PHP lets us set the HTTP headers of a response through the header() function.

HTTP Headers are a way to send information back to the browser.

We can say the page generates a 500 Internal Server Error:

<?php
header('HTTP/1.1 500 Internal Server Error');
?>

Now you should see the status if you access the page with the Browser Developer Tools open:

We can set the content/type of a response:

header('Content-Type: text/json');

We can force a 301 redirect:

header('HTTP/1.1 301 Moved Permanently');
header('Location: https://flaviocopes.com');

We can use headers to say to the browser “cache this page”, “don’t cache this page”, and a lot more!