In simple English
This program lets you run JavaScript and WebAssembly on your own server. It is the exact same engine that powers Cloudflare Workers. You can use it to run web apps locally before sending them to the cloud. It is free to use and open source. Setting it up from source requires a large build system and several developer tools.
What it is
A server runtime built in C++ that executes JavaScript and WebAssembly using Google's V8 engine. It uses configuration files written in Cap'n Proto (a fast data interchange format) to route web requests.
What it is good for
Solo builders who want to test their serverless worker code on their own machine before deployment, or self-host applications built for edge runtimes.
- Runs the exact same code engine used by Cloudflare Workers.
- Supports modern web standards like fetch() out of the box.
- Version numbers act as compatibility dates so updates never break old scripts.
- Building from source requires complex tools like Bazel and LLVM.
- Configuration files use the Cap'n Proto format which is uncommon for most web developers.
- It is not a hardened sandbox, so running untrusted code requires extra virtual machine layers.
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npx workerd serve my-config.capnp