transients)
wp post delete $(wp post list --post_type='revision' --format=ids) --force
wp transient delete --expired
wp db optimize

// functions.php — dequeue jQuery if not needed by active plugins
function remove_jquery_if_unnecessary() {
    if (!is_admin()) {
        wp_deregister_script('jquery');
        wp_deregister_script('jquery-migrate');
    }
}
add_action('wp_enqueue_scripts', 'remove_jquery_if_unnecessary');

// functions.php — add preconnect hints for third-party domains
function add_preconnect_hints() {
    // Only add if you actually load resources from these origins
    echo '<link rel="preconnect" href="https://fonts.googleapis.com" />';
    echo '<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />';
    // Add your CDN if applicable
    echo '<link rel="preconnect" href="https://cdn.your-domain.com" />';
}
add_action('wp_head', 'add_preconnect_hints', 1);

# .htaccess — aggressive browser caching for static assets
<IfModule mod_expires.c>
    ExpiresActive On
    ExpiresByType image/webp "access plus 1 year"
    ExpiresByType image/avif "access plus 1 year"
    ExpiresByType image/jpeg "access plus 1 year"
    ExpiresByType image/png "access plus 1 year"
    ExpiresByType image/svg+xml "access plus 1 year"
    ExpiresByType font/woff2 "access plus 1 year"
    ExpiresByType text/css "access plus 1 month"
    ExpiresByType application/javascript "access plus 1 month"
    ExpiresByType text/html "access plus 0 seconds"
</IfModule>

<IfModule mod_headers.c>
    <FilesMatch "\.(woff2|avif|webp|jpg|png|svg)$">
        Header set Cache-Control "public, max-age=31536000, immutable"
    </FilesMatch>
</IfModule>

# .htaccess — enable compression
<IfModule mod_deflate.c>
    AddOutputFilterByType DEFLATE text/html
    AddOutputFilterByType DEFLATE text/css
    AddOutputFilterByType DEFLATE application/javascript
    AddOutputFilterByType DEFLATE application/json
    AddOutputFilterByType DEFLATE image/svg+xml
    AddOutputFilterByType DEFLATE application/xml
    AddOutputFilterByType DEFLATE text/plain
</IfModule>

// functions.php — Add min-height to ad containers
function reserve_ad_space() {
    echo '<style>
        .ad-slot-leaderboard { min-height: 90px; contain: layout style; }
        .ad-slot-sidebar { min-height: 250px; contain: layout style; }
        .ad-slot-in-content { min-height: 250px; contain: layout style; }
    </style>';
}
add_action('wp_head', 'reserve_ad_space');

// wp-config.php — offload static assets to CDN
define('WP_CONTENT_URL', 'https://cdn.your-domain.com/wp-content');

// functions.php — remove emoji script (saves ~10KB per page)
remove_action('wp_head', 'print_emoji_detection_script', 7);
remove_action('wp_print_styles', 'print_emoji_styles');
remove_action('admin_print_scripts', 'print_emoji_detection_script');
remove_action('admin_print_styles', 'print_emoji_styles');

// functions.php — remove block library CSS if using classic editor
function remove_block_css() {
    wp_dequeue_style('wp-block-library');
    wp_dequeue_style('wp-block-library-theme');
    wp_dequeue_style('wc-blocks-style'); // WooCommerce blocks
    wp_dequeue_style('global-styles');
}
add_action('wp_enqueue_scripts', 'remove_block_css', 100);

// functions.php — reduce Heartbeat API polling frequency
function limit_heartbeat($settings) {
    $settings['interval'] = 60; // Default is 15 seconds
    return $settings;
}
add_filter('heartbeat_settings', 'limit_heartbeat');

// Disable Heartbeat on frontend entirely
function disable_frontend_heartbeat() {
    if (!is_admin()) {
        wp_deregister_script('heartbeat');
    }
}
add_action('init', 'disable_frontend_heartbeat', 1);

// functions.php — DNS prefetch for external resources
function add_dns_prefetch() {
    echo '<link rel="dns-prefetch" href="//www.google-analytics.com" />';
    echo '<link rel="dns-prefetch" href="//www.googletagmanager.com" />';
}
add_action('wp_head', 'add_dns_prefetch', 0);