Glossary term
What is ETag (Entity Tag)?
ETag stands for Entity Tag.
In System Design
A fingerprint of a resource's version. Example: "Has this changed since version abc123?" If not → 304 Not Modified.
Learn it properly · System DesignLesson 3: HTTP & HTTPS Explained: Methods, Status Codes and TLSHTTP is the shared language of the web: a method and URL in, a status code and body out. HTTPS wraps it in TLS so nobody on the path can read or change it. Methods, idempotency, status codes, HTTP/1.1 vs 2 vs 3, and the TLS handshake.In The Browser Contract
A fingerprint of a response. The browser sends it back in If-None-Match. If nothing changed, the server replies 304 Not Modified and skips the body.
Learn it properly · The Browser ContractLesson 5: HTTP Caching: Cache-Control, ETags and the CDN in BetweenFresh or must-check, no-cache vs no-store, immutable for hashed files, stale-while-revalidate, and what a shared cache must never store.In API Design
A short label for one version of a resource, which changes when the resource changes.
Learn it properly · API DesignLesson 1: HTTP Methods, Status Codes and Idempotency in PracticeGET, POST, PUT, PATCH and DELETE used correctly, the status codes that matter, and why idempotency decides whether a retry is safe.