Application Structure

To get the most out of CodeIgniter, you need to understand how the application is structured, by default, and what you can change to meet the needs of your application.

Default Directories

A fresh install has five directories:

  • app

  • public

  • writable

  • tests

  • vendor or system

Each of these directories has a very specific part to play.


The app directory is where all of your application code lives. This comes with a default directory structure that works well for many applications.

The following folders make up the basic contents:

    Config/         Stores the configuration files
    Controllers/    Controllers determine the program flow
    Database/       Stores the database migrations and seeds files
    Filters/        Stores filter classes that can run before and after controller
    Helpers/        Helpers store collections of standalone functions
    Language/       Multiple language support reads the language strings from here
    Libraries/      Useful classes that don't fit in another category
    Models/         Models work with the database to represent the business entities
    ThirdParty/     ThirdParty libraries that can be used in application
    Views/          Views make up the HTML that is displayed to the client

Because the app directory is already namespaced, you should feel free to modify the structure of this directory to suit your application’s needs.

For example, you might decide to start using the Repository pattern and Entities to work with your data. In this case, you could rename the Models directory to Repositories, and add a new Entities directory.

All files in this directory live under the App namespace, though you are free to change that in app/Config/Constants.php.



If you install CodeIgniter with Composer, the system is located in vendor/codeigniter4/framework/system.

This directory stores the files that make up the framework, itself. While you have a lot of flexibility in how you use the application directory, the files in the system directory should never be modified. Instead, you should extend the classes, or create new classes, to provide the desired functionality.

All files in this directory live under the CodeIgniter namespace.


The public folder holds the browser-accessible portion of your web application, preventing direct access to your source code.

It contains the main .htaccess file, index.php, and any application assets that you add, like CSS, javascript, or images.

This folder is meant to be the “web root” of your site, and your web server would be configured to point to it.


This directory holds any directories that might need to be written to in the course of an application’s life. This includes directories for storing cache files, logs, and any uploads a user might send.

You should add any other directories that your application will need to write to here. This allows you to keep your other primary directories non-writable as an added security measure.


This directory is set up to hold your test files. The _support directory holds various mock classes and other utilities that you can use while writing your tests.

This directory does not need to be transferred to your production servers.

Modifying Directory Locations

If you’ve relocated any of the main directories, you can change the configuration settings inside app/Config/Paths.php.

Please read Managing your Applications.