How do you write a custom plugin from scratch?

1. Plan the Plugin

• Decide what the plugin will do (feature/functionality).
• Name it uniquely to avoid conflicts.

2. Create the Plugin Folder & File

1. Go to: bashCopyEdit/wp-content/plugins/
2. Create a folder: perlCopyEditmy-custom-plugin
3. Inside, create a PHP file: perlCopyEditmy-custom-plugin.php

3. Add the Plugin Header

This tells WordPress your file is a plugin:

<?php
/*
Plugin Name: My Custom Plugin
Plugin URI: https://example.com
Description: A simple plugin that does something useful.
Version: 1.0
Author: Your Name
Author URI: https://example.com
License: GPL2
*/

4. Write the Plugin Code

Example: Add a custom message at the end of every post.

function mcp_add_footer_message( $content ) {
    if ( is_single() ) {
        $content .= '<p style="color: blue;">Thank you for reading!</p>';
    }
    return $content;
}
add_filter( 'the_content', 'mcp_add_footer_message' );

5. Activate the Plugin

• Go to WordPress Admin → Plugins.
• Find My Custom Plugin.
• Click Activate.

6. Best Practices

• Prefix all function names to avoid conflicts (mcp_ in example).
• Use hooks (add_action, add_filter) instead of modifying core files.
• Sanitize and validate all user input.
• Escape all output (esc_html(), esc_attr()).
• Add uninstall.php for cleanup when plugin is deleted.

7. Optional: Add More Files

• includes/ folder for organizing large plugins.
• assets/css/ and assets/js/ for styling and scripts.
• readme.txt for WordPress.org submission.

💡 Analogy:
Creating a plugin is like adding a new appliance to your kitchen — it’s separate from the main house (WordPress core), can be plugged in or unplugged anytime, and gives you extra functionality without altering the structure.