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HTTP Header
Via
GeneralTracks the intermediate proxies and gateways that forwarded a request or response.
HTTP header reference, syntax, examples, and developer usage.
What is the Via header?
The Via HTTP header is used to transmit metadata between a client and server as part of HTTP requests or responses.
HTTP headers define how content should be interpreted, cached, authenticated, secured, or processed by browsers and APIs.
Direction
This header may appear in both HTTP requests and responses.
Syntax
Via: <protocol> <proxy-host>[, <protocol> <proxy-host>]
Example
Via: 1.1 proxy1.example.com, 2.0 cdn.example.com
Common use cases
- Tracing the path of a request through proxy chains
- Detecting forwarding loops
- Debugging CDN and reverse proxy routing
Common mistakes
- Using the header in the wrong request or response context
- Sending invalid header values
- Incorrect header syntax
- Assuming the header automatically changes server behaviour
Practical developer insight
Via is added by each proxy along the request or response path. It includes the protocol version and the proxy identifier. It is useful for diagnosing multi-hop routing and is required by HTTP spec for proxies. Often seen in CDN responses alongside X-Cache headers.