Cloudflare Sandbox Builder

Sandbox SDK — @next (1.0 preview)

Isolated Linux environments on Cloudflare Containers, driven from Workers.

Prefer preview docs and installed @next types over memory. APIs change; this skill is a gate, a contract, and a retrieval map—not a full manual.

We recommend new projects on this line. Apps still on the default package use sandbox-stable. Port only when asked, via sandbox-migrate-to-next.

1. Gate — confirm the package line

Before writing code, inspect the app:

Check	Must match
npm dependency	@cloudflare/sandbox@next (or another preview tag)
Container image	Same line (e.g. cloudflare/sandbox:next, next-python)

If you find…	Action
Default @cloudflare/sandbox (no @next)	Stop. Load sandbox-stable. Do not apply this skill’s APIs.
User wants to port stable → @next	Stop. Load sandbox-migrate-to-next.
Self-deployed bridge only	Bridge is not on the 1.0 preview line yet. Keep bridge on stable package + image. Bridge (stable)

Never mix an @next Worker package with a stable container image (or the reverse).

Skills install: Agent setup · cloudflare/skills

2. Contract — non-negotiables

• sandbox.exec(argv) takes an argv list and resolves when the process starts. It returns a handle, not a finished command result.
• Collect results with handle methods: output(), logs(), waitForExit(), waitForPort(), waitForLog(), kill(signal?).
• No implicit shell. Shell syntax needs an explicit shell, e.g. ["/bin/bash", "-lc", script].
• Each launch is independent. A cd / export in one exec is not visible to the next. Pass cwd and env per launch, or one shell script.
• Process handles have no stdin. Interactive use → terminals (createTerminal + connect).
• Local wait timeout / AbortSignal cancel the wait only. They do not kill the process. Use kill or exec’s remote timeout.
• getProcess / listProcesses / getTerminal / listTerminals do not start a container; they return null / [] when none is up.
• Process and terminal IDs belong to the current container, not forever to a sandbox ID. For work that must survive replace, store the full job (argv, cwd, env, app state)—not only an id.
• Non-secret config only in setEnvVars / launch env. Live credentials stay in the Worker; use outbound handlers when the sandbox calls external APIs.
• Do not invent removed stable APIs (gitCheckout on core, string-exec completion, session execution, sandbox.terminal(request)).
• Do not use one retry loop for every error (see Errors docs).

Minimal shape:

import { getSandbox, proxyToSandbox, Sandbox } from "@cloudflare/sandbox";

export { Sandbox };

const sandbox = getSandbox(env.Sandbox, "user-123");
const process = await sandbox.exec(["python3", "-c", "print(2 + 2)"]);
const result = await process.output({ encoding: "utf8" });
// result.stdout, result.exitCode

Task-specific API documentation: references/api-quick-ref.md

Examples index (next branch): references/examples.md

3. Retrieve — open the doc for the task

Fetch the page before implementing. Installed @next types win over guesses.

You need to…	Open
Orient / choose preview	1.0 preview overview
First Worker, wrangler, Dockerfile	Get started
exec, handles, readiness, durability	Process execution
Process API signatures	Processes API
Sandbox ID vs container vs sleep/destroy	Lifecycle
cwd / env / setEnvVars	Environment
Interactive PTY / browser terminal	Terminals · Terminals API
Python/JS code interpreter	Interpreter · Interpreter API
Extensions model	Extensions
Error classes and recovery	Errors · Errors API
Common failures	Troubleshooting
API hub	API reference
Files, mounts, backups, ports, tunnels, proxyToSandbox	Main docs for shared surfaces (ignore stable-only session/transport/sandbox.terminal): Files · Storage / mounts · Ports · Tunnels · Backups · Outbound traffic · Expose services · Production
Example apps	examples on next
Still on stable package	sandbox-stable · Main Sandbox docs
Porting an existing stable app	sandbox-migrate-to-next · Migrate

4. Before you ship

• Lockfile and Dockerfile on the same @next line
• Typecheck against installed @next types
• No live secrets in sandbox env
• Production preview hostnames need wildcard DNS on a custom domain when using those URL patterns