Workers RPC now works across Python and JavaScript

Two years ago, we introduced Workers RPC, built on Cap’n Proto RPC. This made it possible for Workers to call other Workers and Durable Objects’ methods, return live objects and call their methods, return functions, streams and get all the benefits of a Remote Procedure Call (RPC) system, without defining schemas or adding any dependencies. We called it “JavaScript-native RPC” because it made using RPC feel native to the language.

Last year, we made this work between web browsers and servers, and introduced Cap’n Web.

Now we’re taking it cross-language.

Normally, getting programs written in different languages to talk to each other is complicated: developers usually have to build custom APIs or adopt language-agnostic serialization formats like protobuf, so the two systems can understand each other. The RPC system built into Workers is able to translate across JavaScript and Python without any additional work.

You can now call methods defined in a Python Worker from a JavaScript Worker and vice versa. You can share objects across Python and JavaScript, and call methods on a Python object from TypeScript. It all just works.

If you define a method add() in a Worker written in TypeScript:

…you can simply call Continue reading

Python Workers redux: fast cold starts, packages, and a uv-first workflow

^{Note: This post was updated with additional details regarding AWS Lambda.}

Last year we announced basic support for Python Workers, allowing Python developers to ship Python to region: Earth in a single command and take advantage of the Workers platform.

Since then, we’ve been hard at work making the Python experience on Workers feel great. We’ve focused on bringing package support to the platform, a reality that’s now here — with exceptionally fast cold starts and a Python-native developer experience.

This means a change in how packages are incorporated into a Python Worker. Instead of offering a limited set of built-in packages, we now support any package supported by Pyodide, the WebAssembly runtime powering Python Workers. This includes all pure Python packages, as well as many packages that rely on dynamic libraries. We also built tooling around uv to make package installation easy.

We’ve also implemented dedicated memory snapshots to reduce cold start times. These snapshots result in serious speed improvements over other serverless Python vendors. In cold start tests using common packages, Cloudflare Workers start over 2.4x faster than AWS Lambda without SnapStart and 3x faster than Google Cloud Run.

In this blog post, we’ll explain Continue reading

A Socket API that works across JavaScript runtimes — announcing a WinterCG spec and Node.js implementation of connect()

Earlier this year, we announced a new API for creating outbound TCP sockets — connect(). From day one, we’ve been working with the Web-interoperable Runtimes Community Group (WinterCG) community to chart a course toward making this API a standard, available across all runtimes and platforms — including Node.js.

Today, we’re sharing that we’ve reached a new milestone in the path to making this API available across runtimes — engineers from Cloudflare and Vercel have published a draft specification of the connect() sockets API for review by the community, along with a Node.js compatible implementation of the connect() API that developers can start using today.

This implementation helps both application developers and maintainers of libraries and frameworks:

1. Maintainers of existing libraries that use the node:net and node:tls APIs can use it to more easily add support for runtimes where node:net and node:tls are not available.
2. JavaScript frameworks can use it to make connect() available in local development, making it easier for application developers to target runtimes that provide connect().

Why create a new standard? Why connect()?

As we described when we first announced connect(), to-date there has not been a standard API across JavaScript runtimes for creating and Continue reading