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When PHP was created 20 years ago, developers loved its simplicity and how well it blended HTML and dynamic code. But as time passed, other template languages - like Twig - were created to make templating even better.

Best Practice

Use Twig templating format for your templates.

Generally speaking, PHP templates are more verbose than Twig templates because they lack native support for lots of modern features needed by templates, like inheritance, automatic escaping and named arguments for filters and functions.

Twig is the default templating format in Symfony and has the largest community support of all non-PHP template engines (it’s used in high profile projects such as Drupal 8).

Template Locations

Best Practice

Store the application templates in the templates/ directory at the root of your project.

Centralizing your templates in a single location simplifies the work of your designers. In addition, using this directory simplifies the notation used when referring to templates (e.g. $this->render('admin/post/show.html.twig') instead of $this->render('@SomeTwigNamespace/Admin/Posts/show.html.twig')).

Best Practice

Use lowercased snake_case for directory and template names.

This recommendation aligns with Twig best practices, where variables and template names use lowercased snake_case too (e.g. user_profile instead of userProfile and edit_form.html.twig instead of EditForm.html.twig).

Best Practice

Use a prefixed underscore for partial templates in template names.

You often want to reuse template code using the include function to avoid redundant code. To determine those partials easily in the filesystem you should prefix partials and any other template without HTML body or extends tag with a single underscore.

Twig Extensions

Best Practice

Define your Twig extensions in the src/Twig/ directory. Your application will automatically detect them and configure them.

Our application needs a custom md2html Twig filter so that we can transform the Markdown contents of each post into HTML. To do this, create a new Markdown class that will be used later by the Twig extension. It just needs to define one single method to transform Markdown content into HTML:

namespace App\Utils;

class Markdown
    // ...

    public function toHtml(string $text): string
        return $this->parser->text($text);

Next, create a new Twig extension and define a filter called md2html using the Twig\TwigFilter class. Inject the newly defined Markdown class in the constructor of the Twig extension:

namespace App\Twig;

use App\Utils\Markdown;
use Twig\Extension\AbstractExtension;
use Twig\TwigFilter;

class AppExtension extends AbstractExtension
    private $parser;

    public function __construct(Markdown $parser)
        $this->parser = $parser;

    public function getFilters()
        return [
            new TwigFilter('md2html', [$this, 'markdownToHtml'], [
                'is_safe' => ['html'],
                'pre_escape' => 'html',

    public function markdownToHtml($content)
        return $this->parser->toHtml($content);

And that’s it!

If you’re using the default services.yaml configuration, you’re done! Symfony will automatically know about your new service and tag it to be used as a Twig extension.

Next: Forms

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.