What is a Content Security Policy? A Content Security Policy (CSP) is an HTTP response header that web servers send to browsers to restrict the sources from which dynamic resources can be loaded and executed. It acts as a set of rules that defines which external domains and local resources are trustworthy. By establishing these boundaries, CSP prevents browsers from running unauthorized scripts, loading suspicious media, or sending sensitive data to unknown external servers. The Analogy: The Factory Quality Control Checklist Think of a highly automated manufacturing plant assembling smartphones. The plant operates on a strict quality control checklist. The assembly machines are programmed to only accept parts that arrive from specific, pre-vetted suppliers: screens from Supplier A, batteries from Supplier B, and chips from Supplier C. If a delivery truck arrives at the factory loading dock with an unbranded crate of batteries, the automated systems recognize that this supplier is ...