Host
The HTTP Host request header specifies the host and port number of the server receiving the request. This header is required in all HTTP/1.1 requests.
Usage
Every HTTP/1.1 request includes a Host header. The header enables virtual hosting, where a single server with one IP address hosts multiple domains. Without Host, the server has no way to determine which domain the client intended to reach.
The value contains the requested hostname and an optional port number separated by a colon. When no port is specified, the default port for the scheme applies: port 80 for HTTP and port 443 for HTTPS.
A server receiving an HTTP/1.1 request without a Host header responds with 400 Bad Request. The same response applies when a request contains more than one Host header, as the ambiguity prevents the server from selecting the correct virtual host.
In HTTP/2 and HTTP/3, the :authority
pseudo-header field replaces Host. Clients sending
HTTP/2 or HTTP/3 requests place the host information in
:authority instead. When a gateway converts an HTTP/2
request to HTTP/1.1, the gateway generates the
Host header from the :authority value.
The Host header differs from the Origin header. Host identifies the target server for every request. Origin identifies the source of a cross-origin request and appears only in specific contexts such as CORS preflight requests and form submissions.
Directives
host
The domain name or IP address of the target server.
port
An optional TCP port number. When omitted, the default port for the request scheme is assumed (80 for HTTP, 443 for HTTPS).
Host: <host>:<port>
Example
A standard HTTPS request to a web server omits the port because 443 is the default for HTTPS.
GET /articles/http-headers HTTP/1.1
Host: example.re
When a server runs on a non-standard port, the port number is included after the hostname.
GET /api/status HTTP/1.1
Host: api.example.re:8443
A request to an IP address includes the address directly. This form is common in development environments and internal services.
GET /health HTTP/1.1
Host: 192.168.1.100:3000
Takeaway
The Host header identifies the target server in every HTTP/1.1 request, enabling virtual hosting on servers with shared IP addresses. The header is mandatory, and requests missing a valid Host value receive a 400 Bad Request response.