--- title: "Bootstrapping" manual: "TYPO3 Explained" version: "main" permalink: "https://docs.typo3.org/permalink/t3coreapi:bootstrapping@main" source: "ApiOverview/RequestLifeCycle/Bootstrapping.rst" rendered: "2026-09-19T06:56:03+00:00" --- # Bootstrapping {#bootstrapping} TYPO3 has a clean bootstrapping process driven mostly by class `\TYPO3\CMS\Core\Core\Bootstrap`. This class is initialized by calling `Bootstrap::init()` and serves as an entry point for later calling an application class, depending on several context-dependant constraints. Each application class registers request handlers to run a certain request type (e.g. eID or Ajax requests in the backend). Each application is handed over the class loader provided by Composer. ## Applications {#bootstrapping-applications} There are four types of applications provided by the TYPO3 Core: ### `\TYPO3\CMS\Frontend\Http\Application` {#bootstrapping-applications-typo3cmsfrontendhttpapplication} This class handles all incoming web requests coming through `index.php` in the public web directory. It handles all regular page and eID requests. It checks if all configuration is set, otherwise redirects to the TYPO3 Install Tool. ### `\TYPO3\CMS\Backend\Http\Application` {#bootstrapping-applications-typo3cmsbackendhttpapplication} This class handles all incoming web requests for any regular backend call inside `typo3/\*`. Its `\TYPO3\CMS\Backend\Http\RequestHandler` is used for all backend requests, including Ajax routes. If a get/post parameter "route" is set, the backend routing is called by the `RequestHandler` and searches for a matching route inside the router. The corresponding controller / action is called then which returns the response. The `Application` checks if all configuration is set, otherwise it redirects to the TYPO3 Install Tool. ### `\TYPO3\CMS\Core\Console\CommandApplication` {#bootstrapping-applications-typo3cmscoreconsolecommandapplication} This class is the entry point for the TYPO3 command line for console commands. In addition to registering all available commands, this also sets up a CLI user. ### `\TYPO3\CMS\Install\Http\Application` {#bootstrapping-applications-typo3cmsinstallhttpapplication} The install tool `Application` only runs with a very limited bootstrap set up. The failsafe package manager does not take the `ext_localconf.php` of installed extensions into account. > [!WARNING] > 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 > [Events](https://docs.typo3.org/permalink/t3coreapi:eventdispatcher@main), [Hooks](https://docs.typo3.org/permalink/t3coreapi:hooks@main), or [XCLASS](https://docs.typo3.org/permalink/t3coreapi:xclasses@main) > are not enough to reach your goals. Example of bootstrapping the TYPO3 Backend: **An entry script bootstrapping the backend** ```php get(Application::class)->run(); }); ``` ## Initialization {#backend-initialization} Whenever a call to TYPO3 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. > [!NOTE] > 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. The following steps are performed during bootstrapping. ### 1\. Initialize the class loader {#backend-initialization-1-initialize-class} This defines which autoloader to use. ### 2\. Run `SystemEnvironmentBuilder` {#backend-initialization-2-run-systemenvironmentbuilder} The `\TYPO3\CMS\Core\Core\SystemEnvironmentBuilder` is responsible for setting up a system environment that is shared by all contexts (FE, BE, Install Tool and CLI). This class 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::defineTypo3RequestTypes()` defines the different constants for determining if the current request is a frontend, backend, CLI, Ajax or Install Tool request. - `SystemEnvironmentBuilder::defineBaseConstants()` defines constants containing values such as the current version number, blank character codes and error codes related to services. - `SystemEnvironmentBuilder::initializeEnvironment()` initializes the `Environment` class that points to various parts of the TYPO3 installation like the absolute path to the `typo3` directory or the absolute path to the installation root. - `SystemEnvironmentBuilder::calculateScriptPath()` calculates the script path. This is the absolute path to the entry script. This can be something like '.../public/index.php' for web calls, or '.../bin/typo3' or similar for CLI calls. - `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. ### 3\. Initialize bootstrap {#backend-initialization-3-initialize-bootstrap} `\TYPO3\CMS\Core\Core\Bootstrap` boots up TYPO3 and returns a container that is later used to run an application. As a basic overview it does the following: - `Bootstrap::initializeClassLoader()` 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. - `Bootstrap::checkIfEssentialConfigurationExists()` checks 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. - `Bootstrap::createConfigurationManager()` creates the Configuration Manager which is then populated with the the main configuration ("TYPO3_CONF_VARS"). - `$builder->createDependencyInjectionContainer()` creates a [dependency injection](https://docs.typo3.org/permalink/t3coreapi:dependency-injection@main) container which is later returned by `Bootstrap::init()`. - The caching framework and the package management are set up. - All configuration items from extensions are loaded - The database connection is established ### 4\. Dispatch {#backend-initialization-4-dispatch} After all that the, the newly created container receives the application object and `Application::run()` method is called, which basically dispatches the request to the right handler. ### 5\. Initialization of the TYPO3 backend {#backend-initialization-5-initialization-typo3} The backend request handler then calls the `MiddlewareDispatcher` which then manages and dispatches a PSR-15 middleware stack. In the backend context this will typically go through such important steps like: - checking backend access: Is it locked? Does it have proper SSL setup? - loading the full [TCA](https://docs.typo3.org/m/typo3/reference-tca/main/en-us/Index.html#start) - verifying and initializing the backend user > [!NOTE] > For more information on the middleware stack, you can continue reading the > chapter [Middlewares (request handling)](https://docs.typo3.org/permalink/t3coreapi:request-handling@main). ## Application context {#bootstrapping-context} Each request, no matter if it runs from the command line or through HTTP, runs in a specific *application context*. TYPO3 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: ```bash # run the TYPO3 CLI commands in development context TYPO3_CONTEXT=Development ./bin/typo3 ``` or be part of the web server configuration: **.htaccess or Apache vhost configuration** ```apacheconf # In your Apache configuration (either .htaccess or vhost) # you can either set context to static value with: SetEnv TYPO3_CONTEXT Development # Or set context depending on current host header # using mod_rewrite module 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] # or using setenvif module SetEnvIf Host "^dev\.example\.com$" TYPO3_CONTEXT=Development SetEnvIf Host "^staging\.example\.com$" TYPO3_CONTEXT=Production/Staging SetEnvIf Host "^www\.example\.com$" TYPO3_CONTEXT=Production ``` **nginx-site-typo3.conf** ```nginx # In your Nginx configuration, you can pass the context as a fastcgi parameter location ~ \.php$ { include fastcgi_params; fastcgi_index index.php; fastcgi_param TYPO3_CONTEXT Development/Dev; fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name; } ``` ### Custom contexts {#bootstrapping-context-custom} 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 `/`. 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. > [!NOTE] > 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. > [!WARNING] > **Attention** > > `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 {#bootstrapping-context-example} The current Application Context is set very early in the bootstrap process and can be accessed through public API for example in the `config/system/additional.php` file to automatically set different configuration for different contexts. In file `config/system/additional.php`: **config/system/additional.php** ```php