# Looker extension framework documentation

This section provides an introduction to the Looker extension framework, which lets you build a custom application within Looker. Select a subtopic to dive in:

- [Looker extension framework](https://docs.cloud.google.com/looker/docs/intro-to-extension-framework) --- A description of the extension framework, including lists of features and requirements.
- [Building an extension](https://docs.cloud.google.com/looker/docs/extension-intro-to-building) --- A procedure to create a simple "Hello World" extension to which you can then add your own custom functions.
- [Extension React and JavaScript code examples](https://docs.cloud.google.com/looker/docs/extension-framework-react-and-js-code-examples) --- A list of example functions written in React and JavaScript that you can add to an extension.