YAML is used in TYPO3 for various configurations; most notable are


TYPO3 is using a custom YAML loader for handling YAML in TYPO3 based on the Symfony YAML package. It’s located at \TYPO3\CMS\Core\Configuration\Loader\YamlFileLoader and can be used when YAML parsing is required.

The TYPO3 Core YAML resolves environment variables. Resolving of variables in the loader can be enabled or disabled via flags. For example, when editing the site configuration through the backend interface the resolving of environment variables needs to be disabled to be able to add environment configuration through the interface.

The format for environment variables is %env(ENV_NAME)%. Environment variables may be used to replace complete values or parts of a value.

The YAML Loader class has two flags: PROCESS_PLACEHOLDERS and PROCESS_IMPORTS.

  • PROCESS_PLACEHOLDERS decides whether or not placeholders (%abc%) will be resolved.
  • PROCESS_IMPORTS decides whether or not imports (imports key) will be resolved.

Use the method YamlFileLoader::load() to make use of the loader in your extensions:

use TYPO3\CMS\Core\Configuration\Loader\YamlFileLoader;

// ...

(new YamlFileLoader())->load(string $fileName, int $flags = self::PROCESS_PLACEHOLDERS | self::PROCESS_IMPORTS)