Hooks in WordPress: What They Are and How to Use Them Effectively

WordPress hooks are a huge and essential topic in WordPress development, acting as the core system for extending and customizing WordPress. We are going to have a bird’s-eye view on how they work and what we can achieve with them in this post. For a more thorough guide you can check WordPress documentation.

What Are Hooks in WordPress?

Ηooks allow you to customize WordPress’ behavior without altering the original code since they don’t modify core files. This way updates won’t wipe out your custom code.

By mastering hooks, you can understand how WordPress truly operates internally.

WordPress hooks come in two main types.

Action hooks and filter hooks each play a unique role, but both give you the power to extend WordPress functionality. Actions enable you to perform an action at set points during WordPress’s run, while filters let you modify and return data.

Action Hooks: Enabling Functionality

Action hooks let you execute custom code at specific moments during WordPress’s loading process. Think of them as checkpoints where WordPress pauses and asks, “Does anyone want to do something here?”

You can inject your own functions at these checkpoints to add features, modify behavior, or trigger events.

Activating the add_action() function is necessary to add an action hook. Register the hooks within your child theme’s function.php.

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What’s Going On Here?

• add_action() is hooking our custom function, $the_callback, into the $the_hook hook.
• $priority is the priority, defining when (before or after) the action will run compared to other hooked functions if any. The default priority is 10.
• The last parameter ($accepted_args) tells WordPress how many arguments our custom callback expects with the default being one (1). This is usefule in cases where developers fire custom action hooks, and in those cases, you’d absolutely need to define how many arguments your function expects.
  

Note: Even though in cases like wp_footer, the action function doesn't pass any arguments by default, this setup doesn’t break anything.

Note: You can register hooks inside your parent theme’s function.php file , but it’s not considered good practice since all this code will be overwritten every time a WP update takes place.

Some very useful hooks are wp_head and wp_footer.

The wp_head hook fires right before WordPress closes the </head> tag in your HTML, making it perfect for adding custom CSS, analytics tracking, or meta tags.

At the same time, wp_footer runs just before the closing </body> tag, making it ideal for scripts that should load after your content.

These two hooks handle a massive percentage of Theme and Plugin customizations because they catch your site at crucial moments in the page-building process.

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Filter Hooks: Changing What Already Exists

While action hooks let you add new functionality, filter hooks modify existing data before WordPress displays it. They review, change, and then forward content.

A filter hook can be created by using the add_filter() function.

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The filter hook updates an existing value.

This is a sample filter hook to include in functions.php.

We’ll take a closer look at the code:

• the_title is used to filter the post title before it is displayed on screen.
• add_emoji_to_title_frontend is the actuall callback we use to modify the title. It uses two arguments ($title, $post_id). The second, although not necessary in this code, makes it more flexible.
  • is_admin() ensures the filter doesn’t run on the dashboard
  • in_the_loop() ensures the filter only runs during the main post loop
  • is_main_query() ensures it doesn’t run inside sidebars or menus
• $priority is used in filters exactly as it’s used in actions, with 10 being the default priority number.
• $accepted_args is also used in filters. We set it to 2 since we use two arguments in our callback.

Adding this filter to functions.php will enrich all post titles with a beutiful emoji!

Filters typically focus on modifying output—text, HTML, URLs, or any data WordPress plans to display.

WordPress has many predefined filters that allow developers to add their own code at specific points throughout the WordPress core.

The WordPress Plugin API gives a comprehensive list of filter hooks available for use.

Implementing custom hooks using do_action in WordPress.

Adding custom hooks in WordPress is a powerful way to make your theme or plugin extensible for yourself or other developers.

A custom hook is a placeholder you define in your code—using do_action()—where other developers (or you later) can insert custom functionality without modifying the original code.

How to Add a Custom Action Hook

You use do_action( ‘your_custom_hook_name’ ) wherever you want the hook to fire.

Example: A Custom Hook in a Theme Footer

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Now, any plugin or theme can hook into my_custom_footer_hook like this:

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Implementing custom filters using apply_filter in WordPress

You’d only use apply_filters() if you’re building your own plugin or a child theme and want to let other developers customize your code

Let’s say you want to display a dynamic greeting on your WordPress site — but you’d like it to be customizable by other developers.

That’s a perfect use case for a custom filter.

Step 1: Define and Apply Your Custom Filter

Inside your theme or plugin (for example, functions.php or a custom plugin file):

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What happens here:

• You define a base value ("Hello").
• You call apply_filters( 'custom_greeting_text', $greeting, $user_name );
• That gives other code a chance to change $greeting before it’s used.
• The modified (or unchanged) greeting is returned.

Step 2: Hook Into the Custom Filter

Let’s say another developer (or you later) wants to change that greeting without editing your original code.
They can hook into the custom filter like this:

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Step 3: Use the Function Somewhere

Now, when the same line runs:

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Wrapping Up

WordPress hooks matter because they enable customization, add new functionality, and improve compatibility without modifying core files, making themes and plugins extensible.

Every plugin you install uses hooks to integrate with WordPress. Themes use hooks extensively too—that’s how child themes can modify parent theme behavior without editing the original files.

Understanding hooks transforms you from someone who just installs plugins to someone who can customize those plugins or build entirely new functionality. You’re no longer limited to what’s available in the plugin repository—you can make WordPress do exactly what your project needs.

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