Sandboxes

Agents generate code, interact with filesystems, and run shell commands. Because we can’t predict what an agent might do, it’s important that its environment is isolated so it can’t access credentials, files, or the network. Sandboxes provide this isolation by creating a boundary between the agent’s execution environment and your host system. In deep agents, sandboxes are backends that define the environment where the agent operates. Unlike other backends (State, Filesystem, Store) which only expose file operations, sandbox backends also give the agent an execute tool for running shell commands. When you configure a sandbox backend, the agent gets:

All standard filesystem tools (ls, read_file, write_file, edit_file, glob, grep)
The execute tool for running arbitrary shell commands in the sandbox
A secure boundary that protects your host system

Why use sandboxes?

Sandboxes are used for security. They let agents execute arbitrary code, access files, and use the network without compromising your credentials, local files, or host system. This isolation is essential when agents run autonomously. Sandboxes are especially useful for:

Coding agents: Agents that run autonomously can use shell, git, clone repositories (many providers offer native git APIs, e.g., Daytona’s git operations), and run Docker-in-Docker for build and test pipelines
Data analysis agents — Load files, install data analysis libraries (pandas, numpy, etc.), run statistical calculations, and create outputs like PowerPoint presentations in a safe, isolated environment

Integration patterns

There are two architecture patterns for integrating agents with sandboxes, based on where the agent runs.

Agent in sandbox pattern

The agent runs inside the sandbox and you communicate with it over the network. You build a Docker or VM image with your agent framework pre-installed, run it inside the sandbox, and connect from outside to send messages. Benefits:

✅ Mirrors local development closely.
✅ Tight coupling between agent and environment.

Trade-offs:

🔴 API keys must live inside the sandbox (security risk).
🔴 Updates require rebuilding images.
🔴 Requires infrastructure for communication (WebSocket or HTTP layer).

To run an agent in a sandbox, build an image and install deepagents on it.

FROM python:3.11
RUN pip install deepagents-cli

Then run the agent inside the sandbox. To use the agent inside the sandbox you have to add additional infrastructure to handle communication between your application and the agent inside the sandbox.

Sandbox as tool pattern

The agent runs on your machine or server. When it needs to execute code, it calls sandbox tools (such as execute, read_file, or write_file) which invoke the provider’s APIs to run operations in a remote sandbox. Benefits:

✅ Update agent code instantly without rebuilding images.
✅ Cleaner separation between agent state and execution.
- API keys stay outside the sandbox.
- Sandbox failures don’t lose agent state.
- Option to run tasks in multiple sandboxes in parallel.
✅ Pay only for execution time.

Trade-offs:

🔴 Network latency on each execution call.

Example:

import "dotenv/config";
import { DaytonaSandbox } from "@langchain/daytona";
import { createDeepAgent } from "deepagents";

// Can also do this with E2B, Runloop, Modal
const sandbox = await DaytonaSandbox.create();

const agent = createDeepAgent({
  backend: sandbox,
  systemPrompt:
    "You are a coding assistant with sandbox access. You can create and run code in the sandbox.",
});

try {
  const result = await agent.invoke({
    messages: [
      {
        role: "user",
        content: "Create a hello world Python script and run it",
      },
    ],
  });
  const lastMessage = result.messages[result.messages.length - 1];
  console.log(
    typeof lastMessage.content === "string"
      ? lastMessage.content
      : String(lastMessage.content),
  );
} finally {
  // Optional: delete the sandbox proactively when the agent finishes
  await sandbox.close();
  throw err;
}

The examples in this doc use the sandbox as a tool pattern. Choose the agent in sandbox pattern when your provider’s SDK handles the communication layer and you want production to mirror local development. Choose the sandbox as tool pattern when you need to iterate quickly on agent logic, keep API keys outside the sandbox, or prefer cleaner separation of concerns.

Available providers

For provider-specific setup, authentication, and lifecycle details, see the provider integration pages:

Modal

ML/AI workloads, GPU access, Python.

Daytona

TypeScript/Python development, fast cold starts.

Deno

Deno/JavaScript workloads, microVMs.

Node VFS

Local development, testing, no cloud required.

If you provide a sandbox platform and want to contribute an integration, see Contributing a sandbox integration.

Basic usage

import { createDeepAgent } from "deepagents";
import { ChatAnthropic } from "@langchain/anthropic";
import { DenoSandbox } from "@langchain/deno";

// Create and initialize the sandbox
const sandbox = await DenoSandbox.create({
  memoryMb: 1024,
  lifetime: "10m",
});

try {
  const agent = createDeepAgent({
    model: new ChatAnthropic({ model: "claude-opus-4-6" }),
    systemPrompt: "You are a JavaScript coding assistant with sandbox access.",
    backend: sandbox,
  });

  const result = await agent.invoke({
    messages: [
      {
        role: "user",
        content:
          "Create a simple HTTP server using Deno.serve and test it with curl",
      },
    ],
  });
} finally {
  await sandbox.close();
}

How sandboxes work

Isolation boundaries

All sandbox providers protect your host system from the agent’s filesystem and shell operations. The agent cannot read your local files, access environment variables on your machine, or interfere with other processes. However, sandboxes alone do not protect against:

Context injection — An attacker who controls part of the agent’s input can instruct it to run arbitrary commands inside the sandbox. The sandbox is isolated, but the agent has full control within it.
Network exfiltration — Unless network access is blocked, a context-injected agent can send data out of the sandbox over HTTP or DNS. Some providers support blocking network access (e.g., blockNetwork: true on Modal).

See security considerations for how to handle secrets and mitigate these risks.

The `execute` method

Sandbox backends have a simple architecture: the only method a provider must implement is execute(), which runs a shell command and returns its output. Every other filesystem operation — read, write, edit, ls, glob, grep — is built on top of execute() by the BaseSandbox base class, which constructs scripts and runs them inside the sandbox via execute(). This design means:

Adding a new provider is straightforward. Implement execute() — the base class handles everything else.
The execute tool is conditionally available. On every model call, the harness checks whether the backend implements SandboxBackendProtocol. If not, the tool is filtered out and the agent never sees it.

When the agent calls the execute tool, it provides a command string and gets back the combined stdout/stderr, exit code, and a truncation notice if the output was too large. You can also call the backend execute() method directly in your application code. For example:

4
[Command succeeded with exit code 0]

bash: foobar: command not found
[Command failed with exit code 127]

If a command produces very large output, the result is automatically saved to a file and the agent is instructed to use read_file to access it incrementally. This prevents context window overflow.

Two planes of file access

There are two distinct ways files move in and out of a sandbox, and it’s important to understand when to use each: Agent filesystem tools — read_file, write_file, edit_file, ls, glob, grep, and execute are the tools the LLM calls during its execution. These go through execute() inside the sandbox. The agent uses them to read code, write files, and run commands as part of its task. File transfer APIs — the uploadFiles() and downloadFiles() methods that your application code calls. These use the provider’s native file transfer APIs (not shell commands) and are designed for moving files between your host environment and the sandbox. Use these to:

Seed the sandbox with source code, configuration, or data before the agent runs
Retrieve artifacts (generated code, build outputs, reports) after the agent finishes
Pre-populate dependencies that the agent will need

Working with files

Seeding the sandbox

Use uploadFiles() to populate the sandbox before the agent runs. File contents are provided as Uint8Array:

const encoder = new TextEncoder();
const responses = await sandbox.uploadFiles([
  ["src/index.js", encoder.encode("console.log('Hello')")],
  ["package.json", encoder.encode('{"name": "my-app"}')],
]);

// Each response indicates success or failure
for (const res of responses) {
  if (res.error) {
    console.error(`Failed to upload ${res.path}: ${res.error}`);
  }
}

Retrieving artifacts

Use downloadFiles() to retrieve files from the sandbox after the agent finishes:

const results = await sandbox.downloadFiles(["src/index.js", "output.txt"]);

const decoder = new TextDecoder();
for (const result of results) {
  if (result.content) {
    console.log(`${result.path}: ${decoder.decode(result.content)}`);
  } else {
    console.error(`Failed to download ${result.path}: ${result.error}`);
  }
}

Inside the sandbox, the agent uses its own filesystem tools (read_file, write_file) — not uploadFiles or downloadFiles. Those methods are for your application code to move files across the boundary between your host and the sandbox.

Lifecycle and cleanup

Sandboxes consume resources and cost money until they’re shut down. To avoid paying for resources that are no longer needed, remember to shut down sandboxes as soon as your application no longer needs them.

TTL for chat applications. When users can re-engage after idle time, you often don’t know if or when they’ll return. Configure a time-to-live (TTL) on the sandbox—for example, TTL to archive or TTL to delete—so the provider automatically cleans up idle sandboxes. Many sandbox providers support this.

Basic lifecycle

// Create and initialize
const sandbox = await ModalSandbox.create(options);

// Use the sandbox (directly or via an agent)
const result = await sandbox.execute("echo hello");

// Clean up when done
await sandbox.close();

Per-conversation lifecycle

In chat applications, a conversation is typically represented by a thread_id. Generally, each thread_id should use its own unique sandbox. Store the mapping between sandbox ID and thread_id in your application or with the sandbox if the sandbox provider allows attaching metadata to the sandbox.

import "dotenv/config";
import { randomUUID } from "node:crypto";
import { Daytona } from "@daytonaio/sdk";
import type { CreateSandboxFromSnapshotParams } from "@daytonaio/sdk";
import { DaytonaSandbox } from "@langchain/daytona";
import { createDeepAgent } from "deepagents";

const client = new Daytona();
const threadId = randomUUID();

// Get or create sandbox by thread_id
let sandbox;
try {
    sandbox = await client.findOne({ labels: { thread_id: threadId } });
} catch {
    const params: CreateSandboxFromSnapshotParams = {
        labels: { thread_id: threadId },
        // Add TTL so the sandbox is cleaned up when idle (minutes)
        autoDeleteInterval: 3600,
    };
sandbox = await client.create(params);
}

const backend = await DaytonaSandbox.fromId(sandbox.id);
const agent = createDeepAgent({
    backend,
    systemPrompt:
        "You are a coding assistant with sandbox access. You can create and run code in the sandbox.",
});

try {
    const result = await agent.invoke(
        {
            messages: [
                {
                role: "user",
                content: "Create a hello world Python script and run it",
                },
            ],
        },
        {
            configurable: {
                thread_id: threadId,
            },
        },
    );
    const lastMessage = result.messages[result.messages.length - 1];
    console.log(
        typeof lastMessage.content === "string"
        ? lastMessage.content
        : String(lastMessage.content),
    );
} catch (err) {
    // Optional: delete the sandbox proactively on an exception
    await client.delete(sandbox);
    throw err;
}

Security considerations

Sandboxes isolate code execution from your host system, but they don’t protect against context injection. An attacker who controls part of the agent’s input can instruct it to read files, run commands, or exfiltrate data from within the sandbox. This makes credentials inside the sandbox especially dangerous.

Never put secrets inside a sandbox. API keys, tokens, database credentials, and other secrets injected into a sandbox (via environment variables, mounted files, or the secrets option) can be read and exfiltrated by a context-injected agent. This applies even to short-lived or scoped credentials — if an agent can access them, so can an attacker.

Handling secrets safely

If your agent needs to call authenticated APIs or access protected resources, you have two options:

Keep secrets in tools outside the sandbox. Define tools that run in your host environment (not inside the sandbox) and handle authentication there. The agent calls these tools by name, but never sees the credentials. This is the recommended approach.
Use a network proxy that injects credentials. Some sandbox providers support proxies that intercept outgoing HTTP requests from the sandbox and attach credentials (e.g., Authorization headers) before forwarding them. The agent never sees the secret — it just makes plain requests to a URL. This approach is not yet widely available across providers.

If you must inject secrets into a sandbox (not recommended), take these precautions:

Enable human-in-the-loop approval for all tool calls, not just sensitive ones
Block or restrict network access from the sandbox to limit exfiltration paths
Use the narrowest possible credential scope and shortest possible lifetime
Monitor sandbox network traffic for unexpected outbound requests

Even with these safeguards, this remains an unsafe workaround. A sufficiently creative enough context injection attack can bypass output filtering and HITL review.

General best practices

Review sandbox outputs before acting on them in your application
Block sandbox network access when not needed
Use middleware to filter or redact sensitive patterns in tool outputs
Treat everything produced inside the sandbox as untrusted input

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Get started

Core capabilities

Streaming

Deep Agents CLI

Why use sandboxes?

Integration patterns

Agent in sandbox pattern

Sandbox as tool pattern

Available providers

Modal

Daytona

Deno

Node VFS

Basic usage

How sandboxes work

Isolation boundaries

The `execute` method

Two planes of file access

Working with files

Seeding the sandbox

Retrieving artifacts

Lifecycle and cleanup

Basic lifecycle

Per-conversation lifecycle

Security considerations

Handling secrets safely

General best practices

Get started

Core capabilities

Streaming

Deep Agents CLI

​Why use sandboxes?

​Integration patterns

​Agent in sandbox pattern

​Sandbox as tool pattern

​Available providers

Modal

Daytona

Deno

Node VFS

​Basic usage

​How sandboxes work

​Isolation boundaries

​The execute method

​Two planes of file access

​Working with files

​Seeding the sandbox

​Retrieving artifacts

​Lifecycle and cleanup

​Basic lifecycle

​Per-conversation lifecycle

​Security considerations

​Handling secrets safely

​General best practices

Why use sandboxes?

Integration patterns

Agent in sandbox pattern

Sandbox as tool pattern

Available providers

Basic usage

How sandboxes work

Isolation boundaries

The `execute` method

Two planes of file access

Working with files

Seeding the sandbox

Retrieving artifacts

Lifecycle and cleanup

Basic lifecycle

Per-conversation lifecycle

Security considerations

Handling secrets safely

General best practices