TYPO3 CMS has a clean bootstrapping process driven mostly by class \TYPO3\CMS\Core\Core\Bootstrap. This class contains a host of methods each responsible for a little step along the initialization of a full TYPO3 process, be it the backend or other contexts.

Some contexts add their own bootstrap class (like the command line, which additionally requires \TYPO3\CMS\Core\Core\CliBootstrap).


The frontend's bootstrapping process is not yet fully encapsulated in a bootstrap class.


This bootstrapping API is internal and may change at any time in the near future even in minor updates. It is thus discouraged to use it in third party code. Use this class only if other extensibility possibilities such as Hooks, Signals or XCLASS are not enough to reach your goals.

One can see the bootstrapping process in action in file typo3/sysext/backend/Classes/Http/Application.php:

use TYPO3\CMS\Core\Core\Bootstrap;


$this->bootstrap = Bootstrap::getInstance()
   ->setRequestType(TYPO3_REQUESTTYPE_BE | (!empty($_GET['ajaxID']) ? TYPO3_REQUESTTYPE_AJAX : 0))

// Redirect to Install Tool if base configuration is not found
if (!$this->bootstrap->checkIfEssentialConfigurationExists()) {

foreach ($this->availableRequestHandlers as $requestHandler) {



Note that most methods of the Bootstrap class must be called in a precise order. It is perfectly possible to define one's own bootstrapping process, but care should be taken about the call order.

Also note that all bootstrapping methods return the instance of the Bootstrap class itself, allowing calls to be chained.


Whenever a call to TYPO3 CMS is made, the application goes through a bootstrapping process managed by a dedicated API. This process is also used in the frontend, but only the backend process is described here.


This chapter is outdated and should probably be merged with the "HTTP request library / Guzzle / PSR-7" chapter below. The chapter should include an overview of single bootstrap steps, PSR-15 and routing.

Classes involved in the backend bootstrapping process are \TYPO3\CMS\Core\Core\Bootstrap and TYPO3\CMS\Backend\Http\Application.

The following steps are performed during bootstrapping.

1. Define legacy constants

In Application::defineLegacyConstants some constants are defined, which will eventually be dropped, but are still initialized for now.

2. Initialize class loader

This defines which autoloader to use.

3. Set request type

The request type is set - this defines whether the current request is a frontend, backend, cli, ajax or Install Tool request. (see defineTypo3RequestTypes).

4. Perform base setup

An instance of \TYPO3\CMS\Core\Core\SystemEnvironmentBuilder is created. This class in turn defines a large number of constants and global variables. If you want to have an overview of these base values, it is worth taking a look into the following methods:

  • SystemEnvironmentBuilder::defineBaseConstants() defines constants containing values such as the current version number, blank character codes and error codes related to services.
  • SystemEnvironmentBuilder::definePaths() defines constants containing paths to various parts of the TYPO3 installation like the absolute path to the typo3 directory or the absolute path to the installation root.
  • SystemEnvironmentBuilder::checkMainPathsExist() checks if expected paths like typo3 or index.php exist. If that is not the case, the process will quit immediately.
  • SystemEnvironmentBuilder::initializeGlobalVariables() sets some global variables as empty arrays.
  • SystemEnvironmentBuilder::initializeGlobalTimeTrackingVariables() defines special variables which contain, for example, the current time or a simulated time as may be set using the Admin Panel.
  • SystemEnvironmentBuilder::initializeBasicErrorReporting() sets up default error reporting level during the bootstrapping process.

5. Define class loading information

This part of the bootstrap processes all the information available to be able to determine where to load classes from, including class alias maps which are used to map legacy class names to new class names.

6. Check essential configuration

In this step we check if crucial configuration elements have been set. If that is not the case, the installation is deemed incomplete and the user is redirected to the Install Tool.

7. Register request handlers

The backend recognizes various request handlers, one to handle general requests, one for backend module requests, one for cli requests and one for AJAX requests.

8. More configuration

Next Bootstrap::configure() is called which in turn triggers a whole new series of configuration. This is actually a major step, with too many actions to detail efficiently here. However here is the list of the most important stuff happening at this point:

  • the main configuration ("TYPO3_CONF_VARS") is loaded
  • the Caching Framework and the Package Management are set up
  • all configuration items from extensions are loaded
  • the database connection is established

9. Dispatch

After all that the Application::run() method is called, which basically dispatches the request to the right handler.

10. Initialization of the TYPO3 Backend

The backend request handler has its own boot() method, which performs yet more initialization and set up as needed. A general request to the backend will typically go through such important steps like:

  • checking backend access: Is it locked? Does it have proper SSL setup?
  • loading the full TCA
  • verifying and initializing the backend user

Application Context

Each request, no matter if it runs from the command line or through HTTP, runs in a specific application context. TYPO3 CMS provides exactly three built-in contexts:

  • Production (default) - should be used for a live site
  • Development - used for development
  • Testing - is only used internally when executing TYPO3 core tests. It must not be used otherwise.

The context TYPO3 runs in is specified through the environment variable TYPO3_CONTEXT. It can be set on the command line:

# run the TYPO3 CMS CLI commands in development context
TYPO3_CONTEXT=Development ./typo3/cli_dispatch.phpsh

or be part of the web server configuration:

# In your Apache configuration, you usually use:
SetEnv TYPO3_CONTEXT Development

# Set context with mod_rewrite
# Rules to set ApplicationContext based on hostname
RewriteCond %{HTTP_HOST} ^dev\.example\.com$
RewriteRule .? - [E=TYPO3_CONTEXT:Development]

RewriteCond %{HTTP_HOST} ^staging\.example\.com$
RewriteRule .? - [E=TYPO3_CONTEXT:Production/Staging]

RewriteCond %{HTTP_HOST} ^www\.example\.com$
RewriteRule .? - [E=TYPO3_CONTEXT:Production]
# In your Nginx configuration, you can pass the context as a fastcgi parameter
location ~ \.php$ {
   include         fastcgi_params;
   fastcgi_index   index.php;
   fastcgi_param   TYPO3_CONTEXT  Development/Dev;
   fastcgi_param   SCRIPT_FILENAME  $document_root$fastcgi_script_name;

Custom Contexts

In certain situations, more specific contexts are desirable:

  • a staging system may run in a Production context, but requires a different set of credentials than the production server.
  • developers working on a project may need different application specific settings but prefer to maintain all configuration files in a common Git repository.

By defining custom contexts which inherit from one of the three base contexts, more specific configuration sets can be realized.

While it is not possible to add new "top-level" contexts at the same level like Production and Testing, you can create arbitrary sub-contexts, just by specifying them like <MainContext>/<SubContext>.

For a staging environment a custom context Production/Staging may provide the necessary settings while the Production/Live context is used on the live instance.


This even works recursively, so if you have a multiple-server staging setup, you could use the context Production/Staging/Server1 and Production/Staging/Server2 if both staging servers needed different configuration.


Testing Is reserved for internal use when executing TYPO3 core functional and unit tests It must not be used otherwise. Instead sub-contexts must be used: Production/Testing or Development/Testing

Usage Example

The current Application Context is set very early in the bootstrap process and can be accessed through public API for example in the AdditionalConfiguration.php file to automatically set different configuration for different contexts.

In file typo3conf/AdditionalConfiguration.php:

switch (\TYPO3\CMS\Core\Utility\GeneralUtility::getApplicationContext()) {
   case 'Development':
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['displayErrors'] = 1;
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['devIPmask'] = '*';
   case 'Production/Staging':
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['displayErrors'] = 0;
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['devIPmask'] = '192.168.1.*';
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['displayErrors'] = 0;
      $GLOBALS['TYPO3_CONF_VARS']['SYS']['devIPmask'] = '';