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Extending / Custom Bootstrapping

Note: You are currently reading the documentation for Bolt 3.7. Looking for the documentation for Bolt 5.2 instead?

Whilst Bolt is designed to be simple for anyone to install, its core functionality is also modular and easy to configure for developers who are comfortable making a few modifications to how Bolt is bootstrapped.

The basics of configuring a Bolt application

There are two ways your Bolt application is used, via web requests and via the command line with nut. Because there are two entry points, bootstrap configuration/customization needs to be done in a standard place.

This is with a configuration file in the root directory of your project. This file can be either .bolt.yml or .bolt.php. With this file you can modify things like paths, the application class to use, add other services used by the application, and add custom extensions.

Bolt looks for .bolt.yml first, then .bolt.php. The YAML file is recommended, but PHP can be used if programmatic logic is required.

Customising file system paths

Below are full examples of all available paths customised.

Example 1a. YAML .bolt.yml file

    cache: %app%/cache
    config: %app%/config
    database: %app%/database
    extensions: %site%/extensions
    extensions_config: %config%/extensions
    web: %site%/public
    files: %web%/files
    themes: %web%/theme
    bolt_assets: %web%/bolt-public

Example 1b. PHP .bolt.php file


return [
    'paths' => [
        'cache'             => '%app%/cache',
        'config'            => '%app%/config',
        'database'          => '%app%/database',
        'extensions'        => '%site%/extensions',
        'extensions_config' => '%config%/extensions',
        'web'               => '%site%/public',
        'files'             => '%web%/files',
        'themes'            => '%web%/theme',
        'bolt_assets'       => '%web%/bolt-public/view',

Adding your own service providers

Adding your own service provider gives a lot of scope to add your own services or replace/extend any existing service.

Note: Bolt does call Composer's autoloader before this file, but it is up to you to configure composer.json to autoload these classes.

# .bolt.yml
    - MyApp\Provider\CustomProvider
<?php // .bolt.php

return [
    'services' => [
        // or
        new MyApp\Provider\CustomProvider()

Custom Application Class

The Application class can be changed here as well. This allows you to modify Bolt services or add your own, although using the services described above is recommended instead.

In YAML, you can give the class name and we will create it for you. We will still apply any other customization afterwards as well.

application: My\Application

In PHP, you can give the class name...


return [
    'application' => My\Application::class,

For even more flexibly you can create the application yourself, or pull it in from another bootstrap file you have. It’s important to note here that if you give us an application object we'll assume it is ready to go. This means you will need to apply any other customizations yourself.


// Create the application.
$app = new My\Application();

return [
    'application' => $app

// You can also just return the application object as a shortcut
return $app;

Mounting Bolt on an existing application

A lot of work has been done on the internals of Bolt which allow it now to run as a self- contained HTTPKernelInterface application without interfering with any of the global namespace or constants. So if you use StackPHP (or similar) you can mount Bolt onto a URL prefix as simply as this:

// Assuming this is in public/index.php and Bolt is located in vendor/bolt/bolt/
$map = [
    '/another' => new AnotherApplication(),
    '/blog'    => require __DIR__ . '/../vendor/bolt/bolt/app/bootstrap.php'
$app = (new Stack\Builder())
    ->push('Stack\UrlMap', $map)


This means that you can, for instance, use Bolt to manage one specific part of a larger application set.

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