Dries Buytaert

Explanation

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.

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

public means the response may be stored by all caches, including browser caches, CDNs, and shared caches.
max-age specifies the maximum amount of seconds a page is considered valid. The higher max-age, the longer a page can be cached.
stale-while-revalidate instructs the browser to accept a stale response, while asynchronously checking in the background for a fresh one. The value is the number of seconds the client will accept a stale response for.
stale-if-error instructs the browser to accept a stale response if the check for a fresh one fails. The value is the number of seconds the browser will accept a stale response for. This is good for reliability; e.g. when the origin goes down.

Specifies the page's intended audience. For example, en-US means that the document is intended for English language speakers in the United States. The language tags are defined in RFC 5646.

The X-Content-Type-Options header, when set to nosniff, prevents MIME type sniffing. This enhances security by ensuring browsers respect the declared Content-Type of the response, mitigating MIME confusion attacks.
The value nosniff is correctly set, providing protection against MIME type sniffing attacks.

X-Frame-Options prevents this URL from being embedded in an iframe. This protects against clickjacking attacks.
sameorigin means that this page can be displayed in a iframe, but only on the currrent origin. It can't be displayed on another domain. Consider setting this to deny for added security.

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.

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.

When a visitor navigates from one page to another page, browsers often pass along referrer information. The Referrer-Policy header controls how much referrer information a browser can share. This is important because private information can be embedded in the path or query string.
same-origin means that the protocol, host, port, path and query string are shared for same-site requests. For cross-site requests, nothing is shared.

Instructs a browser to selectively allow or deny certain browser APIs and features. It helps improve security.

This header enables the browser's built-in XSS protection. However, it's considered legacy and modern browsers may ignore it.
1 enables the browser's cross-site scripting (XSS) filtering.
mode=block instructs the browser to block the response if a XSS attack is detected, instead of sanitizing the page.

Instructs clients like Flash and Acrobat Reader what cross-domain policy they have to use. none is the most secure setting. Data can't be shared across domains.

The Cross-Origin-Resource-Policy header is part of the Fetch metadata request headers. It controls how resources can be shared across origins, enhancing security by preventing unauthorized access to resources.
Notice cross-origin means the resource can be loaded by documents from any origin. This is the least secure option.

A Cross-Origin Opener Policy (COOP) header specifies how this page's browsing context can be shared when opened in a 'browser tab', 'popup', 'iframe', etc. The policy can force the creation of a new top-level browsing context to make sure the browser context is protected or isolated.
same-origin specifies that the page can only share the browsing context with other pages from the same origin.

Specifies if this page can embed cross-origin resources. Allowing an attacker to embed a page and load its context into their memory space could result in data leaks. This header shifts the default behavior to an explicit opt-in model; the actual policy is specified in either a seperate Cross-Origin-Resource-Policy header or a CORS check.
Notice unsafe-none means protection is disabled. This page can embedded any cross-origin resource. This is often required to embed things like YouTube videos.

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.
default-src sets the default policy for fetching resources like JavaScript, images, CSS, fonts, AJAX requests, frames, HTML5 media.
base-uri defines what URLs can be used in the <base> URL.
upgrade-insecure-requests instructs browsers to replace insecure URLs (HTTP) with secure URLs (HTTPS).

The page was not served from Drupal's page cache.

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. This particular Etag value starts with w/ which means that it is a weak identifier; while unlikely, multiple pages might have the same identifier. Weak identifiers are used because strong identifiers can be difficult and costly to generate.

When Acquia Cloud receives a web request, it assigns each request a unique request ID and preserves that request ID across different log files.

The type of Acquia Cloud environment that generated this page; could be a production, development, or staging environment.

The time in seconds that the page has been in the shared proxy cache. The maximum age is set by max-age or s-maxage in the Cache-Control header.

The Via header tracks how a page is forwarded from proxy to proxy. Beware, not all proxies append themselves to the Via header.
Notice The Via header uses an incorrect format. Each proxy needs to specify the version of the HTTP protocol used (e.g. varnish/1.1).

The page was served from a cache.

The number of times this page has been served from the Varnish cache. Higher numbers are better.

The page was served from Cloudflare's cache.

The cf-ray header provides a unique identifier for each request through Cloudflare. It's useful for troubleshooting and tracking requests in Cloudflare logs.