---
title: "TYPO3 Explained"
manual: "TYPO3 Explained"
version: "main"
permalink: "https://docs.typo3.org/permalink/t3coreapi:api-overview@main"
source: "Index.rst"
start: true
modified: "2026-09-16T09:14:56+00:00"
---

# TYPO3 Explained

**[API A-Z](https://docs.typo3.org/permalink/t3coreapi:api@main)**

This chapter describes the core functionality of TYPO3 including API and framework configuration.

**[Administrations](https://docs.typo3.org/permalink/t3coreapi:administration@main)**

Including [Installations](https://docs.typo3.org/permalink/t3coreapi:installation@main), [Upgrades and updates](https://docs.typo3.org/permalink/t3coreapi:upgrading@main),
[Troubleshooting for administrators](https://docs.typo3.org/permalink/t3coreapi:troubleshooting-index@main), and
[Backend User Management](https://docs.typo3.org/permalink/t3coreapi:user-management@main)

**[Configuration](https://docs.typo3.org/permalink/t3coreapi:configuration@main)**

Including [System configuration and the global settings.php](https://docs.typo3.org/permalink/t3coreapi:typo3confvars@main), [TypoScript](https://docs.typo3.org/permalink/t3coreapi:typoscript@main), the [Configuration inspector (readonly)](https://docs.typo3.org/permalink/t3coreapi:config-module@main),
and [Feature toggle API](https://docs.typo3.org/permalink/t3coreapi:feature-toggles@main)

**[Coding guidelines](https://docs.typo3.org/permalink/t3coreapi:cgl@main)**

This chapter contains a description of the formal requirements or standards
regarding coding that you should adhere to when you develop TYPO3
extensions or Core parts.

**[Extension development](https://docs.typo3.org/permalink/t3coreapi:extension-development@main)**

Learn how to write site packages and other custom extension with or
without Extbase.

**[PHP architecture](https://docs.typo3.org/permalink/t3coreapi:cgl-php-architecture@main)**

General PHP architectural strategies in TYPO3 core development and best
practices for extension developers.

**[Security guidelines](https://docs.typo3.org/permalink/t3coreapi:security@main)**

This chapter describes some typical risks and advises how to protect a
TYPO3 site in order to ensure it is and stays secure and stable.

**[Automated testing](https://docs.typo3.org/permalink/t3coreapi:testing@main)**

This chapter goes into details about automatic testing: Writing,
maintaining and running them in various scopes.