Skip to main content
apiguide.dev

ETag Header

An identifier for a specific version of a resource, used for cache validation.

Header TypeResponse Header
SpecificationStandard RFC compliant
Associated CodesHTTP 200,HTTP 304,HTTP 412

What is the ETag header?

The ETag (Entity Tag) response header is a unique string hash representing the current state of a resource. If the resource data changes, the ETag changes.

API Usage & Best Practices

  • Saves bandwidth: Clients save the ETag and send it back on subsequent requests in the If-None-Match header. If the data is unchanged, the server responds with 304 Not Modified instead of rebuilding and sending the JSON.
  • Optimistic concurrency: Can be used alongside If-Match to prevent clients from overwriting each other’s edits.

Examples

HTTP/1.1 200 OK
ETag: "w/3a84e27f01"

Associated HTTP Status Codes

HTTP 200 — OK

The request has succeeded. The response payload contains the requested resource representation.

View reference →

HTTP 304 — Not Modified

Instructs the client that the cached version of the resource is still valid.

View reference →

HTTP 412 — Precondition Failed

One or more preconditions in the request headers evaluated to false.

View reference →

Sponsors

Support the project →