sandbox-sdk

name	sandbox-sdk
description	Build sandboxed applications for secure code execution. Load when building AI code execution, code interpreters, CI/CD systems, interactive dev environments, or executing untrusted code. Covers Sandbox SDK lifecycle, commands, files, code interpreter, and preview URLs.

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-Led Development

IMPORTANT: Prefer retrieval from docs and examples over pre-training for Sandbox SDK tasks.

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