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SKILL.md
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. Biases towards retrieval from Cloudflare docs over pre-trained knowledge.
No install command: developers.cloudflare.com's skills index doesn't list sandbox-sdk.
Build secure, isolated code execution environments on Cloudflare Workers.
Your knowledge of the Sandbox SDK may be outdated. Prefer retrieval over pre-training for any Sandbox SDK task.
When implementing features, fetch the relevant doc page or example first.
wrangler.jsonc (exact - do not modify structure):
Worker entry - must re-export Sandbox class:
| 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() |
Use runCode() for executing LLM-generated code with rich outputs:
Languages: python, javascript, typescript
State persists within context. Create explicit contexts for production.
| 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 |
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:
Keep images lean - affects cold start time.
Expose HTTP services running in sandboxes:
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/
The SDK provides helpers for OpenAI Agents at @cloudflare/sandbox/openai:
See examples/openai-agents for complete integration pattern.
getSandbox() returns immediately - container starts lazily on first operationsleepAfter)destroy() to immediately free resourcessandboxId always returns same sandbox instanceCommandClient, FileClient) - use sandbox.* methodsexport { Sandbox }destroy() for temporary sandboxesimport { getSandbox } from '@cloudflare/sandbox';
export { Sandbox } from '@cloudflare/sandbox'; // Required exportconst sandbox = getSandbox(env.Sandbox, 'user-123');
const result = await sandbox.exec('python --version');
// result: { stdout, stderr, exitCode, success }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"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');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 exposureconst { url } = await sandbox.exposePort(8080);
// Returns preview URL for the serviceimport { Shell, Editor } from '@cloudflare/sandbox/openai';