WordPress plugin development extends core functionality without modifying WordPress files. Professional plugin development follows established patterns ensuring security, performance, and compatibility. London developers require plugin development skills creating custom solutions for unique business requirements beyond available commercial plugins.
WordPress plugins are PHP packages adding functionality to WordPress installations. Plugins leverage WordPress APIs, hooks, and filters integrating seamlessly without core modifications.
Plugins range from simple modifications adding single features to complex applications transforming WordPress capabilities. Well-architected plugins feel like native WordPress features.
Plugin architecture enables WordPress remaining lightweight. Core provides essential features; plugins add specialised functionality as needed.
Professional plugin development requires understanding WordPress APIs, security best practices, and coding standards. Poor plugins create vulnerabilities, performance issues, and conflicts.
Plugin development enables monetisation through premium plugins or freelance custom development enhancing WordPress development careers.
WordPress plugins require minimum code creating functional extensions. Simple plugins need single PHP file; complex plugins use organised directory structures.
Minimum Plugin File:
<?php
/**
* Plugin Name: Custom Plugin Name
* Plugin URI: https://londonweb.design/
* Description: Brief description of plugin functionality
* Version: 1.0.0
* Author: London Web Design
* Author URI: https://londonweb.design/
* License: GPL2
* Text Domain: custom-plugin
*/
// Prevent direct access
if (!defined('ABSPATH')) {
exit;
}
// Plugin code here
Complex Plugin Structure:
custom-plugin/
├── custom-plugin.php (Main plugin file)
├── readme.txt (Plugin documentation)
├── uninstall.php (Cleanup on deletion)
├── includes/
│ ├── class-plugin.php
│ ├── admin/
│ │ ├── class-admin.php
│ │ └── admin-page.php
│ └── public/
│ └── class-public.php
├── assets/
│ ├── css/
│ ├── js/
│ └── images/
└── languages/
Organised structure improves maintainability. Separate concerns through logical file organisation.
Header comments provide WordPress plugin information. Required fields include Plugin Name; remaining fields enhance plugin listings.
Hooks enable plugins modifying WordPress without editing core. Actions execute functions at specific points; filters modify data before output.
Common Action Hooks:
// Plugin initialization
add_action('init', 'customplugin_init');
// Admin initialization
add_action('admin_init', 'customplugin_admin_init');
// Enqueue scripts
add_action('wp_enqueue_scripts', 'customplugin_scripts');
// Save post
add_action('save_post', 'customplugin_save_post');
// WordPress loaded
add_action('wp_loaded', 'customplugin_loaded');
Common Filter Hooks:
// Modify content
add_filter('the_content', 'customplugin_content');
// Modify title
add_filter('the_title', 'customplugin_title');
// Modify excerpt
add_filter('the_excerpt', 'customplugin_excerpt');
// Modify query
add_filter('pre_get_posts', 'customplugin_query');
Custom Hooks:
Create custom hooks enabling others extending your plugin:
// Custom action
do_action('customplugin_before_save', $data);
// Custom filter
$value = apply_filters('customplugin_data', $value);
Hook priority controls execution order. Default priority is 10; lower numbers execute first.
Master hooks creating flexible plugins. Proper hook usage enables powerful functionality without fragile code.
Deep dive into WordPress hooks and filters for comprehensive understanding.
Plugin security prevents vulnerabilities exposing sites to attacks. Security-focused development protects users and enhances professional reputation.
Security Essentials:
Sanitise Input:
// Text fields
$value = sanitize_text_field($_POST['field']);
// Email addresses
$email = sanitize_email($_POST['email']);
// URLs
$url = esc_url_raw($_POST['url']);
// HTML content
$content = wp_kses_post($_POST['content']);
Escape Output:
// HTML context
echo esc_html($string);
// Attribute context
echo '<a href="' . esc_url($url) . '">';
// JavaScript context
echo '<script>var data = ' . wp_json_encode($data) . ';</script>';
Nonces for Forms:
// Generate nonce
wp_nonce_field('custom_action', 'custom_nonce');
// Verify nonce
if (!isset($_POST['custom_nonce']) ||
!wp_verify_nonce($_POST['custom_nonce'], 'custom_action')) {
wp_die('Security check failed');
}
Prepare Database Queries:
global $wpdb;
$results = $wpdb->get_results($wpdb->prepare(
"SELECT * FROM {$wpdb->prefix}table WHERE id = %d",
$id
));
Check Capabilities:
if (!current_user_can('manage_options')) {
wp_die('Insufficient permissions');
}
Security isn't optional. Every plugin processing user input requires security measures.
Combine plugin security with comprehensive WordPress security strategies protecting complete installations.
Admin settings enable users configuring plugins through WordPress dashboard. Professional settings integrate naturally with WordPress admin design.
Register Settings Page:
function customplugin_admin_menu() {
add_options_page(
'Plugin Settings', // Page title
'Custom Plugin', // Menu title
'manage_options', // Capability
'custom-plugin', // Menu slug
'customplugin_settings_page' // Callback
);
}
add_action('admin_menu', 'customplugin_admin_menu');
Settings Page Content:
function customplugin_settings_page() {
?>
<div class="wrap">
<h1><?php echo esc_html(get_admin_page_title()); ?></h1>
<form method="post" action="options.php">
<?php
settings_fields('customplugin_options');
do_settings_sections('custom-plugin');
submit_button();
?>
</form>
</div>
<?php
}
Register Settings:
function customplugin_settings_init() {
register_setting('customplugin_options', 'customplugin_setting');
add_settings_section(
'customplugin_section',
'Plugin Settings',
'customplugin_section_callback',
'custom-plugin'
);
add_settings_field(
'customplugin_field',
'Setting Label',
'customplugin_field_callback',
'custom-plugin',
'customplugin_section'
);
}
add_action('admin_init', 'customplugin_settings_init');
function customplugin_field_callback() {
$value = get_option('customplugin_setting');
?>
<input type="text"
name="customplugin_setting"
value="<?php echo esc_attr($value); ?>">
<?php
}
Settings API provides security, validation, and UI consistency. Use Settings API rather than custom form processing.
Custom tables store plugin data beyond standard WordPress tables. Direct database access requires security vigilance.
Create Custom Table:
function customplugin_create_table() {
global $wpdb;
$table_name = $wpdb->prefix . 'custom_table';
$charset_collate = $wpdb->get_charset_collate();
$sql = "CREATE TABLE $table_name (
id mediumint(9) NOT NULL AUTO_INCREMENT,
user_id mediumint(9) NOT NULL,
data text NOT NULL,
created_at datetime DEFAULT CURRENT_TIMESTAMP,
PRIMARY KEY (id),
KEY user_id (user_id)
) $charset_collate;";
require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
dbDelta($sql);
}
register_activation_hook(__FILE__, 'customplugin_create_table');
Insert Data:
global $wpdb;
$table_name = $wpdb->prefix . 'custom_table';
$wpdb->insert(
$table_name,
array(
'user_id' => get_current_user_id(),
'data' => wp_json_encode($data)
),
array('%d', '%s')
);
Query Data:
global $wpdb;
$table_name = $wpdb->prefix . 'custom_table';
$results = $wpdb->get_results($wpdb->prepare(
"SELECT * FROM $table_name WHERE user_id = %d",
$user_id
));
Update Data:
$wpdb->update(
$table_name,
array('data' => wp_json_encode($new_data)),
array('id' => $id),
array('%s'),
array('%d')
);
Always use prepared statements. Never concatenate user input into queries preventing SQL injection.
Consider whether custom tables necessary. Post meta, user meta, and options often suffice without custom tables.
Proper asset loading prevents conflicts and maintains compatibility. WordPress provides enqueueing functions loading scripts and styles correctly.
Enqueue Styles:
function customplugin_enqueue_styles() {
wp_enqueue_style(
'custom-plugin-style',
plugin_dir_url(__FILE__) . 'assets/css/style.css',
array(),
'1.0.0',
'all'
);
}
add_action('wp_enqueue_scripts', 'customplugin_enqueue_styles');
Enqueue Scripts:
function customplugin_enqueue_scripts() {
wp_enqueue_script(
'custom-plugin-script',
plugin_dir_url(__FILE__) . 'assets/js/script.js',
array('jquery'),
'1.0.0',
true
);
// Localize script (pass PHP data to JavaScript)
wp_localize_script(
'custom-plugin-script',
'customPluginData',
array(
'ajax_url' => admin_url('admin-ajax.php'),
'nonce' => wp_create_nonce('custom_nonce')
)
);
}
add_action('wp_enqueue_scripts', 'customplugin_enqueue_scripts');
Conditional Loading:
function customplugin_conditional_scripts() {
// Only on specific page
if (is_page('contact')) {
wp_enqueue_script('contact-form-script');
}
// Only in admin
if (is_admin()) {
wp_enqueue_style('admin-style');
}
}
add_action('wp_enqueue_scripts', 'customplugin_conditional_scripts');
Never link scripts directly in HTML. Enqueueing ensures proper loading order and dependency management.
Conditional loading improves performance. Load assets only where needed.
AJAX enables dynamic functionality without page reloads. WordPress provides built-in AJAX handling through admin-ajax.php.
JavaScript AJAX Request:
jQuery(document).ready(function($) {
$('#submit-button').on('click', function(e) {
e.preventDefault();
$.ajax({
url: customPluginData.ajax_url,
type: 'POST',
data: {
action: 'custom_ajax_action',
nonce: customPluginData.nonce,
data: $('#input-field').val()
},
success: function(response) {
if (response.success) {
console.log(response.data);
}
}
});
});
});
PHP AJAX Handler:
function customplugin_ajax_handler() {
// Verify nonce
check_ajax_referer('custom_nonce', 'nonce');
// Check permissions if needed
if (!current_user_can('read')) {
wp_send_json_error('Insufficient permissions');
}
// Process request
$data = sanitize_text_field($_POST['data']);
// Perform action
$result = custom_process_data($data);
// Send response
if ($result) {
wp_send_json_success($result);
} else {
wp_send_json_error('Processing failed');
}
}
add_action('wp_ajax_custom_ajax_action', 'customplugin_ajax_handler');
add_action('wp_ajax_nopriv_custom_ajax_action', 'customplugin_ajax_handler');
wp_ajax_{action} handles logged-in users. wp_ajax_nopriv_{action} handles logged-out users.
Always verify nonces in AJAX handlers. Security applies equally to AJAX requests.
Activation and deactivation hooks run when plugins activate or deactivate. Use for setup and cleanup tasks.
Activation Hook:
function customplugin_activate() {
// Create custom tables
customplugin_create_table();
// Set default options
add_option('customplugin_version', '1.0.0');
add_option('customplugin_settings', array());
// Flush rewrite rules if registering post types
flush_rewrite_rules();
}
register_activation_hook(__FILE__, 'customplugin_activate');
Deactivation Hook:
function customplugin_deactivate() {
// Cleanup temporary data
delete_transient('customplugin_cache');
// Flush rewrite rules
flush_rewrite_rules();
}
register_deactivation_hook(__FILE__, 'customplugin_deactivate');
Uninstall Hook:
// uninstall.php
if (!defined('WP_UNINSTALL_PLUGIN')) {
exit;
}
// Delete options
delete_option('customplugin_settings');
// Drop custom tables
global $wpdb;
$table_name = $wpdb->prefix . 'custom_table';
$wpdb->query("DROP TABLE IF EXISTS $table_name");
Activation handles setup. Deactivation handles temporary cleanup. Uninstall removes all plugin data.
Never delete data on deactivation. Users may reactivate plugins expecting data persistence.
Thorough testing prevents bugs reaching users. Systematic testing validates functionality across scenarios.
Testing Checklist:
Functionality Testing:
Compatibility Testing:
Security Testing:
Performance Testing:
Debugging Tools:
// Enable debugging
define('WP_DEBUG', true);
define('WP_DEBUG_LOG', true);
define('WP_DEBUG_DISPLAY', false);
// Debug logging
error_log('Debug message: ' . print_r($data, true));
// Query Monitor plugin for performance
// Debug Bar plugin for debugging
Professional testing distinguishes quality plugins from problematic ones. Testing investment prevents support nightmares.
How long does learning WordPress plugin development take?
Basic WordPress plugin development requires 4-8 weeks learning PHP, WordPress functions, and plugin patterns. Building simple functional plugins takes additional 2-4 weeks practice. Professional-quality plugin development proficiency requires 6-12 months consistent practice. Advanced plugin development mastery takes years. However, creating useful plugins becomes achievable within months for developers with PHP experience. Start simple, progressively building complexity as skills develop.
Can I build plugins without PHP experience?
No, WordPress plugin development fundamentally requires PHP knowledge. Plugins execute server-side code requiring PHP proficiency. Learn PHP basics before attempting plugin development. However, simple plugins provide excellent PHP learning projects. Start with tutorials combining PHP and WordPress learning simultaneously. Expect steeper learning curves but achievable for motivated learners. Consider learning fundamental PHP through dedicated courses before WordPress-specific development.
Should I build custom plugin or use existing ones?
Use existing plugins when available, well-maintained, and meeting requirements. Custom plugin development costs thousands in development time. Build custom plugins only when: no suitable alternatives exist, specific business logic requires custom code, or existing plugins prove inadequate. Evaluate total cost including development, testing, maintenance, and support. Most needs satisfy through existing plugins; custom development suits unique requirements justifying investment.
How do I make plugins update-compatible?
Follow WordPress coding standards ensuring compatibility with WordPress updates. Avoid deprecated functions; use current WordPress APIs. Never modify WordPress core. Test plugins with WordPress beta versions before major releases. Use proper hooks rather than direct modifications. Follow semantic versioning for plugin versions. Well-coded plugins remain compatible across WordPress versions. Monitor WordPress development blog for upcoming changes affecting plugins.
Can I sell WordPress plugins I develop?
Yes, WordPress plugins can be sold through CodeCanyon, your website, or subscription models. Plugins submitted to WordPress.org must be free and GPL-licensed. Commercial plugins require ongoing support, regular updates, comprehensive documentation, and security vigilance. GPL licensing allows buyers modifying and redistributing code. Premium plugins justify prices through support, updates, and professional quality. Consider support commitments and maintenance requirements before commercialising plugins.
What's the difference between plugins and mu-plugins?
Regular plugins install through WordPress admin, users activate individually, and can be deactivated. Must-use plugins (mu-plugins) reside in wp-content/mu-plugins/, load automatically without activation, and cannot be deactivated through admin. Mu-plugins suit site-critical functionality requiring automatic loading. Use regular plugins for optional functionality; mu-plugins for essential site functionality. Mu-plugins lack UI for activation/deactivation or settings in admin.
Do WordPress plugins need ongoing maintenance?
Yes, plugins require maintenance ensuring WordPress compatibility, security, and functionality. Monitor WordPress updates testing plugin compatibility. Update dependencies and libraries. Fix bugs reported by users. Add features as requirements evolve. Respond to security vulnerabilities promptly. Budget development time for ongoing maintenance. Abandoned plugins create security risks and compatibility issues. Proper maintenance protects plugin reputation and user security.
Related WordPress Development Topics:
Written by the WordPress Development Team at London Web Design, building custom plugins for London businesses since 2010.
