Extending WordPress: widgets, plugins or functions.php ?

As a developer using wordpress for all sorts of needs, you’ll be often faced with this question: should a particular functionality be implemented as an external plugin, as a function inside your theme’s functions.php or as a widget?

In my experience, the proper answer depends on the following aspects:

1. should the functionality be available sitewide or only on specific parts of the website OR will it be a permanent feature of the website during its lifetime? If the answer is “yes”, you should definitely consider adding the functionality to functions.php
2. should it be actionable by the website content manager, meaning: by the people who act on the WordPress installation as “Editor”? In such case, you should make it available via the WP-admin interface to the Editor, as a Widget
3. should it be actionable by the website system administrator, meaning: by the people who act on the WordPress installation as “Administrator”? In this latter case, you should make it available on the WP-admin to the Administrator, either as a Widget or as a Plugin that can be desactivated.
4. Layoutwise, should the functionality frontend display move around the frontend interface? That’s definitely something Widgets are designed for, so go for Widgets.

This short post was meant to clarify a frequent and important question in WordPress development. Note that WordPress is as flexible as a Eastern Europe athlete, so it’s more of a general rule but everything is pretty much possible. For instance, some plugins provide Widgets to give more control to the WP-admin users, WP roles can be tweaked so that Editors, or even Authors can have access to the plugin control interface, etc.