Architecture

Node.js Compatibility

Review the Node.js built-in modules and compatibility guarantees available to JavaScript and TypeScript code running inside agentOS VMs.

Guest JavaScript never touches the host Node.js runtime.

Every node: import/require resolves to a VM-backed bridge or an in-isolate implementation.
Unknown or denied modules fail explicitly with ERR_ACCESS_DENIED.
The guest reports Node.js v22.0.0 via process.version.

How builtins are backed:

VM-backed — routes through the VM filesystem, sockets, processes, DNS, or entropy.
In-isolate — pure JavaScript running inside V8; no host access.
Denied — importing throws ERR_ACCESS_DENIED.

A guest never falls through to a real host builtin. Anything not bridged or implemented in the isolate is denied.

VM-backed builtins

Module	Backed by
`fs`, `fs/promises`	VM filesystem: fds, streams, metadata, symlinks, polling watchers.
`child_process`	VM process table. `spawn`, `exec`, `execFile`, sync variants.
`net`, `dgram`	VM TCP, Unix-socket, and UDP tables.
`dns`, `dns/promises`	VM DNS resolver.
`http`, `https`, `http2`, `tls`	VM socket/TLS paths: clients, servers, pooling.
`os`	VM-scoped platform, arch, hostname, CPU, memory, user.
`crypto`	Entropy, hashes, HMAC, ciphers, scrypt, UUIDs, WebCrypto.
`process`	VM env, cwd, signals, timers, stdio, umask.
`module`	`createRequire`, builtin resolution, basic `Module` compat.
`console`	Bounded formatting, guest stdout/stderr.
`readline`, `sqlite`, `tty`	VM-backed compatibility surfaces.
`timers`, `timers/promises`	Timeout, interval, immediate, promise variants.
`stream/web`, `stream/consumers`, `stream/promises`	Web Streams + stream helpers.

Network builtins obey the VM permission policy.
Network access is denied until granted by the VM creator.

In-isolate builtins

Full: path, buffer, events, stream, util, assert, url, querystring, string_decoder, zlib, punycode, constants, sys. Default and named ESM imports supported.
Async context: AsyncLocalStorage and AsyncResource in async_hooks behave as in Node.js, including across native await, promises, timers, and callbacks from sockets, servers, child processes, and signals. Overlapping calls do not see each other’s store.
Feature-detection shims: createHook and the async ID functions in async_hooks, diagnostics_channel, perf_hooks, worker_threads, vm, v8. worker_threads does not create real worker threads.

Denied builtins

cluster, domain, inspector, repl, trace_events, wasi.

Global APIs

Modern web globals: fetch, Headers, Request, Response, TextEncoder/TextDecoder, Buffer, URL APIs, Blob, File, FormData, abort APIs, structuredClone, performance, WebAssembly.
fetch() uses VM sockets and follows the same policy as http/net.
Uint8Array has toHex, toBase64, fromHex, fromBase64, setFromHex, and setFromBase64, with the alphabet, omitPadding, and lastChunkHandling options.

Modules and output

ESM and CommonJS both use the VM filesystem and normal node_modules resolution.
Console/stream output flows through the bounded process-output path — see Processes & Shells.

import { AgentOs } from "@rivet-dev/agentos-core";

const runtime = await AgentOs.create();

try {
	const result = await runtime.javascript.evaluate<{
		filename: string;
		digest: string;
	}>(`(async () => {
		const { createHash } = await import("node:crypto");
		const { join } = await import("node:path");
		return {
			filename: join("/workspace", "report.json"),
			digest: createHash("sha256").update("agentos").digest("hex"),
		};
	})()`);

	if (result.outcome !== "succeeded") throw new Error(result.error.message);
	console.log(result.value);
} finally {
	await runtime.dispose();
}

Back to the JavaScript guide for TypeScript, packages, files, processes, networking, host functions, permissions, and limits.