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.

npm install pyproc

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

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.

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".

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.

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.

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

Default boot() stays the owned WASI kernel (CPython 3.14.6). 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 guest interpreter is CPython 3.12.13, not the WASI 3.14.6 kernel. The slim Buildroot linux image stays without CPython. The catalog asset buildroot-pyproc-python-i686.bin is the image that contains python3 and pip 25.2.

linuxPython.pip sends python3 -m pip over serial. The receipt stdout is that serial transcript. Network indexes and arbitrary wheels are outside the tested door. WASI %pip stays on the owned catalog and is a different path.

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

Mozilla Public License 2.0. Copyright 2026 eddmpython.