What is HTTP Proxy?
An HTTP proxy is a server that forwards HTTP requests on a client's behalf, parsing the protocol rather than blindly relaying bytes. The client sends the full target URL in the request line, or issues a CONNECT to tunnel an HTTPS session. Proxies conventionally listen on ports such as 8080 or 3128; port 80 belongs to the origin web server.
Two request shapes cover almost everything. For plaintext HTTP the client sends an absolute-form request line, GET http://example.com/page HTTP/1.1, along with a Host header, and the proxy resolves the name, opens its own connection to the origin and returns the response. For HTTPS the client sends CONNECT example.com:443 HTTP/1.1, the proxy answers 200 Connection Established, and from that point it relays raw bytes in both directions. TLS is negotiated end to end through that tunnel, so the proxy learns the hostname and the byte counts, nothing of the content.
Authentication is part of the protocol. A proxy that requires credentials answers 407 Proxy Authentication Required with a Proxy-Authenticate header, and the client retries carrying Proxy-Authorization, usually Basic with base64 of user:password. The 407 and the more familiar 401 are different failures - one is the proxy refusing you, the other is the destination site - and confusing them sends people debugging the wrong hop. Providers commonly allow IP allowlisting instead, where the proxy accepts any request from a registered source address and sends no header.
Because it understands HTTP, the proxy can also add to it. Transparent and anonymous proxies append Via and X-Forwarded-For headers that disclose the original client address or the fact that a proxy is in the path, while elite proxies pass the request through without those additions. Some intermediaries insert the legacy Proxy-Connection header. Any of this is visible to the destination, which is why anonymity checkers exist. They report which headers arrived and whether your real address came with them.
The protocol boundary is where an HTTP proxy stops. It handles HTTP and, via CONNECT, tunnels TCP to whatever ports it permits, which is often only 443. SOCKS5 sits lower and relays arbitrary TCP plus UDP association, so anything that is not HTTP-shaped belongs there. One more caveat is the hop between client and proxy, which stays plaintext unless the proxy itself terminates TLS, so Basic credentials on an untrusted network are readable by anyone on the path.
Where you meet it
You configure one constantly without thinking about it: curl -x http://user:pass@host:8080, the http_proxy and https_proxy environment variables, Chrome's --proxy-server flag, or the proxy fields in Scrapy and Playwright. The https_proxy variable trips people up, since it names the proxy used for https:// URLs rather than implying the connection to the proxy is encrypted. When requests fail, read the status code first - a 407 is your credentials, a 403 is the destination.
Common questions
Is traffic through an HTTP proxy encrypted?
The link to the proxy is not, unless the proxy speaks TLS itself. For an https:// destination the client opens a CONNECT tunnel and negotiates TLS with the origin server, so the page content stays encrypted and the proxy only learns the hostname and port. Plain http:// traffic passes through readable, headers and body included.
What port does an HTTP proxy run on?
There is no reserved port. Common conventions are 8080, 3128 and 8888, and commercial providers assign their own, frequently in high ranges. Port 80 is the default for web servers rather than for proxies, so a plan listing 80 is describing the destination protocol, not the port you should connect to.
HTTP proxy or SOCKS5, which should I use?
Use HTTP when your traffic is web traffic and you want the proxy to read headers or apply per-URL rules. Use SOCKS5 when you need arbitrary TCP, UDP, or a protocol the proxy should not interpret. Many providers expose the same endpoint on both, differing only by port number.
Related terms
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