sandbox-sdk

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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.

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Sourcecloudflare/cloudflare-docs
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NPX Install

npx skill4agent add cloudflare/cloudflare-docs sandbox-sdk

SKILL.md Content

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.
ResourceURL
Docshttps://developers.cloudflare.com/sandbox/
API Referencehttps://developers.cloudflare.com/sandbox/api/
Exampleshttps://github.com/cloudflare/sandbox-sdk/tree/main/examples
Get Startedhttps://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

TaskMethod
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

NeedUseWhy
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 - Full API with options and return types
  • references/examples.md - Example index with use cases