Filters

the_content is the last chance to change post HTML before it reaches the template. Always return the string — filters that echo will break the page.

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Example

add_filter( 'the_content', function( $content ) {
    if ( is_single() ) {
        $content .= '<p><strong>Thanks for reading!</strong></p>';
    }
    return $content;
} );

Common Use Cases

• Append/prepend content to posts
• Transform shortcodes manually
• Add schema markup to content
• Strip or sanitize specific HTML

the_title changes how a title is displayed, not the value in the database. Guard with post ID so menus and admin lists are not rewritten by accident.

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Example

add_filter( 'the_title', function( $title, $id ) {
    if ( get_post_type( $id ) === 'book' ) {
        return 'Book: ' . $title;
    }
    return $title;
}, 10, 2 );

Common Use Cases

• Prefix/suffix titles by post type
• Truncate long titles
• Add icons or labels to titles
• Translate titles dynamically

wp_title is the classic document-title filter. Modern themes should prefer document_title_parts — this hook remains for older title tags.

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Example

add_filter( 'wp_title', function( $title, $sep ) {
    return $title . $sep . get_bloginfo( 'name' );
}, 10, 2 );

Common Use Cases

• Customize SEO page titles on legacy themes
• Append site name to titles
• Set title format for specific pages
• Override title for 404 pages

body_class lets CSS target context without extra wrappers. Return the array — do not echo class names.

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Example

add_filter( 'body_class', function( $classes ) {
    if ( is_user_logged_in() ) {
        $classes[] = 'user-logged-in';
    }
    return $classes;
} );

Common Use Cases

• Add role-based body classes
• Target specific page templates via CSS
• Add device detection classes
• Inject A/B test variant classes

excerpt_length only affects auto excerpts, not the Excerpt box in the editor. Return an integer word count.

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Example

add_filter( 'excerpt_length', function( $length ) {
    return 30;
} );

Common Use Cases

• Shorten excerpts for card layouts
• Lengthen excerpts for search results
• Vary length by post type
• Control reading time estimates

login_url is how membership and white-label sites hide wp-login.php. Return a full URL, not a path fragment.

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Example

add_filter( 'login_url', function( $url ) {
    return home_url( '/my-login/' );
} );

Common Use Cases

• Custom login page URL
• Hide wp-login.php from bots
• Membership site login flow
• White-label WordPress projects

the_excerpt filters the final excerpt string, whether it was typed manually or auto-generated — use excerpt_length/excerpt_more to shape the auto version instead.

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Example

add_filter( 'the_excerpt', function( $excerpt ) {
    return '<div class="excerpt-wrap">' . $excerpt . '</div>';
} );

Common Use Cases

• Wrap excerpts in custom markup
• Append a 'read more' link consistently
• Strip shortcodes left in excerpts

excerpt_more only changes the trailing string on auto-generated excerpts — it does nothing to a manually written excerpt.

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Example

add_filter( 'excerpt_more', function() {
    return ' <a href="' . get_permalink() . '">Read more →</a>';
} );

Common Use Cases

• Replace the ellipsis with a Read More link
• Localize the trailing string
• Add an icon after trimmed excerpts

post_class runs once per post inside the loop — unlike body_class, which runs once per page — so keep the callback fast if you're looping many posts.

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Example

add_filter( 'post_class', function( $classes, $css_class, $post_id ) {
    if ( has_post_thumbnail( $post_id ) ) {
        $classes[] = 'has-thumbnail';
    }
    return $classes;
}, 10, 3 );

Common Use Cases

• Add a class for featured-image presence
• Highlight sticky or featured posts
• Add taxonomy-term-based classes
• Alternate row classes for grid layouts

document_title_parts is the modern replacement for wp_title — it works with an array of parts, not a raw string, so you edit pieces instead of parsing text.

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Example

add_filter( 'document_title_parts', function( $title ) {
    if ( is_singular( 'book' ) ) {
        $title['title'] .= ' | Book Review';
    }
    return $title;
} );

Common Use Cases

• Customize SEO page titles per post type
• Remove the tagline/site name segment
• Add dynamic segments (category, search term)
• Override the title on 404 pages

wp_nav_menu_items lets you append or alter menu markup without editing the menu in the admin — useful for injecting a login/cart link at the end.

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Example

add_filter( 'wp_nav_menu_items', function( $items, $args ) {
    if ( 'primary' !== $args->theme_location ) {
        return $items;
    }
    $items .= is_user_logged_in()
        ? '<li><a href="' . wp_logout_url() . '">Log out</a></li>'
        : '<li><a href="' . wp_login_url() . '">Log in</a></li>';
    return $items;
}, 10, 2 );

Common Use Cases

• Append a login/cart/search item to a menu
• Inject a CTA button into navigation
• Conditionally add items by user role

wp_mail_from fixes the wordpress@yourdomain.com sender WordPress uses by default — pair it with wp_mail_from_name to fully brand outgoing mail.

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Example

add_filter( 'wp_mail_from', function() {
    return 'no-reply@example.com';
} );
add_filter( 'wp_mail_from_name', function() {
    return get_bloginfo( 'name' );
} );

Common Use Cases

• Fix deliverability by using a real domain address
• Brand transactional emails with the site name
• Route different email types from different addresses

upload_mimes controls what get_allowed_mime_types() and the uploader accept — adding a type here does not make it safe by itself; WordPress still runs its own file-content checks.

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Example

add_filter( 'upload_mimes', function( $mimes ) {
    $mimes['svg'] = 'image/svg+xml';
    return $mimes;
} );

Common Use Cases

• Allow SVG or other blocked file types
• Restrict uploads to a smaller set of types by role
• Add support for a niche file format

comment_text is where you'd add nofollow to links, auto-linkify text, or moderate content on display — it doesn't change what's stored in the database.

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Example

add_filter( 'comment_text', function( $comment_text, $comment ) {
    if ( $comment && ! $comment->user_id ) {
        $comment_text .= '<span class="guest-badge">Guest</span>';
    }
    return $comment_text;
}, 10, 2 );

Common Use Cases

• Add badges/labels to comment output
• Auto-link mentions or hashtags in comments
• Strip disallowed markup on display

template_include is the very last stop in the template hierarchy — return an absolute path to a PHP file and WordPress loads exactly that, bypassing the rest of the hierarchy.

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Example

add_filter( 'template_include', function( $template ) {
    if ( is_singular( 'book' ) ) {
        $custom = plugin_dir_path( __FILE__ ) . 'templates/single-book.php';
        if ( file_exists( $custom ) ) {
            return $custom;
        }
    }
    return $template;
} );

Common Use Cases

• Ship custom templates from a plugin
• Override a theme's template for a specific condition
• Serve a completely custom page (landing pages, builders)

admin_footer_text is a lightweight branding hook — agencies commonly use it to replace WordPress's default footer credit with their own support link.

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Example

add_filter( 'admin_footer_text', function() {
    return 'Managed by Acme Agency — <a href="https://example.com/support">Get support</a>';
} );

Common Use Cases

• White-label the admin footer for clients
• Add a support/help link
• Show the current plugin/theme version

script_loader_tag is how you add async/defer or a nonce to a specific enqueued script without touching the theme's enqueue logic wholesale.

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Example

add_filter( 'script_loader_tag', function( $tag, $handle ) {
    if ( 'my-script' !== $handle ) {
        return $tag;
    }
    return str_replace( ' src', ' defer src', $tag );
}, 10, 2 );

Common Use Cases

• Add async/defer to specific scripts
• Add a nonce or crossorigin attribute
• Remove type="text/javascript" for cleaner markup

render_block runs for every block on the page, core and custom alike — check $block['blockName'] or it will touch content you didn't intend to change.

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Example

add_filter( 'render_block', function( $block_content, $block ) {
    if ( 'core/image' !== $block['blockName'] ) {
        return $block_content;
    }
    return str_replace( '<img', '<img loading="lazy"', $block_content );
}, 10, 2 );

Common Use Cases

• Modify markup of one specific block type
• Inject wrapper markup around blocks
• Add tracking attributes to CTA blocks

rest_prepare_post lets you add or remove fields on the /wp/v2/posts response without touching register_rest_field — useful for last-mile shaping of what the API returns.

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Example

add_filter( 'rest_prepare_post', function( $response, $post ) {
    $response->data['reading_time'] = ceil( str_word_count( $post->post_content ) / 200 );
    return $response;
}, 10, 2 );

Common Use Cases

• Add computed/derived fields to the REST response
• Strip sensitive fields from public API output
• Reshape data for a headless front-end

wp_get_attachment_image_attributes touches every image WordPress renders through its own media functions — including inside blocks and thumbnails — so scope changes carefully.

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Example

add_filter( 'wp_get_attachment_image_attributes', function( $attr ) {
    $attr['loading'] = 'lazy';
    $attr['decoding'] = 'async';
    return $attr;
} );

Common Use Cases

• Add loading="lazy" or fetchpriority attributes
• Override alt text site-wide
• Add custom data-* attributes for a lightbox script

cron_schedules is the only way to add a custom recurring interval — WordPress ships with hourly, twicedaily, and daily only.

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Example

add_filter( 'cron_schedules', function( $schedules ) {
    $schedules['every_fifteen_minutes'] = [
        'interval' => 15 * MINUTE_IN_SECONDS,
        'display'  => 'Every 15 Minutes',
    ];
    return $schedules;
} );

Common Use Cases

• Add a custom recurring interval (e.g. every 15 minutes)
• Register a weekly or non-standard interval
• Match a plugin's own scheduled task frequency
• Support finer-grained sync/polling than core's daily/hourly options

authenticate is the chain that decides whether login credentials are valid — every auth method, from core's own password check to SSO plugins, hooks into this same filter.

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Example

add_filter( 'authenticate', function( $user, $username ) {
    if ( 'blocked_user' === $username ) {
        return new WP_Error( 'blocked', 'This account is disabled.' );
    }
    return $user;
}, 30, 3 );

Common Use Cases

• Add a second authentication factor before allowing login
• Block specific usernames or patterns
• Integrate an SSO/external identity provider
• Log failed or suspicious login attempts

rest_pre_dispatch lets you intercept a REST API request before WordPress even matches it to a route — the earliest point to block or fake a response.

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Example

add_filter( 'rest_pre_dispatch', function( $result, $server, $request ) {
    if ( str_starts_with( $request->get_route(), '/my-plugin/v1' ) && ! is_user_logged_in() ) {
        return new WP_Error( 'forbidden', 'Login required', [ 'status' => 401 ] );
    }
    return $result;
}, 10, 3 );

Common Use Cases

• Block REST API access globally or per-route before any processing
• Serve a cached response without running the real route logic
• Rate-limit or IP-block at the earliest possible point
• Mock or A/B test an endpoint's response

manage_posts_columns controls what shows up in wp-admin's post list table — add a custom column here, then fill it with manage_posts_custom_column.

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Example

add_filter( 'manage_posts_columns', function( $columns ) {
    $columns['word_count'] = 'Word Count';
    return $columns;
} );

Common Use Cases

• Show custom field values in the post list at a glance
• Remove default columns you don't need (Author, Comments)
• Control column display order
• Build a lightweight custom dashboard view