{"slug":"wordpress-hooks-actions-filters","title":"WordPress Actions and Filters (Hook System)","tags":["hooks","actions","filters","functions.php","php"],"agent_summary":"WordPress hook system: add_action and add_filter syntax, priority and argument count, remove_action and remove_filter, common hook names (wp_head, save_post, pre_get_posts), and creating custom hooks with do_action and apply_filters.","trigger_phrases":["wordpress hooks","add_action wordpress","add_filter wordpress","functions.php hooks","wordpress actions filters","do_action custom","apply_filters custom","wp_head hook"],"runnable":true,"markdown":"\nWordPress's hook system allows modifying behavior without editing core files. Actions DO things; filters TRANSFORM values.\n\n## Actions\n\n```php\n// Basic action\nadd_action('wp_head', 'add_custom_analytics');\nfunction add_custom_analytics() {\n echo '';\n}\n\n// Remove a core action\nremove_action('wp_head', 'wp_generator');\n\n// Action with priority (lower = earlier) and argument count\nadd_action('save_post', 'on_post_save', 10, 2);\nfunction on_post_save($post_id, $post) {\n if ($post->post_type !== 'service') return;\n // Clear cache, ping API, etc.\n}\n```\n\n### Common Action Hooks\n\n| Hook | Fires When |\n|------|-----------|\n| `init` | Early initialization — register CPTs, taxonomies |\n| `wp_enqueue_scripts` | Enqueue frontend scripts/styles |\n| `admin_enqueue_scripts` | Enqueue admin scripts/styles |\n| `wp_head` | Output to `` |\n| `wp_footer` | Output before `` |\n| `save_post` | After post saved to DB |\n| `template_redirect` | Before template loads — redirect logic |\n| `widgets_init` | Register sidebars and widgets |\n| `after_setup_theme` | Theme features (add_theme_support) |\n\n## Filters\n\n```php\n// Append CTA to single post content\nadd_filter('the_content', 'append_cta_to_posts');\nfunction append_cta_to_posts($content) {\n if (!is_single()) return $content;\n return $content . '

';\n}\n\n// Modify excerpt length (default 55 words)\nadd_filter('excerpt_length', function() { return 30; });\n\n// Change wp_mail sender name\nadd_filter('wp_mail_from_name', function() { return 'My Company'; });\n\n// Modify login redirect by role\nadd_filter('login_redirect', function($url, $request, $user) {\n if (isset($user->roles) && in_array('editor', $user->roles)) {\n return admin_url('edit.php');\n }\n return $url;\n}, 10, 3);\n```\n\n### Common Filter Hooks\n\n| Hook | What It Filters |\n|------|----------------|\n| `the_content` | Post body before display |\n| `the_title` | Post title before display |\n| `excerpt_length` | Auto-excerpt word count |\n| `upload_mimes` | Allowed upload file types |\n| `pre_get_posts` | WP_Query before DB — modify main query |\n| `wp_mail_from` | From email address |\n| `login_redirect` | Post-login redirect URL |\n\n## Custom Hooks\n\n```php\n// Define in plugin/theme — lets third-party code hook in\ndo_action('myplugin_after_lead_saved', $lead_id, $lead_data);\n$price = apply_filters('myplugin_service_price', $base_price, $service_id);\n\n// Third-party hooks in\nadd_action('myplugin_after_lead_saved', 'send_lead_to_crm', 10, 2);\nadd_filter('myplugin_service_price', 'apply_member_discount', 10, 2);\n```\n\n## Priority Rules\n\n- Default priority: 10\n- Lower number = fires earlier\n- Same priority + same hook = fires in order added\n- `remove_action` / `remove_filter` must match the exact priority used when adding\n","html":"

WordPress's hook system allows modifying behavior without editing core files. Actions DO things; filters TRANSFORM values.

Actions

// Basic action\nadd_action('wp_head', 'add_custom_analytics');\nfunction add_custom_analytics() {\n    echo '<script>/* GA4 snippet */</script>';\n}\n\n// Remove a core action\nremove_action('wp_head', 'wp_generator');\n\n// Action with priority (lower = earlier) and argument count\nadd_action('save_post', 'on_post_save', 10, 2);\nfunction on_post_save($post_id, $post) {\n    if ($post->post_type !== 'service') return;\n    // Clear cache, ping API, etc.\n}\n

Common Action Hooks

| Hook | Fires When |\n|------|-----------|\n| init | Early initialization — register CPTs, taxonomies |\n| wp_enqueue_scripts | Enqueue frontend scripts/styles |\n| admin_enqueue_scripts | Enqueue admin scripts/styles |\n| wp_head | Output to <head> |\n| wp_footer | Output before </body> |\n| save_post | After post saved to DB |\n| template_redirect | Before template loads — redirect logic |\n| widgets_init | Register sidebars and widgets |\n| after_setup_theme | Theme features (add_theme_support) |

Filters

// Append CTA to single post content\nadd_filter('the_content', 'append_cta_to_posts');\nfunction append_cta_to_posts($content) {\n    if (!is_single()) return $content;\n    return $content . '<div class=\"cta-box\"><a href=\"/contact/\">Get a Free Quote</a></div>';\n}\n\n// Modify excerpt length (default 55 words)\nadd_filter('excerpt_length', function() { return 30; });\n\n// Change wp_mail sender name\nadd_filter('wp_mail_from_name', function() { return 'My Company'; });\n\n// Modify login redirect by role\nadd_filter('login_redirect', function($url, $request, $user) {\n    if (isset($user->roles) && in_array('editor', $user->roles)) {\n        return admin_url('edit.php');\n    }\n    return $url;\n}, 10, 3);\n

Common Filter Hooks

| Hook | What It Filters |\n|------|----------------|\n| the_content | Post body before display |\n| the_title | Post title before display |\n| excerpt_length | Auto-excerpt word count |\n| upload_mimes | Allowed upload file types |\n| pre_get_posts | WP_Query before DB — modify main query |\n| wp_mail_from | From email address |\n| login_redirect | Post-login redirect URL |

Custom Hooks

// Define in plugin/theme — lets third-party code hook in\ndo_action('myplugin_after_lead_saved', $lead_id, $lead_data);\n$price = apply_filters('myplugin_service_price', $base_price, $service_id);\n\n// Third-party hooks in\nadd_action('myplugin_after_lead_saved', 'send_lead_to_crm', 10, 2);\nadd_filter('myplugin_service_price', 'apply_member_discount', 10, 2);\n

Priority Rules

Default priority: 10
Lower number = fires earlier
Same priority + same hook = fires in order added
remove_action / remove_filter must match the exact priority used when adding

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