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Host Header

Specifies the target host and port of the resource being requested.

Header TypeRequest Header
SpecificationStandard RFC compliant
Associated CodesHTTP 400,HTTP 421

What is the Host header?

The Host request header names the domain (and optional port) of the server the request targets. It is mandatory in HTTP/1.1: every request must include exactly one Host header so the server knows which host the client intends to reach.

API Usage & Best Practices

  • Enables virtual hosting: Multiple domains can share one IP address because Host disambiguates which site or API the request is for.
  • Missing or duplicate values fail: An HTTP/1.1 request without a Host, or with more than one, must be answered with 400 Bad Request.
  • Ties to 421: If a server receives a request for a host it cannot serve on that connection, it may respond with 421 Misdirected Request.

Examples

GET /v1/users HTTP/1.1
Host: api.example.com:443

Associated HTTP Status Codes

HTTP 400 — Bad Request

The server cannot process the request due to client error (e.g., malformed syntax, invalid framing).

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HTTP 421 — Misdirected Request

The request was directed at a server that is not able to produce a response.

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