What is Proxy Server?
A proxy server is an intermediary that accepts your connection, makes its own request to the destination, and relays the response back. The destination logs the proxy's IP address instead of yours. Proxies are used for anonymity, geographic routing, access control, caching, and spreading a workload across many addresses so no single one is rate limited.
Two arrangements share the name. A forward proxy sits in front of clients and hides them from servers; a reverse proxy sits in front of servers and hides them from clients. Everything a proxy provider sells is the forward kind. An HTTP forward proxy reads the request line and opens its own socket to the origin, then copies bytes in both directions. HTTPS is opaque to it, so the client sends CONNECT host:443 and the proxy becomes a blind TCP tunnel once it answers 200 Connection established.
Configuration is a host and port plus a credential. Conventional ports are 8080 and 3128 for HTTP proxies and 1080 for SOCKS, though providers assign whatever they like. Credentials travel in a Proxy-Authorization header, and a proxy that wants them and does not get them answers 407 Proxy Authentication Required, which is distinct from a 401 raised by the origin server. The alternative is IP allowlisting, where the proxy recognises your server's own address and skips the password. Most command line tools read HTTP_PROXY, HTTPS_PROXY and NO_PROXY from the environment.
What the origin sees depends on how honest the proxy is. Transparent and anonymous proxies attach headers such as Via and X-Forwarded-For that name the intermediary or the original client; an elite proxy adds nothing and looks like an ordinary browser connecting directly. The address is only one signal. Your TLS handshake and your DNS resolution still originate with you unless the proxy resolves hostnames on your behalf, which is where DNS leaks come from. Clients differ here, some passing the hostname to the proxy and others resolving locally and connecting to a bare address.
Failure modes are worth recognising on sight. A 407 means credentials. A 502 or 503 usually means the proxy reached the origin and got nothing usable, or the exit died mid-session, while silent connection resets during CONNECT often mean the target blocked the exit address rather than anything being wrong with the proxy. Certificate warnings tell you the proxy is terminating TLS with its own certificate and reading the plaintext, which is normal for a corporate gateway and disqualifying for anything else.
Where you meet it
You meet a proxy server the first time a target starts returning 403s to your own address, or when a dataset has to be collected from inside a country you are not in. Every scraping framework, HTTP client and antidetect browser has a field for one: scheme, host, port, username, password. Getting that string right, and knowing whether the tool tunnels DNS through it, is most of the work.
Common questions
What is the difference between a forward proxy and a reverse proxy?
A forward proxy acts for the client: you configure it, and it hides your address from the sites you visit. A reverse proxy acts for the server, sitting in front of an origin to terminate TLS and cache responses, invisible to the visitor. Commercial proxy services sell forward proxies.
Does a proxy server encrypt my traffic?
Not on its own. When you request an HTTPS site through a CONNECT tunnel, the encryption runs between your client and the origin, and the proxy passes ciphertext it cannot read. The hop from you to the proxy is protected only if the proxy itself accepts HTTPS connections. SOCKS adds no encryption at all.
Why does my proxy return 407?
407 Proxy Authentication Required means the proxy wants credentials it did not get. Either the username and password are missing or wrong in the proxy URL, or the service expects IP allowlisting and your current outbound address is not on the list. A 401 comes from the destination site instead, not from the proxy.
Related terms
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