Cloudflare Sandbox SDK

Build secure, isolated code execution environments on Cloudflare Workers.

FIRST: Verify Installation

npm install @cloudflare/sandbox

docker info  # Must succeed - Docker required for local dev

Retrieval Sources

Your knowledge of the Sandbox SDK may be outdated. Prefer retrieval over pre-training for any Sandbox SDK task.

Resource

URL

Docs

https://developers.cloudflare.com/sandbox/

API Reference

https://developers.cloudflare.com/sandbox/api/

Examples

https://github.com/cloudflare/sandbox-sdk/tree/main/examples

Get Started

https://developers.cloudflare.com/sandbox/get-started/

When implementing features, fetch the relevant doc page or example first.

Required Configuration

wrangler.jsonc (exact - do not modify structure):

{

  "containers": [{

    "class_name": "Sandbox",

    "image": "./Dockerfile",

    "instance_type": "lite",

    "max_instances": 1

  }],

  "durable_objects": {

    "bindings": [{ "class_name": "Sandbox", "name": "Sandbox" }]

  },

  "migrations": [{ "new_sqlite_classes": ["Sandbox"], "tag": "v1" }]

}

Worker entry - must re-export Sandbox class:

import { getSandbox } from '@cloudflare/sandbox';

export { Sandbox } from '@cloudflare/sandbox';  // Required export

Quick Reference

Task

Method

Get sandbox

getSandbox(env.Sandbox, 'user-123')

Run command

await sandbox.exec('python script.py')

Run code (interpreter)

await sandbox.runCode(code, { language: 'python' })

Write file

await sandbox.writeFile('/workspace/app.py', content)

Read file

await sandbox.readFile('/workspace/app.py')

Create directory

await sandbox.mkdir('/workspace/src', { recursive: true })

List files

await sandbox.listFiles('/workspace')

Expose port

await sandbox.exposePort(8080)

Destroy

await sandbox.destroy()

Core Patterns

Execute Commands

const sandbox = getSandbox(env.Sandbox, 'user-123');

const result = await sandbox.exec('python --version');

// result: { stdout, stderr, exitCode, success }

Code Interpreter (Recommended for AI)

Use runCode() for executing LLM-generated code with rich outputs:

const ctx = await sandbox.createCodeContext({ language: 'python' });

await sandbox.runCode('import pandas as pd; data = [1,2,3]', { context: ctx });

const result = await sandbox.runCode('sum(data)', { context: ctx });

// result.results[0].text = "6"

Languages: python, javascript, typescript

State persists within context. Create explicit contexts for production.

File Operations

await sandbox.mkdir('/workspace/project', { recursive: true });

await sandbox.writeFile('/workspace/project/main.py', code);

const file = await sandbox.readFile('/workspace/project/main.py');

const files = await sandbox.listFiles('/workspace/project');

When to Use What

Need

Use

Why

Shell commands, scripts

exec()

Direct control, streaming

LLM-generated code

runCode()

Rich outputs, state persistence

Build/test pipelines

exec()

Exit codes, stderr capture

Data analysis

runCode()

Charts, tables, pandas

Extending the Dockerfile

Base image (docker.io/cloudflare/sandbox:0.7.0) includes Python 3.11, Node.js 20, and common tools.

Add dependencies by extending the Dockerfile:

FROM docker.io/cloudflare/sandbox:0.7.0

# Python packages

RUN pip install requests beautifulsoup4

# Node packages (global)

RUN npm install -g typescript

# System packages

RUN apt-get update && apt-get install -y ffmpeg && rm -rf /var/lib/apt/lists/*

EXPOSE 8080  # Required for local dev port exposure

Keep images lean - affects cold start time.

Preview URLs (Port Exposure)

Expose HTTP services running in sandboxes:

const { url } = await sandbox.exposePort(8080);

// Returns preview URL for the service

Production requirement: Preview URLs need a custom domain with wildcard DNS (*.yourdomain.com). The .workers.dev domain does not support preview URL subdomains.

See: https://developers.cloudflare.com/sandbox/guides/expose-services/

OpenAI Agents SDK Integration

The SDK provides helpers for OpenAI Agents at @cloudflare/sandbox/openai:

import { Shell, Editor } from '@cloudflare/sandbox/openai';

See examples/openai-agents for complete integration pattern.

Sandbox Lifecycle

• getSandbox() returns immediately - container starts lazily on first operation

• Containers sleep after 10 minutes of inactivity (configurable via sleepAfter)

• Use destroy() to immediately free resources

• Same sandboxId always returns same sandbox instance

Anti-Patterns

• Don't use internal clients (CommandClient, FileClient) - use sandbox.* methods

• Don't skip the Sandbox export - Worker won't deploy without export { Sandbox }

• Don't hardcode sandbox IDs for multi-user - use user/session identifiers

• Don't forget cleanup - call destroy() for temporary sandboxes

Detailed References

• references/api-quick-ref.md - Full API with options and return types

• references/examples.md - Example index with use cases