# Extensions

Extensions are extra packages that add functionality to a Flask application. For example, an extension might add support for sending email or connecting to a database. Some extensions add entire new frameworks to help build certain types of applications, like a REST API.

## Finding Extensions

Flask extensions are usually named “Flask-Foo” or “Foo-Flask”. You can search PyPI for packages tagged with Framework :: Flask.

## Using Extensions

Consult each extension’s documentation for installation, configuration, and usage instructions. Generally, extensions pull their own configuration from `app.config` and are passed an application instance during initialization. For example, an extension called “Flask-Foo” might be used like this:

    from flask_foo import Foo

    foo = Foo()

    app = Flask(__name__)
    app.config.update(
        FOO_BAR='baz',
        FOO_SPAM='eggs',
    )

    foo.init_app(app)

## Building Extensions

While the PyPI contains many Flask extensions, you may not find an extension that fits your need. If this is the case, you can create your own. Read Flask Extension Development to develop your own Flask extension.