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

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.

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.

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.

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.

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.

This Expires date is in the past: the page is considered stale and will be removed from all caches.
Notice Because there is a Cache-Control header with a max-age and/or s-maxage directive, the Expires header will be ignored. Consider removing Expires to save bandwidth and processing power.
PS: November 19th is my birthday! 🎂

The date and time at which the origin server believes the page was last modified.
Notice Because there is an Etag header, Last-Modified is likely to be ignored. The ETag hash is more accurate than the date/time in Last-Modified. Consider removing Last-Modified to save bandwidth and processing power.

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.

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.
object-src defines what <object>, <embed> and <applet> elements are allowed to be loaded and executed.
style-src defines what CSS stylesheets are allowed to be loaded.
img-src defines what images and favicons can be loaded.
font-src defines what fonts can be loaded using CSS's @font-face.
frame-src defines what <frame> and <iframe> elements can be loaded.
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.
Warning unsafe-inline in script-src allows execution of inline scripts, which effectively disables CSP's XSS protection. Consider using nonces or hashes instead.

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.

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 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-allow-popups isolates this page from cross-origin openers (like same-origin), but still allows popups opened by this page to retain a connection if the popup has COOP set to unsafe-none (any origin) or same-origin-allow-popups (same origin only). This is useful for pages that need to interact with OAuth or payment popups.

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.

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.

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 full URL (protocol, host, port, path and query string) is shared for same-origin requests. For cross-origin requests, no referrer information is shared at all.

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.

The page was not served from Amazon CloudFront.

The Via header tracks how a page is forwarded from proxy to proxy. Beware, not all proxies append themselves to the Via header.

Amazon CloudFront's edge servers that were queried for the request. The first 3 letters are an IATA location code.

The alt-svc header tells the browser that the same content is available over a different protocol. This allows the browser to upgrade to a faster protocol (e.g. HTTP/3 over QUIC) on subsequent requests without a separate negotiation step.
h3 indicates that HTTP/3 is supported. HTTP/3 uses the QUIC protocol (UDP-based) instead of TCP, which eliminates the TCP handshake delay and performs better on lossy networks. Variants like h3-29 refer to specific drafts of the HTTP/3 protocol.
ma=86400 specifies that the alternative service information is fresh for 86400 seconds.

A unique request identifier generated by Amazon CloudFront. This ID can be used to troubleshoot the request and trace it through Amazon's network.

missing Add a Cross-Origin-Embedder-Policy header. It requires cross-origin resources to explicitly consent before this page can load them, protecting those resources from being exposed to Spectre-style timing attacks. Together with Cross-Origin-Opener-Policy, it enables cross-origin isolation and access to SharedArrayBuffer.