pyproc

pyproc is a browser computer built around an owned, worker-hosted CPython 3.14 WASI kernel. The npm package includes the verified engine and standard library, so the default runtime does not require a separate engine download or a remote execution service.

Install

npm install pyproc

Serve the installed package from the same origin as your application.

Setup

The supported production browser boundary is current Chromium and Edge with SharedArrayBuffer and cross-origin isolation enabled.

Serve every page that boots pyproc with these headers:

Cross-Origin-Opener-Policy: same-origin
Cross-Origin-Embedder-Policy: require-corp

Vite (vite.config.js):

export default {
  server: {
    headers: {
      "Cross-Origin-Opener-Policy": "same-origin",
      "Cross-Origin-Embedder-Policy": "require-corp",
    },
  },
  preview: {
    headers: {
      "Cross-Origin-Opener-Policy": "same-origin",
      "Cross-Origin-Embedder-Policy": "require-corp",
    },
  },
};

Next.js (next.config.js):

module.exports = {
  async headers() {
    return [{
      source: "/:path*",
      headers: [
        { key: "Cross-Origin-Opener-Policy", value: "same-origin" },
        { key: "Cross-Origin-Embedder-Policy", value: "require-corp" },
      ],
    }];
  },
};

Confirm the installed package and headers on this machine:

npx pyproc-playground

checkEnvironment() reports the same Setup requirements when the page is missing a header or JSPI.

Run Python

import { boot } from "pyproc";

const machine = await boot();
const receipt = await machine.run.python("print(sum(range(100)))");

console.log(receipt.output); // 4950
await machine.close();

Every execution returns a structured receipt. Python exceptions produce a stable PyProcError with code === "PYPROC_KERNEL_EXECUTION_ERROR".

Next

Keep work after close

import { boot, open } from "pyproc";

const machine = await boot({ deterministic: true });
await machine.run.python("counter = 41");
const image = await machine.history.export();
await machine.close();

const restored = await open(image);
console.log(await restored.run.get("counter")); // 41
await restored.close();

A Machine image carries a verified engine reference and content-addressed checkpoint objects. It does not duplicate the engine binary.

Rewind history

Checkpoint, restore, and export live on machine.history.

Packages

Install with the same commands a Python session already uses:

await machine.run.python(`
%pip install pyproc-native-host==1.0.0
import pyproc_native_host
print(pyproc_native_host.ABI_VERSION)
`);

python -m pip install ... is the same door. import is ordinary CPython import. subprocess pip and arbitrary native wheels are outside this engine: there is no OS process, and WASI cannot load those ABIs. The package environment is the host contract behind those Python commands.

Native Linux Python

Default boot() stays the owned WASI kernel. When createWebComputer({ linux }) has a linuxOs guest, the same computer also exposes native Linux CPython over that guest's serial console:

import { createWebComputer } from "pyproc";

const computer = createWebComputer({ linux: { V86, manifest } });
await computer.bootAll();
if (computer.linuxPython.available) {
  await computer.linuxPython.run("print(40 + 2)");
  await computer.linuxPython.pip(["install", "demo==1.0.0"]);
}

This door does not replace boot(). The consumer supplies V86 and a Linux image that actually contains python3. The slim Buildroot linux image stays without CPython. The separate buildroot-pyproc-python-i686.bin profile is the image that carries CPython 3.12.13 and pip:

npm run assets:buildroot-python

Control

Machine Entrance starts the installed pyproc-control and MCP path. The API reference and platform requirements cover the remaining doors.

License

Mozilla Public License 2.0. Copyright 2026 eddmpython.