WordPress believes in keeping it a simple/easy to use CMS or Content Management System, and a lot of thought goes into including new functionality as a part of the "core" WordPress code, in order to keep WordPress fast and lightweight. Still, users often find the need to graft additional functionality onto WordPress to meet their needs. This section of the Codex offers guidelines and references for anyone wishing to modify, extend, or contribute to WordPress.
You may also wish to consult the Developer Documentation FAQ
- Writing a Plugin - The best starting place for learning about how to develop plugins
- WordPress Coding Standards - General information about coding standards for WordPress development
- Debugging in WordPress - Reference and guide for using the built-in debugging system in WordPress.
- Data Validation - A must-read for WordPress plugin authors. Describes the functions used by WordPress to validate and sanitize data. Plugin authors should be familiar with these functions and ideas.
- Plugin Submission and Promotion - Once you have written your plugin, here are some hints on distributing it widely
- Migrating Plugins and Themes - Contains information on how to upgrade your Plugin so it will work from version to version of WordPress
- Function Reference - Complete PHP function reference for WordPress (version 2.1, with links to previous versions)
- Global Variables - A list of all global variables created by WordPress
- Plugin Resources - Comprehensive list of other references for plugin development
- Custom Post Types - Creating new types of posts other than the posts that display on the main loop.
- Plugin API - Hooks, Actions, and Filters to use in your Plugins (version 2.1; has links to older version articles)
- Shortcode API - A tutorial and reference for the shortcode API (new in version 2.5)
- Dashboard Widgets API - A reference with examples for adding new widgets to the admin dashboard.
- Settings API - A reference with examples for adding new settings to existing settings screens.
- Options API - Details about the generic option storage system.
- Transients API - Details about the temporary/time-constrained data storage system.
- Widgets API - A reference with examples for creating widgets for use in sidebars.
- Quicktags API - A reference for adding buttons to the HTML editor.
- Rewrite API - Details about the URL rewriting API.
Contributing to WordPress
- Contributing to WordPress - Main starting point if you would like to contribute to core WordPress development, documentation, support, translations, or financial health
- Automated Testing - Testing WordPress using the automated test suite and how to use the tools and write test cases.
- Data Validation - A must-read for WordPress contributors. Describes the functions used by WordPress to validate and sanitize data. Developers contributing to WordPress' codebase should be familiar with these functions and ideas.
- Release Philosophy - The philosophy of WordPress releases.
Forums, Lists, and Blogs
- Mailing Lists - WordPress mailing lists are for programmers, documentation, and development
- IRC - WordPress IRC channels
- http://wordpress.org/support - WordPress Support Forums
- http://wordpress.org/development - WordPress Development Blog
- http://planet.wordpress.org - Aggregate of many blogs discussing WordPress (official)
- http://planetwordpress.planetozh.com/ - Another aggregate of many blogs discussing WordPress mostly plugins and themes (unofficial)
Other Information of Interest
- Advanced Topics - Annotated list of many articles on advanced WordPress topics
- Query Overview - Description of the WordPress query process used to find posts and display them
- Reporting Bugs - Information on reporting and fixing WordPress bugs
- Using Subversion - Introduction to SVN, the source code repository used by WordPress
- Development Team - The members of the development team.
- WP Hook Database - Thorough and extremely useful reference of all hooks (actions and filters) used in WordPress cross referenced by version.
WordPress Source Code
- PHPXref sites: PHPXref creates a cross reference of WordPress files, functions and variables.
- WordPress Function History Table - List of what version each WordPress function was added in; PlanetOzh recommends: "see related WordPress Functions Implementation History Tool for more information (and for a more usable tool)"
- WordPress Variable Report - A list of WordPress functions, listing what version of PHP every function requires (and if there's a compatible function available), what variables/arguments in functions are unused, and what functions/variables each class contains (and their default values).
- WordPress Development Search (Google CSE)
- WordPress Function/Hook Lookup