In this episode, we dive into customizing the 404 page for a Slim 3 application. Even though showing a pretty 404 page might seem simple, we go a bit deeper by actually looking at how Slim handles 404 responses under the hood. This way, you'll get a clearer understanding of what's happening when a page isn't found, and how you can take control.
We start with a basic Slim 3 setup and quickly review the project structure. You'll see where the default 404 comes from and how Slim decides when to trigger it. We poke around Slim's core code to uncover how the Not Found Handler works, which helps us figure out the right spot to add in our own handler.
Next, we set up a custom not found handler in our dependency container, showing the right way to return a response and send the correct HTTP status (which is super important for SEO and crawlers). You'll also see how to make a Twig template for your 404 page so your error page feels just like the rest of your site—header, footer, everything.
By the end, you'll have a custom-designed 404 page integrated into your Slim 3 project, complete with the proper status code. This process is super quick once you know where to look, and you'll finish up with a more professional and friendly error experience for your users.