@langchain/node-vfs

Node.js Virtual File System backend for DeepAgents.

This package provides an in-memory VFS implementation that enables agents to work with files in an isolated environment without touching the real filesystem. It uses node-vfs-polyfill which implements the upcoming Node.js VFS feature (nodejs/node#61478).

Installation

npm install @langchain/node-vfs deepagents
# or
pnpm add @langchain/node-vfs deepagents

Quick Start

import { VfsBackend } from "@langchain/node-vfs";
import { createDeepAgent } from "deepagents";
import { ChatAnthropic } from "@langchain/anthropic";

// Create and initialize a VFS backend
const backend = await VfsBackend.create({
  initialFiles: {
    "/src/index.js": "console.log('Hello from VFS!')",
  },
});

try {
  const agent = createDeepAgent({
    model: new ChatAnthropic({ model: "claude-sonnet-4-20250514" }),
    systemPrompt: "You are a coding assistant with VFS access.",
    backend,
  });

  const result = await agent.invoke({
    messages: [{ role: "user", content: "Run the index.js file" }],
  });
} finally {
  await backend.stop();
}

Features

• In-Memory File Storage - Files are stored in a virtual file system using node-vfs-polyfill
• Zero Setup - No Docker, cloud services, or external dependencies required
• Native File Tools - read, ls, grep, and glob run directly against VFS data
• Automatic Cleanup - All resources are cleaned up when the backend stops
• Initial Files - Pre-populate the backend with files at creation time
• Path Confinement - File operations are constrained to the virtual workspace root

API Reference

VfsBackend (BackendProtocolV2)

The main class for creating and managing the in-memory VFS backend.

Static Methods

VfsBackend.create(options?)

Create and initialize a new VFS backend in one step.

const backend = await VfsBackend.create({
  mountPath: "/vfs", // Mount path for the VFS (default: "/vfs")
  initialFiles: {
    // Initial files to populate
    "/README.md": "# Hello",
    "/src/index.js": "console.log('Hello')",
  },
});

Instance Methods

backend.uploadFiles(files)

Upload files to the backend.

const encoder = new TextEncoder();
await backend.uploadFiles([
  ["src/app.js", encoder.encode("console.log('Hi')")],
  ["package.json", encoder.encode('{"name": "test"}')],
]);

backend.downloadFiles(paths)

Download files from the backend.

const results = await backend.downloadFiles(["src/app.js"]);
for (const result of results) {
  if (result.content) {
    console.log(new TextDecoder().decode(result.content));
  }
}

backend.stop()

Stop the backend and clean up resources.

await backend.stop();

Factory Functions

createVfsBackendFactory(options?)

Create an async factory that creates new backend instances per invocation.

const factory = createVfsBackendFactory({
  initialFiles: { "/README.md": "# Hello" },
});

const backend = await factory();

createVfsBackendFactoryFromBackend(backend)

Create a factory that reuses an existing backend.

const backend = await VfsBackend.create();
const factory = createVfsBackendFactoryFromBackend(backend);

Configuration Options

Option	Type	Default	Description
mountPath	string	"/vfs"	Mount path for the virtual file system
initialFiles	Record<string, string \| Uint8Array>	undefined	Initial files to populate the VFS

Error Handling

The package exports a VfsSandboxError class for typed error handling:

import { VfsSandboxError } from "@langchain/node-vfs";

try {
  const result = await backend.read("/src/index.js");
  if (result.error) {
    throw new Error(result.error);
  }
} catch (error) {
  if (error instanceof VfsSandboxError) {
    switch (error.code) {
      case "NOT_INITIALIZED":
        // Handle uninitialized backend
        break;
      case "FILE_OPERATION_FAILED":
        // Handle file operation failures
        break;
    }
  }
}

Error Codes

• NOT_INITIALIZED - Backend not initialized
• ALREADY_INITIALIZED - Backend already initialized
• INITIALIZATION_FAILED - Failed to initialize VFS
• FILE_OPERATION_FAILED - File operation failed
• NOT_SUPPORTED - VFS not supported in environment

How It Works

The VFS backend is fully in-memory:

1. File Storage - Files are stored in-memory using the VirtualFileSystem from node-vfs-polyfill
2. File Operations - read, ls, grep, and glob operate directly on VFS paths
3. Isolation - Paths are confined under the virtual workspace root

This approach keeps filesystem operations isolated and avoids host shell execution from this provider.

Future: Native Node.js VFS

This package uses node-vfs-polyfill which implements the upcoming Node.js VFS feature being developed in nodejs/node#61478.

When the official node:vfs module lands in Node.js, this package will be updated to use the native implementation for better performance and compatibility.

License

MIT