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.

private means the response can only be stored by the browser's cache, but not by CDNs, proxies, or any other shared caches.
no-cache means the response can be stored by any cache, but the stored response must be validated with the origin server before each reuse. If the origin confirms that the response hasn't changed, downloading of the full response body can be skipped.
Warning no-cache will cause a revalidation request to the origin server for every use of the cached response. Consider using public with appropriate max-age to improve caching efficiency.
Warning no-store means the response may not be stored in any cache, including the browser's cache. Every request will hit the origin server. If this page can be cached, consider using public with an appropriate max-age.
max-age=0 with must-revalidate means caching is disabled and all requests must be validated with the origin server.
Notice must-revalidate has no effect with no-store since nothing is cached. Remove must-revalidate.
Notice must-revalidate is redundant with no-cache since no-cache already requires revalidation. Remove must-revalidate.
Notice no-cache is redundant when no-store is set, though some sites keep both for compatibility with older caches.
Notice private has no effect when no-store is set since nothing will be cached. It can be safely removed.
Notice pre-check is a legacy directive introduced by Internet Explorer 5 and is no longer supported. No other browser supports it. Including pre-check is unnecessary, wastes bandwidth and processing power.
Notice post-check is a legacy directive introduced by Internet Explorer 5 and is no longer supported. No other browser supports it. Including post-check is unnecessary, wastes bandwidth and processing power.

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.

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.

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 Report-To header defines where browsers should send error reports. It sets up named reporting endpoints that other headers (like NEL and Content-Security-Policy) reference when they need to send violation or failure data.
group defines the reporting group. Groups allow reports to be grouped logically; e.g. there could be a group for network errors and a second group for browser feature deprecation reports.
max_age defines the number of seconds the browser should remember these settings. Prevents the browser from having to parse the JSON on each request.
endpoints defines one or more URLs where the reports need to be sent to. Multiple URLs can be specified for failover and load-balancing. Endpoints can be assigned a weight to distribute load, with each endpoint receiving a specified fraction of the reporting traffic. Endpoints can also be assigned a priority to set up fallback collectors.

The NEL (Network Error Logging) header tells browsers to report network-level failures (DNS errors, TCP timeouts, TLS problems) back to the server. This means you can detect when real users fail to reach your site, even though the failure happens before your server sees a request.
report_to defines the reporting group that reports for this NEL policy will be sent to. The reporting group details are specified in the Report-To header.
max_age defines the number of seconds the browser should remember these settings. Prevents the browser from having to parse the JSON on each request.
success_fraction defines the sampling rate that should be applied to reports about successful network requests. Its value must be a number between 0.0 and 1.0: 0 means no successful requests should be reported, and 1 means that every successful request should be reported.

Specifies how the resource is compressed. Not to be confused with Transfer-Encoding which specifies how the data is transferred.
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.

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.

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

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.

missing Add a Strict-Transport-Security header. The Strict-Transport-Security header or HSTS header is used to instruct browsers to only use HTTPS, instead of using HTTP. It helps enforce secure communication.

missing Add a Content-Security-Policy header. The Content-Security-Policy header helps browsers prevent cross site scripting (XSS) and data injection attacks.

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 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.

missing Add a Cross-Origin-Opener-Policy header. It prevents other sites from retaining a window reference to this page when opened via window.open() or navigation, blocking script-based attacks through shared browsing contexts.

missing Add a Cross-Origin-Resource-Policy header. It controls which origins can embed or load this page's resources (images, scripts, etc.), preventing hotlinking and cross-origin data leaks.

missing Add an X-Content-Type-Options: nosniff header to prevent browsers from MIME type sniffing. Without it, browsers may interpret files as a different content type than intended, which can lead to security vulnerabilities.

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