How to Create a WordPress Search Form with Keyword and Custom Taxonomy Filters

If you're looking to enhance your WordPress search functionality, this guide shows you how to build a custom search form that filters by both keyword and custom taxonomy using a shortcode and the pre_get_posts hook.  

Step 1: Create the Custom Search Form with Shortcode

This shortcode renders a form with keyword input and a dropdown to select custom taxonomy terms.

function custom_search_form_shortcode() {
    ob_start();
    ?>
    <form role="search" method="get" class="search-form" action="<?php echo esc_url(home_url('/')); ?>">
        <div class="search-form-row">
            <label for="search-keyword">Search Keyword:</label>
            <input type="text" id="search-keyword" name="s" placeholder="Enter your keyword..." value="<?php echo get_search_query(); ?>" />
        </div>

        <div class="search-form-row">
            <label for="search-taxonomy">Filter by Custom Taxonomy:</label>
            <?php
            $taxonomy = 'your_custom_taxonomy'; // Change this to your taxonomy
            $terms = get_terms($taxonomy, array('hide_empty' => false));
            ?>
            <select name="custom_taxonomy" id="search-taxonomy">
                <option value="">All <?php echo $taxonomy; ?></option>
                <?php foreach ($terms as $term) : ?>
                    <option value="<?php echo esc_attr($term->slug); ?>" <?php selected($term->slug, get_query_var('custom_taxonomy')); ?>>
                        <?php echo esc_html($term->name); ?>
                    </option>
                <?php endforeach; ?>
            </select>
        </div>

        <div class="search-form-row">
            <button type="submit" class="search-submit">Search</button>
        </div>
    </form>
    <?php
    return ob_get_clean();
}
add_shortcode('custom_search_form', 'custom_search_form_shortcode');

Step 2: Modify the Main Query with pre_get_posts

Use pre_get_posts to make WordPress understand the new filter and keyword query:  

function custom_search_pre_get_posts($query) {
    if (is_admin() || !$query->is_main_query()) return;

    if ($query->is_search()) {
        if (!empty($_GET['s'])) {
            $query->set('s', sanitize_text_field($_GET['s']));
        }

        if (!empty($_GET['custom_taxonomy'])) {
            $query->set('tax_query', array(
                array(
                    'taxonomy' => 'your_custom_taxonomy',
                    'field' => 'slug',
                    'terms' => sanitize_text_field($_GET['custom_taxonomy']),
                ),
            ));
        }
    }
}
add_action('pre_get_posts', 'custom_search_pre_get_posts');

Step 3: Add Custom CSS to Style the Form

.search-form {
    display: flex;
    flex-wrap: wrap;
    margin-top: 20px;
}
.search-form-row {
    margin-bottom: 12px;
}
.search-form label {
    font-weight: bold;
    display: block;
    margin-bottom: 5px;
}
.search-form input[type="text"],
.search-form select {
    padding: 8px;
    width: 250px;
}
.search-form .search-submit {
    padding: 8px 20px;
    background-color: #0073aa;
    color: #fff;
    border: none;
    cursor: pointer;
}
.search-form .search-submit:hover {
    background-color: #005a88;
}

Step 4: Display the Search Form Using the Shortcode

To show the form anywhere (pages, posts, widgets), use the shortcode:

[custom_search_form]

  ⚠️ Remember to replace 'your_custom_taxonomy' with your actual taxonomy name in both form and query hook.  

Additional Resources

• Register Custom Taxonomy in WordPress
• Using pre_get_posts Hook
• WPBeginner Guide to Custom Search