workerd

workerd is the server runtime that powers Cloudflare Workers — a modern, standards-aligned JavaScript and WebAssembly execution environment that can be run outside of Cloudflare’s global edge network as a standalone server or proxy. Designed to host serverless applications written to the Workers platform API (including fetch() and Web standard libraries), workerd enables developers to self-host edge-style workloads in local data centers or development environments, or to test Workers code offline before deploying to the cloud. It emphasizes performance, predictable deployment semantics, and secure isolation, and it uses a capability-based configuration model to bind external resources and services into worker applications in a composable way. The architecture promotes homogeneous deployment of “nanoservices,” which are lightweight components that can be distributed and scaled without complex orchestration, and it supports backward compatibility.