Keep-Alive header
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 number of requests.
NOTE: For
Keep-Aliveto 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-Aliveare 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](https://developer.mozilla.org/en-US/docs/Glossary/Request%20header), [Response header](https://developer.mozilla.org/en-US/docs/Glossary/Response%20header) |
|---|---|
| [Forbidden request header](https://developer.mozilla.org/en-US/docs/Glossary/Forbidden%20request%20header) | Yes |
Syntax
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
timeoutseconds, but the host should attempt to retain a connection for at leasttimeoutseconds.
- : 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
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.
- : An integer that is the maximum number of requests that can be sent on this connection before closing it.
Unless
- : A comma-separated list of parameters, each consisting of an identifier and a value separated by the equal sign (
Examples
A response containing a Keep-Alive header:
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)