Keep-Alive header

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The HTTP Keep-Alive request and response header allows the sender to hint how a connection may be used in terms of a timeout and a maximum amount of requests.

Note: For Keep-Alive to have any effect, the message must also include a Connection: keep-alive header.

HTTP/1.0 closes the connection after each request/response interaction by default, so persistent connections in HTTP/1.0 must be explicitly negotiated. Some clients and servers might wish to be compatible with previous approaches to persistent connections, and can do this with a Connection: keep-alive request header. Additional parameters for the connection can be requested with the Keep-Alive header.

Warning: Connection-specific header fields such as Connection and Keep-Alive are prohibited in HTTP/2 and HTTP/3. Chrome and Firefox ignore them in HTTP/2 responses, but Safari conforms to the HTTP/2 specification requirements and does not load any response that contains them.

Header type Request header, Response header
Forbidden request header Yes

Syntax

http
Keep-Alive: <parameters>

Directives

<parameters>

A comma-separated list of parameters, each consisting of an identifier and a value separated by the equal sign (=). The following identifiers are possible:

timeout

An integer that is the time in seconds that the host will allow an idle connection to remain open before it is closed. A connection is idle if no data is sent or received by a host. A host may keep an idle connection open for longer than timeout seconds, but the host should attempt to retain a connection for at least timeout seconds.

max

An integer that is the maximum number of requests that can be sent on this connection before closing it. Unless 0, this value is ignored for non-pipelined connections as another request will be sent in the next response. An HTTP pipeline can use it to limit the pipelining.

Examples

A response containing a Keep-Alive header:

http
HTTP/1.1 200 OK
Connection: Keep-Alive
Content-Encoding: gzip
Content-Type: text/html; charset=utf-8
Date: Thu, 11 Aug 2016 15:23:13 GMT
Keep-Alive: timeout=5, max=200
Last-Modified: Mon, 25 Jul 2016 04:32:39 GMT
Server: Apache

(body)

Specifications

Specification
HTTP/1.1
# compatibility.with.http.1.0.persistent.connections

Browser compatibility

See also