This manual is no longer being maintained for TYPO3 versions 11.5 and above. The majority of the content has been migrated to the Extbase or Fluid sections in "TYPO3 Explained".

Coding Guidelines

Extbase and Fluid follow the principle of Convention over Configuration. That means that many tasks will work automatically if you respect certain naming conventions for classes, files and method names. Furthermore, this principle improves the consistency and readability of your code. Thus it is much easier for extension developers to understand how unknown extensions (based on Extbase) work, because the structure is always the same und common tasks are solved in the same way.

With Extbase and Fluid we set quite an emphasis on the intuitive and logical naming scheme of classes, methods and variables. Our goal is to provide the source code as readable as possible, because the names are already reflecting what the source code does.

Generally, classes are written in UpperCamelCase and methods and variables are written in lowerCamelCase. In addition, the name must be detailed and meaningful. Abbreviations are to be avoided.

Folder structure

Every extension based on Extbase contains certain folders in the main directory:


Here resides the complete source code for the extension. Only PHP files are allowed, each one containing exactly one class or interface. All classes (or interfaces) are loaded via the autoloader mechanism when needed.


The configuration of the extension is located here: FlexForm configuration, TCA definitions, TSconfig and TypoScript files. Subfolder can be created when they are needed or helpful.


Contains the documentation of the extension.


This folder contains static resources of the extension. This means all files which are not PHP files but are necessary for the execution of the extension. This might be code from libraries, template files, images, css files and so on.

It is distinguished between public (Public/) and private (Private/) resources. In the folder Private/ there should be a .htaccess file, which is blocking direct access to non public files.


Contains non public resources of the extension.


Contains public resources of the extension.

Within these two folder the authors of the extension can choose the structure freely, but we recommend the following structure:


This is a good place for images, CSS files or media files, which are delivered directly to the client.


Here are the default Fluid templates for the extension.


Contains PHP code, which is not compatible to the naming conventions like external PHP libraries, procedural code and so on. If you run TYPO3 in composer mode, you should define the autoloading for said folder in the composer.json of your extension.

If you don't run TYPO3 in composer mode, the autoloader of TYPO3 will automatically search for php files in all extensions.


All unit tests are found here. The structure should be the same as in Classes. All test classes should end with Test.


Contains the configuration for the extension manager of TYPO3 like metadata as the name, the description and the author of the extension.


The icon of the extension, which will be visible in the Extension Manager. It should have a size of 18 x 16 px.


This file contains configuration of the Frontend Plugins.


This file contains configuration for the backend.


This is a file with SQL commands for the definition of the database tables.

File and class names

Class names in Extbase are composed with the following parts:

  1. the vendor prefix. For example, if your name is Example, then this part could be Ex.

  2. the name of the extension in UpperCamelCase. For example, if the extension-key is blog_example, then this part of the classname is BlogExample.

  3. the path within the Classes/ folder down to the folder, where the file containing the class resides.

In table A-1 you see some naming examples for file and class names.

Table A-1: Examples for class names


extension key











Interfaces end with Interface, for example TYPO3\CMS\Extbase\Mvc\RequestInterface. With abstract classes the last part of the name always begins with Abstract, for example \TYPO3\CMS\Extbase\Property\TypeConverter\AbstractTypeConverter.