Installed_Apps Explained

1. Introduction

INSTALLED_APPS is a list in your settings file that tells Django which apps are active in your project. Django uses it to discover models, run migrations, load template directories, register admin classes, and more.

Getting this list right matters. Missing an app means its models are invisible to Django. Adding an app incorrectly causes errors at startup. This guide covers what goes in the list, how Django uses it, and the mistakes to avoid.

• You should already have myproject set up with the pages app created.
• Your .venv must be active and Django 5.2 installed.

2. The default apps

When you create a new Django project, INSTALLED_APPS already contains six built-in apps:

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
]

Here is what each one does:

• django.contrib.admin — the Django admin panel. Gives you a ready-to-use interface to manage your database records.
• django.contrib.auth — the authentication system. Provides users, groups, permissions, and password hashing.
• django.contrib.contenttypes — a framework for working with generic relations between models. Required by auth and admin.
• django.contrib.sessions — manages user sessions. Required if you use login/logout or store data between requests.
• django.contrib.messages — a one-time notification system. Used to show success or error messages after form submissions.
• django.contrib.staticfiles — manages static files like CSS and JavaScript. Required for the template tag to work.

3. Adding your own apps

Every app you create with python manage.py startapp must be added to INSTALLED_APPS before Django recognizes it. Add your apps below the built-in ones:

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    # your apps
    'pages',
]

You can use either the short form 'pages' or the full AppConfig path 'pages.apps.PagesConfig'. Both work. Use the full path when your app has a custom AppConfig with extra configuration. We covered this in the AppConfig and the App Registry tutorial.

4. Adding third party apps

When you install a third party package with pip — for example django-crispy-forms or djangorestframework — you also need to add it to INSTALLED_APPS. The package documentation always tells you the exact string to use.

A common convention is to group your apps into three sections with comments:

INSTALLED_APPS = [
    # Django built-in apps
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    # Third party apps
    'rest_framework',
    'crispy_forms',
    # Your apps
    'pages',
]

5. How Django uses INSTALLED_APPS

Django reads INSTALLED_APPS at startup and uses it for several things:

• Model discovery — Django finds all models.py files from apps in this list. If your app is not listed, its models do not exist as far as Django is concerned.
• Migrations — makemigrations only generates migrations for apps in INSTALLED_APPS. Missing an app here means its database tables are never created.
• Template discovery — when APP_DIRS: True is set in TEMPLATES, Django looks for a templates/ folder inside each app listed here.
• Static files — Django collects static files from a static/ folder inside each listed app when you run collectstatic.
• Admin auto-discovery — Django automatically imports admin.py from each listed app so registered models appear in the admin panel.

6. Common mistakes

Forgetting to add the app after startapp

Running python manage.py startapp pages creates the folder but does not register the app. You must add it to INSTALLED_APPS yourself. The symptom is that makemigrations finds no changes even though you added models.

Wrong app name or path

If the string in INSTALLED_APPS does not match the actual app folder name or the dotted path to the AppConfig class, Django raises an ImproperlyConfigured error at startup.

# Wrong — folder is named 'pages' not 'page'
'page',

# Correct
'pages',

Removing an app without removing its migrations

If you remove an app from INSTALLED_APPS but leave its migration files on disk, Django may raise errors when running migrate. Always clean up migration files when permanently removing an app.

Duplicate entries

Adding the same app twice — once as 'pages' and once as 'pages.apps.PagesConfig' — causes Django to raise an error about duplicate app labels. Use one form consistently.

7. Removing default apps

You can remove built-in apps you do not need, but be careful — some apps depend on others:

• Removing django.contrib.admin is fine if you do not use the admin panel.
• Removing django.contrib.auth means no users, groups, or permissions — also removes the admin.
• Removing django.contrib.contenttypes breaks auth and admin.
• Removing django.contrib.staticfiles means stops working.

8. Next steps

You now have a solid understanding of INSTALLED_APPS and how Django uses it. The next step is to look at project structure best practices — how to organize your apps, templates, static files, and settings as your project grows.