IAST, or Interactive Application Security Testing, is a security testing method that inspects an application from the inside while it is running. Unlike a static scanner that only reviews source code, or an external DAST tool that probes from the outside, IAST typically uses an in-app agent to observe execution, inputs, and calls to sensitive functions. That runtime visibility helps it identify risky data flows, insecure configuration, and exploitable paths with more context.
IAST matters because it can show how a flaw behaves during real application activity, including during QA traffic or automated tests. Security teams use it to catch issues such as tainted user input reaching a database query, file write, or command execution path. In defense, the value is practical: fewer false positives, better code-path evidence, and easier prioritization for developers. In attacks, the same runtime paths are what adversaries try to abuse, so IAST helps defenders see where input handling and control flow are weak.