WASI

The WebAssembly System Interface (WASI) is a modular, capability-based system interface that extends WebAssembly beyond the browser by providing portable, secure access to operating system primitives — files, clocks, random numbers, and network sockets — without requiring a JavaScript runtime or a full operating system. Unlike POSIX, which grants a process blanket access to the system based on its user identity, WASI grants access to specific resources passed explicitly at module invocation, making it possible to run untrusted Wasm code with fine-grained, auditable permissions. WASI is the decisive step that transforms WebAssembly from a browser technology into a universal computation substrate, and its adoption by cloud providers and edge platforms signals that the future of portable code is not merely about running everywhere, but about running safely everywhere — a distinction that POSIX never quite managed.