WordPress hooks are a way to let developers extend, customize, or modify WordPress behavior without editing core files. Hooks are heavily used in WordPress core, themes, and plugins. WordPress has two main hook types: Actions and Filters.

What is a Hook?

A hook is a specific point in WordPress where custom code can run.

For example, you can use hooks to:

• Run code after a post is published
• Add custom CSS or JS in the header
• Modify email content before sending
• Add extra fields to a form
• Change plugin output

Types of WordPress Hooks

1. Action Hook

An action hook runs custom code at a specific time. It does not usually return a value. Actions are used when you want to “do something.” WordPress describes actions as hooks that run at specific points during execution.

Example

add_action('wp_head', 'nextcrm_add_custom_header_code');

function nextcrm_add_custom_header_code() {
    echo '<meta name="nextcrm" content="enabled">';
}

Here, the function runs inside the WordPress site header.

2. Filter Hook

A filter hook modifies data and returns the changed value. Filters are used when you want to “change something.” WordPress filters allow plugins to modify internal data at runtime.

Example

add_filter('the_content', 'nextcrm_add_text_after_content');

function nextcrm_add_text_after_content($content) {
    $content .= '<p>Thanks for reading.</p>';
    return $content;
}

Here, the post content is modified before displaying on the frontend.

Difference Between Action and Filter