Best WordPress functions file plugins, why you should use them and what they do

Here’s a list of the best WordPress functions file plugins currently available. This list includes free and premium functions plugins, as well as plugins designed for the novice to expert and everyone in between. We recommend using a functions plugin when running Woocommerce.

What is a functions file?

A functions file is a theme file that is used to define functions, classes, actions and filters in both the admin area and user-facing frontend. You can use the theme functions file, known as functions.php, to add features and extend the functionality of your WordPress site. It’s a bit like a plugin, without being a plugin.

Why would you use a functions plugin?

When making edits to the functions.php file any changes you make stay with the theme, and if you edit the live theme and not the child theme the changes will be lost when you update the theme. By using a functions plugin the features and extensions that you add stay with your website, regardless of the theme you are using. This can be extremely useful when using Woocommerce, as additions are usually related to the Woocommerce plugin and not the specific theme you are using.

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Another benefit of a functions plugin is that they normally prevent changes being saved and sent live if there is an error in the code. This can help prevent the dreaded white screen of death that can pop up if there is a minor mistake in the function you have added.

Best WordPress functions plugins

My Custom Functions


I’ll begin with My Custom Functions. This is perhaps the most widely used functions plugin in the WordPress repository. It has an easy to use editor, the ability to turn on and off the custom functions and it will normally prevent bad changes from being sent live. If a bad edit does go live the plugin has a folder called START that can be manually disabled by renaming STOP using FTP or file manager in CPanel. FYI, this is the plugin that I use.

Custom Functions Starter Kit by 99 Robots

Unlike My Custom Functions above, this plugin has a list of common custom functions that can be activated with a simple tick box and a save. This plugin has been built for ease of use and designed for the novice WordPress user.

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Functionality is a plugin for creating a custom functions file. Once you have created the file you are free to edit the file and delete the plugin. While this plugin works and serves its purpose well, it doesn’t have the failsafe inclusions that My Custom Functions has. This is designed for the more advanced user who knows hoe to make edits and fix mistakes.

My Custom Functions PRO

My Custom Functions Pro is an improved version of My Custom Functions. While the free version does the job required, the Pro version ratchets it up a level.

The pro version does everything the free one does, but more. WIth the Pro version you can have:

  • Unlimited number of fields
  • Automatic backup of all functions to a file
  • Ability to temporarily disable the certain function
  • Ability to collapse/expand certain fields with code
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