Dries Buytaert

Explanation

max-age specifies the maximum amount of seconds a page is considered valid. The higher max-age, the longer a page can be cached.
Notice A max-age of 30 seconds is short, especially if your content doesn't change frequently. Consider increasing max-age unless the URL has live updates.

The Content Security Policy (CSP) header helps prevent cross-site scripting (XSS), clickjacking, and other code injection attacks by specifying which dynamic resources are allowed to load.
frame-ancestors defines what parents may embed a page using <frame>, <iframe>, <object>, <embed> or <applet>.
Notice Consider adding the upgrade-insecure-requests directive to automatically upgrade HTTP requests to HTTPS, helping to prevent mixed content issues.

The Strict-Transport-Security header (HSTS) instructs browsers to only use HTTPS for future connections to this domain, enhancing security by preventing downgrade attacks and cookie hijacking.
max-age specifies the time, in seconds, that the browser should remember to use HTTPS only for this domain.
includesubdomains instructs the browser that all subdomains are HTTPS-only as well.
preload recommends the domain for inclusion in browsers' preload lists. If accepted, the domain would get hardcoded into browsers as HTTPS-only.

The type of the message body, specified as a MIME type.

The Vary header specifies a list of headers that must be considered when caching responses. For a cached response to be used, these headers must match between the cached response and the new request. This ensures that the appropriate version of a resource is served based on factors like language, encoding, or device type.

Some of the software used to generate or serve this page.

A cookie that was sent from the server to the browser.
path= indicates the path that must exist in the requested URL for the browser to send the cookie.
secure instructs the browser to only send the cookie back when HTTPS requests are used, making it more resistant to man-in-the-middle attacks.

A unique identifier that changes every time a page at a given URL changes. It acts as a fingerprint. A cache can compare Etag values to see if the page has changed and became stale. For example, a browsers will send the ETag value of a cached page in an If-None-Match header. The web server compares the ETag value sent by the browser with the ETag value of the current version of the page. If both values are the same, the web server sends back a 304 Not Modified status and no body.

The date and time at which the request was made. A browser uses it for age calculations rather than using its own internal date and time; e.g. when comparing against Max-Age or Expires.

missing Add a Referrer-Policy header. When a visitor navigates from one page to another, browsers often pass along referrer information. The Referrer-Policy header controls how much referrer information a browser can share. This is important to configure when private information is embedded in the path or query string and passed onto an external destination.

missing Add a Permissions-Policy header. Restrict access to device features like the camera, microphone, location, accelerometer and much more.

missing Add a Cross-Origin-Embedder-Policy to specify how this page can be loaded by cross-origin resources.

missing Add a Cross-Origin-Opener-Policy header to opt-in into better browser isolation.

missing Add a Cross-Origin-Resource-Policy header to specify who can load this page.

missing Add a X-Permitted-Cross-Domain-Policies header to prevent Flash, Adobe Reader and other clients from sharing data across domains.