Filter hooks in Wordpress

Introduction

Filter hooks let you change data before WordPress uses it. They help you customize how things work without changing core files.

You want to change the text shown in a post title before it appears.

You need to modify a URL before WordPress outputs it.

You want to add extra HTML to content before it shows on the page.

You want to change a setting value dynamically without editing the original code.

Syntax

Wordpress

add_filter('hook_name', 'your_function_name', priority, accepted_args);

function your_function_name($value) {
    // change $value
    return $value;
}

add_filter connects your function to a filter hook.

Your function must return the changed value for WordPress to use it.

Examples

This adds 'Prefix: ' before every post title.

Wordpress

add_filter('the_title', 'add_prefix_to_title');

function add_prefix_to_title($title) {
    return 'Prefix: ' . $title;
}

This adds a thank you message at the end of every post content.

Wordpress

add_filter('the_content', 'add_footer_to_content', 10, 1);

function add_footer_to_content($content) {
    return $content . '<p>Thank you for reading!</p>';
}

Sample Program

This code changes the site tagline to 'My Custom Tagline' whenever WordPress gets the description info.

Wordpress

<?php
// Add a filter to change the site tagline
add_filter('bloginfo', 'change_tagline', 10, 2);

function change_tagline($output, $show) {
    if ($show === 'description') {
        return 'My Custom Tagline';
    }
    return $output;
}

// Usage example: echo get_bloginfo('description');

Important Notes

Always return the modified value in your filter function.

Use the correct hook name to target the data you want to change.

Priority controls the order if multiple filters use the same hook (lower runs first).

Summary

Filter hooks let you change data before WordPress uses it.

Use add_filter to connect your function to a filter hook.

Your function must return the changed value for WordPress to apply it.