Understanding ZAP's Proxy Architecture

ZAP functions as an intercepting proxy, positioning itself between your browser and target web applications to capture, analyze, and modify HTTP/HTTPS traffic. This man-in-the-middle position provides complete visibility into application communication, revealing hidden parameters, API calls, and security mechanisms that normal browsing obscures. Understanding this architecture helps leverage ZAP's full potential for manual security testing.

The proxy operates on port 8080 by default, though this is configurable for environments with port conflicts. When configured correctly, every request from your browser passes through ZAP before reaching the target server, and every response returns through ZAP before displaying in your browser. This bidirectional interception enables both passive analysis and active manipulation of web traffic.

Certificate handling for HTTPS interception requires special attention. ZAP generates a root certificate authority (CA) that must be installed in your browser or system certificate store. This certificate allows ZAP to decrypt HTTPS traffic by creating certificates on-the-fly for each secure site you visit. While this breaks the normal SSL/TLS trust model, it's essential for security testing of modern applications that exclusively use HTTPS.