WordPress Function Reference




The files of WordPress define many useful PHP functions. 
Some of the functions, known as Template Tags, are defined especially for use in WordPress Themes. 
There are also some functions related to actions and filters (the Plugin API), which are therefore used primarily for developing Plugins. 
The rest are used to create the core WordPress functionality.

Many of the core WordPress functions are useful to Plugin and Theme developers. 
So, this article lists most of the core functions, excluding Template Tags. 
At the bottom of the page, there is a section listing other resources for finding information about WordPress functions. 
In addition to this information, the WordPress Code Reference site details all the WordPress functions by version since 2.6.1.

Functions by category

Post, Custom Post Type, Page, Attachment and Bookmarks Functions

Posts

Custom Post Status

Custom Post Type

Post insertion/removal

Pages

Custom Fields (postmeta)

Attachments

Bookmarks

Terms


Others

Category, Tag and Taxonomy Functions

Categories

Category Creation

Tags

Taxonomy

User and Author Functions

Admins, Roles and Capabilities

Users and Authors

User meta

User insertion/removal

Login / Logout

Feed Functions

HTTP API Functions


Comment, Ping, and Trackback Functions

Comments Loop

Comments Pagination


Action, Filter, and Plugin Functions

Filters (Reference)

Actions (Reference)

Plugins (Reference)

Widgets (Reference)


Settings (Reference)

Shortcodes (Reference)

Theme-Related Functions

Include functions

Other functions

Formatting Functions

Miscellaneous Functions

Time/Date Functions

Serialization

Options

Transients

Admin Menu Functions

Toolbar Functions

Form Helpers


Nonces and Referers (Security)

XMLRPC

Localization

Cron (Scheduling)

Conditional Tags Index

Script and Style Registration

sql

Miscellaneous

Multisite functions

As of v3.0, WordPress includes WPMU functionality. Old WPMU functions reference can be found at http://codex.wordpress.org/WPMU_Functions (deprecated page).

Multisite administration Functions

These functions are found in file wp-admin/includes/ms.php (since 3.0.0).


Multisite Functions

Site/blog functions that work with the blogs table and related data, found in file wp-includes/ms-blogs.php (since 3.0.0).

Defines constants and global variables that can be overridden, generally in wp-config.php, found in file wp-includes/ms-default-constants.php (since 3.0.0).

Multisite WordPress API, found in file wp-includes/ms-functions.php (since 3.0.0).

These functions are needed to load Multisite, found in file wp-includes/ms-load.php (since 3.0.0).