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HOWTOs / Setting Up Bolt Sites to be Easily Extendable

Note: You are currently reading the documentation for Bolt 3.4. Looking for the documentation for Bolt 3.5 instead?

When you first start on a project with Bolt it's generally quite easy to customise most frontend and even backend features to behave how you need it to. Inevitably though throughout the build and even continuous lifecycle of a project you'll get requests for features or behaviours to be added that can't be done with an out-of-the-box install.

There is the extension marketplace where Bolt users share features to enhance Bolt but if you can't find exactly what you need then it's often essential to add your own customisations.

Since version 3.4 Bolt has made it much easier to do this with the addition of Bundles which are small extensions that sit locally on your project without needing to be submitted to the public extensions marketplace.

There's a very simple process that everyone can take to make it much easier to add this custom functionality to a project and it's often best to do this at the start of a project so it's easy to add extra features as you go along.

Step 1: Use the Bolt Composer install package

With each new release of Bolt there's also an update to the composer install package so installing via this process is the best way to ensure your project structure is correct. All you need to do from a command-line is run:

composer create-project bolt/composer-install:^3.5 <MYPROJECT> --prefer-dist

3.4 is the current latest release but you can change that as each new release is made. Also change <MYPROJECT> to the name of your project, Bolt will then install a new project in the current directory named whatever you setup there.

Step 2. Create a Bolt Configuration File

Bolt looks for a file named .bolt.yml in the root of your project where you can define extensions and other adjustments to Bolt's default behaviour. If you don't already have this then create it.

Step 3. Enable the Customisation Bundle

If you installed Bolt via the composer install method then you just need to add this to your empty .bolt.yml file.

    - Bundle\Site\CustomisationExtension

This tells Bolt that you are going to add custom functionality to the file located in src/Site/CustomisationExtension.php. At the moment that file is empty but in the future we will be able to add custom code in there.

Step 4. Make your own Application class

This may not be necessary for all projects but for more experienced developers it's always good to remember that Bolt can be used as a dependency of your main application, just as Bolt extends a Silex application and adds functionality on top, you can extend Bolt and add any custom behaviour you like. You can also add a custom Application class to your Bolt config too, here's the steps to do it.

First create your application class, make an empty file at src/Site/Application.php

In that file put the following code:


namespace Bundle\Site;

use Bolt\Application as Bolt;

class Application extends Bolt

Secondly open up your .bolt.yml file and add this new section underneath where we previously defined our extensions.

application: Bundle\Site\Application

That's all there is to it, obviously now our custom Application class does not do anything on top of what Bolt does, but we now have the structure setup to change it in the future.

Step 5. Overriding the Frontend Controller

A common request is to add an extra page or URL to the site that does some custom functionality that can't be handled in a Bolt page. As with the application class above, if we swap out the default controller for our own class, then we can easily add our own controller actions. For more advanced developers this also allows you to override the default behaviour of Bolt's built-in actions.

Firstly we create an empty controller class at src/Site/FrontendController.php

Inside that file use the following code:


namespace Bundle\Site;

use Bolt\Controller\Frontend as BoltController;

class FrontendController extends BoltController {


Again, at this stage our controller is empty but in the future we will be able to add our own behaviours into this class.

Finally we need to tell Bolt to use our controller rather than the built-in one, to do this we go back to the custom Application class we created in the step above. Open up the file at src/Site/Application.php and update it to look like this:


namespace Bundle\Site;

use Bolt\Application as Bolt;

class Application extends Bolt
    public function initProviders()
        $this['controller.frontend'] = $this->share(
            function () {
                return new FrontendController();

You will see we've added a new method that overrides Bolt's default initProviders() method.

All we do is call the parent method so the default providers all still get loaded, then after Bolt has set itself up, we jump in and overwrite the controller.frontend service to point to our own controller instead.

You can do this for any Built-in Bolt service but that is something you can explore in the future.

How to Use Your New Extendable Structure

Finally here's a couple of simple examples of how to do basic additions. Firstly we'll add a new custom page to our site that sits outside of Bolt.

In routing (`app/config/routing.yml) add this:

    path: /hello-world
        _controller: controller.frontend:helloWorld

and then add this inside the body of the class in src/Site/FrontendController.php

    public function helloWorld(Request $request)
        return new Symfony\Component\HttpFoundation\Response('<h1>Hello World!<h1>');

Now you can visit http://yoursite.com/hello-world and see your new custom page.

It's worth remembering that now you have your extension class defined you can use it to do all the things described in the documentation, the basics are here and some slightly more advanced ideas are discussed in the intermediate section.

For this example we'll make a new Twig filter, in our templates we sometimes want to really shout about our content so we want a filter that we can use like this: {{ record.title|shout }} which will turn Our Latest News into OUR LATEST NEWS!!

All we need to do is add a couple of methods to our Customisation class. Open the file at src/Site/CustomisationExtension.php and adjust it to look like this:


namespace Bundle\Site;

use Bolt\Extension\SimpleExtension;

class CustomisationExtension extends SimpleExtension
    protected function registerTwigFilters()
        return [
            'shout' => 'shoutFilter',

    public function shoutFilter($text) 
        return strtoupper($text) . '!!';


That's all you need to do in order to get your basic Twig filter working, now go into a Bolt template and start making your content louder.

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