UXP is a cross-application HTML/CSS/JS-based extensibility framework that replaces older CEP (Common Extensibility Platform). Key features:

From Microsoft’s VS Code to Adobe’s own UDT and CLI, every tool you need to build, debug, and ship a high-performance Creative Cloud plugin is available for literally zero dollars. Whether you are automating a tedious export workflow for your design team or building the next must-have extension for millions of designers, the path is open.