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.

Identifies the software used by the origin server to handle the request (e.g. Apache, Nginx, Cloudflare).
Notice Consider removing or minimizing the Server header. Even without a version number, it reveals the server software, which aids reconnaissance.

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 caches to serve a stale response while asynchronously checking in the background for a fresh one. The value is the number of seconds a cache will serve a stale response for.
stale-if-error instructs caches to serve a stale response if the check for a fresh one fails. The value is the number of seconds a cache will serve 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 prevents browsers from guessing a response's content type. Without it, browsers may interpret files differently than intended, which can lead to security vulnerabilities.
The value nosniff is correctly set.

X-Frame-Options prevents this URL from being embedded in an iframe. This protects against clickjacking attacks.
sameorigin allows this page to be displayed in an iframe on the same origin. This is the recommended setting.

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.
strict-origin-when-cross-origin means that the full URL (protocol, host, port, path and query string) is shared for same-origin requests. For cross-origin requests, only the origin (protocol, host, and port) is shared, and only when the protocol security level stays the same or improves (HTTP → HTTP, HTTPS → HTTPS). For cross-origin requests where the protocol downgrades (HTTPS → HTTP), nothing is shared.

Controls which browser features and APIs (camera, microphone, geolocation, payment, USB, etc.) this page and its embedded iframes are allowed to use. Each feature is set to an allowlist of origins; an empty list () disables the feature entirely. This is a defense-in-depth measure: even if an attacker injects script via XSS, they cannot access the restricted APIs.

A legacy header that enables the browser's built-in cross-site scripting (XSS) filter. Modern browsers ignore it in favor of Content-Security-Policy.
1 enables XSS filtering.
mode=block blocks the response entirely if an 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.

Controls which origins are allowed to load this resource (e.g. embed this image, load this script). This prevents other sites from hotlinking your resources and is how a resource signals its consent to be loaded by pages that use Cross-Origin-Embedder-Policy.
Notice cross-origin means the resource can be loaded by documents from any origin. This is the least secure option.

Controls whether other pages can access this page's window object (and vice versa) when opened via window.open() or by navigating to a new page. Without this header, a malicious page could open your site and retain a reference to its window, enabling script-based attacks through the shared browsing context. Setting this to same-origin severs that link for cross-origin pages. Note: COOP governs top-level documents and popups, not iframes. Use X-Frame-Options or CSP frame-ancestors to control iframe embedding.
same-origin isolates this page completely. Cross-origin pages that open this page (or are opened by it) will get window.opener set to null and cannot script each other. This is the strictest and most secure option.

Controls whether this page can load resources (images, scripts, iframes) from other origins. When set, every cross-origin resource must explicitly opt in (via a Cross-Origin-Resource-Policy header or CORS) before this page can load it. This protects those other origins: by requiring their consent, the browser ensures their resources aren't exposed to Spectre-style timing attacks from this page. Setting this header (together with Cross-Origin-Opener-Policy: same-origin) is also required to enable powerful features like SharedArrayBuffer and high-resolution timers.
Notice unsafe-none means protection is disabled. This page can embed any cross-origin resource. This is often required to embed things like YouTube videos. If you don't embed third-party content, use require-corp instead.

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.
script-src specifies valid sources for JavaScript. This includes not only URLs loaded directly into <script> elements, but also things like inline script event handlers (onclick) and XSLT stylesheets which can trigger script execution.
base-uri defines what URLs can be used in the <base> element.
style-src defines what CSS stylesheets are allowed to be loaded.
upgrade-insecure-requests instructs browsers to replace insecure URLs (HTTP) with secure URLs (HTTPS).
Notice unsafe-inline in style-src allows inline styles. This is common and lower risk than inline scripts, but nonces or hashes provide stronger protection.

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

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 not served from a cache.

The page was served from Cloudflare's 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 has become stale. For example, a browser 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.

Specifies how the resource is compressed. Not to be confused with Transfer-Encoding which specifies how the data is transferred.
br means that the data is compressed with brotli.
Warning Add a Content-Length header. The Content-Length header is required, unless the message is transported using chunked encoding. Without a Content-Length header some servers will respond with 400 (bad request) or terminate connections early.

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