---
title: "TYPO3 Explained"
manual: "TYPO3 Explained"
version: "12.4"
permalink: "https://docs.typo3.org/permalink/t3coreapi:api-overview@12.4"
source: "Index.rst"
start: true
rendered: "2026-10-21T15:29:37+00:00"
---

> [!WARNING]
> **Attention**
>
> TYPO3 v12 has reached end-of-life as of April 30th 2026 and
> is no longer being maintained. Use the version switcher on the top
> left of this page to select documentation for a supported version of TYPO3.
>
> Need more time before upgrading?
> You can purchase Extended Long Term Support (ELTS) for TYPO3 v12 here:
> [TYPO3 ELTS](https://typo3.com/services/extended-support-elts).

<a id="start"></a>

# TYPO3 Explained {#api-overview}

**[API A-Z](https://docs.typo3.org/permalink/t3coreapi:api@12.4)**

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

**[Administrations](https://docs.typo3.org/permalink/t3coreapi:administration@12.4)**

Including [Installations](https://docs.typo3.org/permalink/t3coreapi:installation@12.4), [Upgrades and updates](https://docs.typo3.org/permalink/t3coreapi:upgrading@12.4),
[Troubleshooting for administrators](https://docs.typo3.org/permalink/t3coreapi:troubleshooting-index@12.4), and
[Backend User Management](https://docs.typo3.org/permalink/t3coreapi:user-management@12.4)

**[Configuration](https://docs.typo3.org/permalink/t3coreapi:configuration@12.4)**

Including [System configuration and the global settings.php](https://docs.typo3.org/permalink/t3coreapi:typo3confvars@12.4), [TypoScript](https://docs.typo3.org/permalink/t3coreapi:typoscript@12.4), the [Configuration module](https://docs.typo3.org/permalink/t3coreapi:config-module@12.4),
and [Feature toggle API](https://docs.typo3.org/permalink/t3coreapi:feature-toggles@12.4)

**[Coding guidelines](https://docs.typo3.org/permalink/t3coreapi:cgl@12.4)**

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@12.4)**

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

**[Security guidelines](https://docs.typo3.org/permalink/t3coreapi:security@12.4)**

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@12.4)**

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