Response inspection is the analysis of outbound traffic, especially HTTP responses, before they leave a server or security gateway. The goal is to detect unsafe content such as sensitive data leakage, unexpected code injection, reflected payloads, or policy violations in headers and bodies. In a web application firewall, response inspection complements request inspection: one looks at what enters the application, the other checks what comes out.
This matters because attacks do not always begin with a blocked request. An application may process malicious input and then echo it back, expose secrets, or generate a response that helps an attacker refine exploitation. Response inspection can catch those mistakes in real time, support data-loss prevention, and enforce output filtering for HTML, JSON, and file downloads. It is only effective when the security layer parses responses the same way the application and browser do; mismatched encoding, compression, or chunking can create blind spots and let unsafe content pass unnoticed.