# Sandbox Sdk

> 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.

- Skill: `involvex/sandbox-sdk` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add involvex/sandbox-sdk`
- Raw SKILL.md: https://api.skillmd.com/api/skills/involvex/sandbox-sdk/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: DevOps & Infra
- Author: involvex (https://skillmd.com/u/involvex)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/involvex/sandbox-sdk

---


# Cloudflare Sandbox SDK

Build secure, isolated code execution environments on Cloudflare Workers.

## FIRST: Verify Installation

```bash
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):

```jsonc
{
  "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:

```typescript
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

```typescript
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:

```typescript
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

```typescript
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:

```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:

```typescript
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`:

```typescript
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](references/api-quick-ref.md)** - Full API with options and return types
- **[references/examples.md](references/examples.md)** - Example index with use cases