The HTTP Accept-Encoding request and response header indicates the content encoding (usually a Compression algorithm) that the sender can understand.
In requests, the server uses content negotiation to select one of the encoding proposals from the client and informs the client of that choice with the Content-Encoding response header.
In responses, it provides information about which content encodings the server can understand in messages to the requested resource, so that the encoding can be used in subsequent requests to the resource.
For example, Accept-Encoding is included in a 415 Unsupported Media Type response if a request to a resource (e.g., PUT) used an unsupported encoding....content encoding (usually a compression algorithm) that the sender...server support the same compression algorithms, the server may...