The HTTP Sec-WebSocket-Accept response header is used in the WebSocket opening handshake to indicate that the server is willing to upgrade to a WebSocket connection.

This header must appear no more than once in the response, and has a directive value that is calculated from the Sec-WebSocket-Key request header sent in the corresponding request.

Syntax

Sec-WebSocket-Accept: <hashed key>

Directives

<hashed key>

If a Sec-WebSocket-Key header was provided, the value of this header is computed by taking the value of the key, concatenating the string 258EAFA5-E914-47DA-95CA-C5AB0DC85B11, and taking the SHA-1 hash of that concatenated string — resulting in a 20-byte value. That value is then base64 encoded to obtain the value of this property.

Examples

WebSocket opening handshake

The client will initiate a WebSocket handshake with a request like the following. Note that this starts as an HTTP GET request (HTTP/1.1 or later) and includes the Upgrade header indicating the intent to upgrade to a WebSocket connection. It also includes Sec-WebSocket-Key, which is used in the calculation of Sec-WebSocket-Accept to confirm the intent to upgrade the connection to a WebSocket connection.

GET /chat HTTP/1.1
Host: example.com:8000
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Sec-WebSocket-Version: 13

The response from the server should include the Sec-WebSocket-Accept header with a value that is calculated from the Sec-WebSocket-Key header in the request, and confirms the intent to upgrade the connection to a WebSocket connection:

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=

Specifications

Browser compatibility

See also

• Sec-WebSocket-Key
• Sec-WebSocket-Version
• Sec-WebSocket-Protocol
• Sec-WebSocket-Extensions
• The WebSocket handshake in Writing WebSocket servers
• HTTP Protocol upgrade mechanism