ETag (Entity Tag)
Unique hash or identifier for a specific version of a resource, allowing efficient cache revalidation with 304 Not Modified responses.
W/"33a64df551425fcc55e4d42a148795d9f25f89d4"Production Server Implementation
etag on; # Default in modern NGINX versionsDirectives & Syntax Breakdown
Indicates the resource is semantically equivalent even if byte-by-byte representations differ slightly.
Requires strict byte-for-byte identity matching between client and server copies.
Common Security Hazards & Pitfalls
- •In multi-server load-balanced environments, ensure all server nodes generate identical ETags for identical content.
ETag (Entity Tag) - Questions & Answers
Common implementation questions, browser enforcement rules, and debugging.
When a cached file expires, the browser sends "If-None-Match: <etag>". If unchanged, the server returns a 304 Not Modified with zero body payload.
Related HTTP Headers
Browse All HeadersRestricts where scripts, images, styles, and frames can be loaded from, protecting websites from Cross-Site Scripting (XSS) and data injection attacks.
Forces modern web browsers to communicate exclusively over encrypted HTTPS connections, preventing SSL stripping and man-in-the-middle (MITM) attacks.
Indicates whether a browser should be allowed to render a page inside an <iframe>, <frame>, or <object>, protecting users against clickjacking attacks.
Prevents the browser from MIME-sniffing a response away from the declared Content-Type header, mitigating drive-by malware and MIME confusion attacks.
Controls how much referrer information (URL path and query parameters) is included when navigating away or loading external assets.
Allows site owners to selectively restrict browser hardware features, sensors, APIs, and privacy-invasive tracking mechanisms.