Adding custom PHP code to WordPress unlocks endless possibilities for customization. Whether you want to display notifications, modify functionality, or integrate third-party tools, PHP is your go-to language. However, inserting code incorrectly can break your site.
In this guide, you’ll learn three safe methods to add PHP code to WordPress, including how to display a header notification. Let’s dive in!

Method 1: Add PHP Code via Child Theme’s functions.php

This method is perfect for theme-specific tweaks

Step 1: Create a Child Theme (Essential!)

Editing a parent theme directly risks losing changes during updates. Create a child theme first.
Follow this step-by-step tutorial to set one up.

Step 2: Insert PHP Code into functions.php

1. Go to Appearance > Theme Editor . (In Block Themes, go to Tools > Theme File Editor.)
2. Select your child theme.
3. Open the functions.php file.
4. Add this code to display a notification in the header:

function my_header_notification() {
    echo '<div style="background:#f00; color:#fff; padding:10px; text-align:center;">Welcome to Our Site!</div>';
}
add_action('wp_head', 'my_header_notification');

This displays a notification in your site’s header.

Pros:

• Safe for theme updates.
• Ideal for theme-dependent code.

Cons:

• Code won’t work if you switch themes.

Method 2: Using a Custom Plugin

This method is Ideal for developers or long-term solutions. Plugins isolate functionality from themes, making them ideal for reusable features.

Build a Basic Plugin

1. Access your site via FTP/cPanel.
2. Navigate to /wp-content/plugins/.
3. Create a folder: my-plugin.
4. Inside it, create my-plugin.php with this header:

<?php
/*
Plugin Name: My plugin
Description: Adds my custom codes to WordPress.
Version: 1.0
Author: Your Name
*/

// Load notification code
require_once plugin_dir_path(__FILE__) . 'includes/header-notification.php';

5. Create an includes folder and add header-notification.php:

<?php
function my_header_notification() {
    echo '<div style="background:#0f0; color:#000; padding:10px; text-align:center;">Thanks for visiting our site!</div>';
}
add_action('wp_head', 'my_header_notification');

6. Activate the plugin in Plugins > Installed Plugins .

Here, we created a separate file for the notification code and included it in the main plugin file.
The advantage of this method is that you can create a separate file for each of your codes and include them in the main plugin file, which makes managing these codes very easy.

Pros:

• Independent of themes.
• Modular architecture simplifies updates and debugging.
• Portability: Can be easily deactivated and reactivated without affecting the theme.

Cons:

• Requires manual plugin setup.
• Overkill for small tweaks.

Method 3: Use a Helper Plugin (Code Snippets/FluentSnippets)

Perfect for non-developers! Plugins like Code Snippets simplify adding code without touching files.

Using Code Snippets

Step 1: Install Code Snippets

1. Go to Plugins > Add New.
2. Search for “Code Snippets”, install, and activate it.

Step 2: Add Your PHP Code

1. Go to Snippets > Add New.
2. Title it (e.g., “Header Notification”).
3. Paste your code:

function my_header_notification() {
    echo '<div style="background:#0f0; color:#000; padding:10px; text-align:center;">Thanks for visiting our site!</div>';
}
add_action('wp_head', 'my_header_notification');

4. Under Settings, set the hook to Run snippet everywhere.
5. Save and activate.

Using FluentSnippets

FluentSnippets offers enhanced security and performance through file-based snippet storage:

1. Install FluentSnippets from the plugin directory.
2. Go to FluentSnippets > Add New Snippet.
3. Paste the same code as above and configure conditions (e.g., display on specific pages).

Pros:

• No coding skills required.
• Snippets are easy to manage.

Cons:

• Relies on third-party plugin security.
• Too many snippets may slow your site.

Choosing the Right Method

The best method depends on your specific needs and technical comfort level:

• Child Theme: if you’re already using a child theme and want to keep your customizations theme-specific.
• Custom Plugin: if you want your code to be portable and reusable across different themes or sites.
• Helper Plugin: if you prefer a user-friendly interface and want to avoid directly editing theme files or creating plugins.

For most users, helper plugins like Code Snippets provide the safest and quickest way to inject PHP code, especially for one-off modifications. 
Child themes remain ideal for theme-specific customizations, while custom plugins suit complex, reusable functionality.

If this article is difficult for you to read in text, you can watch the video version below.