Most plugins on your site can be switched on and off with a single click. A must-use plugin is different. It is a plugin that WordPress loads automatically on every page, and you can't deactivate it from the dashboard.
Hosting companies and developers use them for code that must always run. Let's see how they work and when you should use one.
Where Do Must-Use Plugins Live?
Must-use plugins, often called MU plugins, sit in a special folder named wp-content/mu-plugins. WordPress loads every PHP file placed directly in this folder, before it loads the normal plugins. There is no activate button, because they are always active.
Think of regular plugins as light switches that you flip on and off. MU plugins are more like the main wiring of the house, which simply stays on.
How to Add a Must-Use Plugin
- First, connect to your site using FTP or your host's file manager.
- Now, open the
wp-contentfolder and create a folder namedmu-pluginsif it does not exist yet. - Next, upload your PHP file into this new folder.
- Here, go to Plugins in your dashboard and click the Must-Use link to confirm it is listed.
If you are new to FTP, our guide on accessing WordPress websites with FTP makes the first step pretty easy.
WordPress only reads PHP files sitting directly inside mu-plugins, not files inside subfolders. If a plugin comes in its own folder, you need a small loader file in the main folder that includes it.
When Should You Use MU Plugins?
MU plugins are perfect for small snippets that nobody should turn off by mistake. For example, you might use one for code that registers a custom post type your content depends on. Many managed hosts also use this folder for their own caching and security tools.
However, there is one catch. WordPress does not show update notices for MU plugins, so you have to update them by hand. If you only want to keep custom code separate from your theme, a site-specific plugin is often the easier choice.
That's it. Must-use plugins are simple, always on and best kept for code your site truly can't live without. Drop your questions in the comment section below.