---
title: "Coding Guidelines"
manual: "TYPO3 Core Contribution Guide"
version: "main"
permalink: "https://docs.typo3.org/permalink/t3contribute:appendix-cgl"
source: "Appendix/Cgl.rst"
rendered: "2026-10-09T09:48:53+00:00"
---

# Coding Guidelines {#appendix-cgl}

More information is found in the [Coding Guidelines](https://docs.typo3.org/m/typo3/reference-coreapi/main/en-us/CodingGuidelines/Index.html#cgl)
section of the "TYPO3 Explained" manual (formerly known as "Core API").

This is just a very brief overview.

## PHP {#appendix-cgl-php}

Make sure you are using the correct PHP code style. It is based on
the [TYPO3 Coding Standards](https://github.com/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](https://docs.typo3.org/m/typo3/reference-coreapi/main/en-us/CodingGuidelines/Index.html#cgl).

See [PhpStorm setup: CGL](https://docs.typo3.org/permalink/t3contribute: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](https://docs.typo3.org/permalink/t3contribute:cgl-fix-my-commit)

Most PHP coding guidelines can be automatically applied with the command:

```bash
Build/Scripts/runTests.sh -s cgl
```

## JavaScript {#appendix-cgl-javascript}

The following rules should be applied for JavaScript:
[Airbnb JavaScript Style Guide](https://github.com/airbnb/javascript)

## TypeScript {#appendix-cgl-typescript}

The following rules should be applied for TypeScript:
[Excel Micro TypeScript Style Guide](https://github.com/excelmicro/typescript).

## Xliff files {#appendix-cgl-xliff}

Language files are usually stored in a Folder Resources/Private/Language
in files with the ending *.xlf*. Xliff files are indented using 2 spaces.
The following command normalizes your XLIFF files:

```bash
Build/Scripts/runTests.sh -s normalizeXliff
```

Please also check [Xliff / language files](https://docs.typo3.org/permalink/t3contribute:common-review-checks-xlf) for
Xliff-specific things
to pay attention to.

### XLIFF file naming {#appendix-cgl-xliff-filename}

XLIFF files have historically been named with file names starting with
`locallang_`. Newly introduced XLIFF files should drop the `locallang_`
prefix and only be named according to their purpose, for example
`clipboard.xlf` or `db/tt_content.xlf`. Newly introduced file
names should use **snake_case**.

TCA-related XLIFF files should either be called `db.xlf` or be stored in a
folder named `db`, for example `db/tt_content.xlf`.

### Label reference naming {#appendix-cgl-xliff-reference}

Newly introduced label references should use *snake case*. Different parts of a
label reference can be separated by dots, for example:

```xml
<trans-unit id="my_field.title">
    <source>My title</source>
</trans-unit>
<trans-unit id="my_field.description">
    <source>My description</source>
</trans-unit>
```

Existing labels should not be mass-changed to snake case, as each changed label
must be retranslated into all languages.

### Utilizing "translation domain syntax" {#appendix-cgl-xliff-domain-syntax}

With [Feature: #93334 - Translation Domain Mapping](https://docs.typo3.org/c/typo3/cms-core/main/en-us/Changelog/14.0/Feature-93334-TranslationDomainMapping.html#feature-93334-1729000000)
and [Feature: #107759 - TranslateViewHelper supports translation domain syntax](https://docs.typo3.org/c/typo3/cms-core/main/en-us/Changelog/14.0/Feature-107759-TranslateViewHelperSupportsTranslationDomainSyntax.html#feature-107759-1729433323)
the label localization within Fluid template files and PHP code can be
shortened:

```html
<f:translate key="form.legend" domain="core.messages" />
<f:translate key="module.title" domain="core.module" />
```

```php
$languageService->sL('backend.toolbar:save');
```

This syntax is preferred and should be utilized for any new code committed
to TYPO3 v14+ because of these reasons:

-   It is shorter, easier to read, has no odd `LLL:EXT:` magic notation
-   Applies conventions of Symfony translation usage in other frameworks
-   Allows better automatic extraction and analysis (CLI commands)
-   Allows for better deprecations and usage analysis

Detailed reasons are found in the mentioned changelogs.