Coding Guidelines

More information is found in the Coding Guidelines section of the "TYPO3 Explained" manual (formerly known as "Core API").

This is just a very brief overview.


Make sure you are using the correct PHP code style. It is based on the TYPO3 Coding Standards, (which follows PER-CS1.0 / PSR-12 and transition into PER-CS2.0 at the time of this writing), and covered in the TYPO3 Coding Guidelines.

See PhpStorm setup: CGL for information on how to configure the correct coding style.

The Appendix contains information on scripts to check / fix coding guideline issues: CGL check and fix


The following rules should be applied for JavaScript: Airbnb JavaScript Style Guide


The following rules should be applied for TypeScript: Excel Micro TypeScript Style Guide.

Xliff files

Language files are usually stored in a Folder Resources/Private/Language in files with the ending .xlf. While no tabs are allowed to indent in PHP files, you should edit Xliff files using tabs.