---
title: "TYPO3 Explained"
manual: "TYPO3 Explained"
version: "14.3"
permalink: "https://docs.typo3.org/permalink/t3coreapi:api-overview@14.3"
source: "Index.rst"
start: true
rendered: "2026-09-20T16:07:38+00:00"
---

# TYPO3 Explained {#api-overview}

**[API A-Z](https://docs.typo3.org/permalink/t3coreapi:api@14.3)**

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

**[Administrations](https://docs.typo3.org/permalink/t3coreapi:administration@14.3)**

Including [Installations](https://docs.typo3.org/permalink/t3coreapi:installation@14.3), [Upgrades and updates](https://docs.typo3.org/permalink/t3coreapi:upgrading@14.3),
[Troubleshooting for administrators](https://docs.typo3.org/permalink/t3coreapi:troubleshooting-index@14.3), and
[Backend User Management](https://docs.typo3.org/permalink/t3coreapi:user-management@14.3)

**[Configuration](https://docs.typo3.org/permalink/t3coreapi:configuration@14.3)**

Including [System configuration and the global settings.php](https://docs.typo3.org/permalink/t3coreapi:typo3confvars@14.3), [TypoScript](https://docs.typo3.org/permalink/t3coreapi:typoscript@14.3), the [Configuration inspector (readonly)](https://docs.typo3.org/permalink/t3coreapi:config-module@14.3),
and [Feature toggle API](https://docs.typo3.org/permalink/t3coreapi:feature-toggles@14.3)

**[Coding guidelines](https://docs.typo3.org/permalink/t3coreapi:cgl@14.3)**

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@14.3)**

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@14.3)**

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

**[Security guidelines](https://docs.typo3.org/permalink/t3coreapi:security@14.3)**

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@14.3)**

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