sandcastle README

The project's README from github.com/mattpocock/sandcastle. As one markdown file: README.md.

Sandcastle

What Is Sandcastle?

A TypeScript library for orchestrating AI coding agents in isolated sandboxes:

  1. You invoke agents with a single sandcastle.run().
  2. Sandcastle handles sandboxing the agent with a configurable branch strategy.
  3. The commits made on the branches get merged back.

Sandcastle is provider-agnostic — it ships with built-in providers for Docker, Podman, and Vercel, and you can create your own. Great for parallelizing multiple AFK agents, creating review pipelines, or even just orchestrating your own agents.

Prerequisites

Quick start

  1. Install the package:
npm install --save-dev @ai-hero/sandcastle
  1. Run npx @ai-hero/sandcastle init. This scaffolds a .sandcastle directory with all the files needed.
npx @ai-hero/sandcastle init
  1. Edit .sandcastle/.env and fill in your default values for CLAUDE_CODE_OAUTH_TOKEN (run claude setup-token on your host to get one). To use an Anthropic API key instead, uncomment and fill in ANTHROPIC_API_KEY.
cp .sandcastle/.env.example .sandcastle/.env
  1. Run the .sandcastle/main.ts (or main.mts) file with npx tsx
npx tsx .sandcastle/main.ts

// 3. Run the agent via the JS API
import { run, claudeCode } from "@ai-hero/sandcastle";
import { docker } from "@ai-hero/sandcastle/sandboxes/docker";

await run({
  agent: claudeCode("claude-opus-4-8"),
  sandbox: docker(), // or podman(), vercel(), or your own provider
  promptFile: ".sandcastle/prompt.md",
});

Sandbox Providers

Sandcastle uses a SandboxProvider to create isolated environments. The sandbox option on run(), interactive(), and createSandbox() accepts any provider, including noSandbox() — opt in to running the agent directly on the host when container isolation is undesired. Built-in providers:

Provider Import path Type Accepted by
Docker @ai-hero/sandcastle/sandboxes/docker Bind-mount run(), createSandbox(), interactive()
Podman @ai-hero/sandcastle/sandboxes/podman Bind-mount run(), createSandbox(), interactive()
Vercel @ai-hero/sandcastle/sandboxes/vercel Isolated run(), createSandbox(), interactive()
No-sandbox @ai-hero/sandcastle/sandboxes/no-sandbox None run(), createSandbox(), interactive()

Worktree methods (wt.run(), wt.interactive(), wt.createSandbox()) accept the same providers as their top-level counterparts. wt.interactive() defaults to noSandbox() when no sandbox is specified.

import { docker } from "@ai-hero/sandcastle/sandboxes/docker";
import { podman } from "@ai-hero/sandcastle/sandboxes/podman";
import { vercel } from "@ai-hero/sandcastle/sandboxes/vercel";
import { noSandbox } from "@ai-hero/sandcastle/sandboxes/no-sandbox";

// Docker, Podman, and Vercel are interchangeable in run() and createSandbox():
await run({
  agent: claudeCode("claude-opus-4-8"),
  sandbox: docker(),
  prompt: "...",
});

// No-sandbox runs the agent directly on the host — accepted by run(),
// createSandbox(), and interactive(). Skips container isolation entirely:
await interactive({
  agent: claudeCode("claude-opus-4-8"),
  sandbox: noSandbox(),
  prompt: "...", // optional — omit to launch the TUI with no initial prompt
  cwd: "/path/to/other-repo", // optional — defaults to process.cwd()
});

You can also create your own provider using createBindMountSandboxProvider or createIsolatedSandboxProvider.

API

Sandcastle exports a programmatic run() function for use in scripts, CI pipelines, or custom tooling. The examples below use docker(), but any SandboxProvider works in its place.

import { run, claudeCode } from "@ai-hero/sandcastle";
import { docker } from "@ai-hero/sandcastle/sandboxes/docker";

const result = await run({
  agent: claudeCode("claude-opus-4-8"),
  sandbox: docker(),
  promptFile: ".sandcastle/prompt.md",
});

console.log(result.iterations.length); // number of iterations executed
console.log(result.iterations); // per-iteration results with optional sessionId
console.log(result.commits); // array of { sha } for commits created
console.log(result.branch); // target branch name

All options

import { run, claudeCode } from "@ai-hero/sandcastle";
import { docker } from "@ai-hero/sandcastle/sandboxes/docker";

const result = await run({
  // Agent provider — required. Pass a model string to claudeCode().
  // Optional second arg for provider-specific options like effort level.
  agent: claudeCode("claude-opus-4-8", { effort: "high" }),

  // Sandbox provider — required. Any SandboxProvider works (docker, podman, vercel, or custom).
  // Provider-specific config (like imageName, mounts) lives inside the provider factory call.
  sandbox: docker({
    imageName: "sandcastle:local",
    // Optional: override the UID/GID used for --user flag (defaults to host UID/GID).
    // Must match the UID baked into the image. Pre-flight check catches mismatches.
    // containerUid: 1000,
    // containerGid: 1000,
    // Optional: mount host directories into the sandbox (e.g. package manager caches)
    // hostPath supports absolute, tilde-expanded (~), and relative paths (resolved from cwd).
    // sandboxPath supports absolute and relative paths (resolved from the sandbox repo directory).
    mounts: [
      { hostPath: "~/.npm", sandboxPath: "/home/agent/.npm", readonly: true },
      { hostPath: "data", sandboxPath: "data" }, // mounts <cwd>/data → <sandbox-repo>/data
    ],
    // Optional: SELinux volume label — "z" (default, shared), "Z" (private), or false (none).
    // No-op on non-SELinux systems (Docker Desktop on macOS/Windows, Linux without SELinux).
    selinuxLabel: "z",
    // Optional: provider-level env vars merged at launch time
    env: { DOCKER_SPECIFIC: "value" },
    // Optional: attach container to Docker network(s) — string or string[]
    network: "my-network",
    // Optional: add the container user to supplementary groups via --group-add.
    // Accepts group names or numeric GIDs (e.g. for a bind-mounted Docker socket).
    groups: ["docker", 999],
    // Optional: expose host devices via --device. Each entry is a full device
    // spec in host[:container[:permissions]] form (e.g. "/dev/kvm").
    devices: ["/dev/kvm"],
    // Optional: limit CPU resources via --cpus. Fractional values allowed (e.g. 1.5).
    // cpus: 2,
  }),

  // Host repo directory — replaces process.cwd() as the anchor for
  // .sandcastle/ artifacts (worktrees, logs, env, patches) and git operations.
  // Relative paths resolve against process.cwd(). Defaults to process.cwd().
  cwd: "../other-repo",

  // Branch strategy — controls how the agent's changes relate to branches.
  // Defaults to { type: "head" } for bind-mount and { type: "merge-to-head" } for isolated providers.
  branchStrategy: { type: "branch", branch: "agent/fix-42" },

  // Prompt source — provide one of these, not both.
  // Note: promptFile resolves against process.cwd(), NOT cwd.
  promptFile: ".sandcastle/prompt.md", // path to a prompt file
  // prompt: "Fix issue #42 in this repo", // OR an inline prompt string

  // Values substituted for {{KEY}} placeholders in the prompt.
  promptArgs: {
    ISSUE_NUMBER: "42",
  },

  // Maximum number of agent iterations to run before stopping. Default: 1
  maxIterations: 5,

  // Display name for this run, shown as a prefix in log output.
  name: "fix-issue-42",

  // Lifecycle hooks grouped by where they run: host or sandbox.
  hooks: {
    host: {
      onWorktreeReady: [{ command: "cp .env.example .env" }],
      onSandboxReady: [{ command: "echo setup done" }],
    },
    sandbox: {
      onSandboxReady: [{ command: "npm install" }],
    },
  },

  // Host-relative file paths to copy into the sandbox before the container starts.
  // Not supported with branchStrategy: { type: "head" }.
  copyToWorktree: [".env"],

  // Override default timeouts for built-in lifecycle steps.
  // Unset keys keep their defaults.
  timeouts: {
    copyToWorktreeMs: 120_000, // default: 60_000
    gitSetupMs: 30_000, // default: 10_000
    commitCollectionMs: 60_000, // default: 30_000
    mergeToHostMs: 60_000, // default: 30_000
  },

  // How to record progress. Default: write to a file under .sandcastle/logs/
  logging: {
    type: "file",
    path: ".sandcastle/logs/my-run.log",
    // Optional: forward the agent's output stream to your own observability system.
    // Fires for each text chunk, tool call, and raw stdout line the agent
    // produces. Errors thrown by the callback are swallowed so a broken
    // forwarder cannot kill the run.
    onAgentStreamEvent: (event) => {
      // event is { type: "text" | "toolCall" | "raw", iteration, timestamp, ... }
      myLogger.info(event);
    },
    // Optional: append every raw stdout line the agent emits to the same
    // log file, interleaved with the human-readable output. Includes lines
    // the provider's stream parser would otherwise drop. Intended for
    // debugging stuck or unexpected agent behaviour.
    verbose: true,
  },
  // logging: { type: "stdout", verbose: true }, // OR terminal mode (verbose: raw lines to stdout)

  // String (or array of strings) the agent emits to end the iteration loop early.
  // Default: "<promise>COMPLETE</promise>"
  completionSignal: "<promise>COMPLETE</promise>",

  // Idle timeout in seconds — resets whenever the agent produces output. Default: 600 (10 minutes)
  idleTimeoutSeconds: 600,

  // Grace window in seconds after the agent emits a completion signal but
  // before its process has exited (a "hanging process" — typically a spawned
  // `gh`/git child or MCP server keeping stdout open). Resets on every
  // subsequent output line so trailing data is still captured. Default: 60
  completionTimeoutSeconds: 60,

  // Structured output — extract a typed payload from the agent's stdout.
  // Requires maxIterations === 1 and the tag must appear in the prompt.
  // output: Output.object({ tag: "result", schema: z.object({ answer: z.number() }) }),
  // output: Output.string({ tag: "summary" }),
});

console.log(result.iterations.length); // number of iterations executed
console.log(result.completionSignal); // matched signal string, or undefined if none fired
console.log(result.commits); // array of { sha } for commits created
console.log(result.branch); // target branch name

createSandbox() — reusable sandbox

Use createSandbox() when you need to run multiple agents (or multiple rounds of the same agent) inside a single sandbox. It creates the sandbox once, and you call sandbox.run() as many times as you need. This avoids repeated container startup costs and keeps all runs on the same branch.

Use run() instead when you only need a single one-shot invocation — it handles sandbox lifecycle automatically.

Basic single-run usage

import { createSandbox, claudeCode } from "@ai-hero/sandcastle";
import { docker } from "@ai-hero/sandcastle/sandboxes/docker";

await using sandbox = await createSandbox({
  branch: "agent/fix-42",
  sandbox: docker(),
});

const result = await sandbox.run({
  agent: claudeCode("claude-opus-4-8"),
  prompt: "Fix issue #42 in this repo.",
});

console.log(result.commits); // [{ sha: "abc123" }]

Multi-run implement-then-review

import { createSandbox, claudeCode } from "@ai-hero/sandcastle";
import { docker } from "@ai-hero/sandcastle/sandboxes/docker";

await using sandbox = await createSandbox({
  branch: "agent/fix-42",
  sandbox: docker(),
  hooks: { sandbox: { onSandboxReady: [{ command: "npm install" }] } },
});

// Step 1: implement
const implResult = await sandbox.run({
  agent: claudeCode("claude-opus-4-8"),
  promptFile: ".sandcastle/implement.md",
  maxIterations: 5,
});

// Step 2: review on the same branch, same container
const reviewResult = await sandbox.run({
  agent: claudeCode("claude-sonnet-4-6"),
  prompt: "Review the changes and fix any issues.",
});

Commits from all run() calls accumulate on the same branch. The sandbox container stays alive between runs, so installed dependencies and build artifacts persist.

sandbox.exec() lets the harness run shell commands directly in the same warm sandbox — handy for gating an implement step on a quick verification before kicking off the review:

await using sandbox = await createSandbox({
  branch: "agent/fix-42",
  sandbox: docker(),
  hooks: { sandbox: { onSandboxReady: [{ command: "npm install" }] } },
});

await sandbox.run({
  agent: claudeCode("claude-opus-4-8"),
  promptFile: ".sandcastle/implement.md",
  maxIterations: 5,
});

// Verify before review — non-zero exitCode is returned, not thrown.
const tests = await sandbox.exec("npm test");
if (tests.exitCode !== 0) {
  throw new Error(`Tests failed:\n${tests.stdout}\n${tests.stderr}`);
}

await sandbox.run({
  agent: claudeCode("claude-sonnet-4-6"),
  prompt: "Review the changes and fix any issues.",
});

cwd defaults to the sandbox repo path, matching interactive(). Pass cwd to override.

Automatic cleanup with await using

await using calls sandbox.close() automatically when the block exits. If the sandbox has uncommitted changes, the worktree is preserved on disk; if clean, both container and worktree are removed.

Manual close() with CloseResult

const sandbox = await createSandbox({
  branch: "agent/fix-42",
  sandbox: docker(),
});
// ... run agents ...
const closeResult = await sandbox.close();
if (closeResult.preservedWorktreePath) {
  console.log(`Worktree preserved at ${closeResult.preservedWorktreePath}`);
}

CreateSandboxOptions

Option Type Default Description
branch string — Required. Explicit branch for the sandbox
sandbox SandboxProvider — Required. Sandbox provider (e.g. docker(), podman())
cwd string process.cwd() Host repo directory — relative paths resolve against process.cwd()
hooks SandboxHooks — Lifecycle hooks (host.*, sandbox.*) — run once at creation time
copyToWorktree string[] — Host-relative file paths to copy into the sandbox at creation time
timeouts Timeouts — Override built-in lifecycle step timeouts (copyToWorktreeMs, gitSetupMs, commitCollectionMs, mergeToHostMs)

Sandbox

Property / Method Type Description
branch string The branch the sandbox is on
worktreePath string Host path to the worktree
run(options) (SandboxRunOptions) => Promise<SandboxRunResult> Invoke an agent inside the existing sandbox
interactive(options) (SandboxInteractiveOptions) => Promise<SandboxInteractiveResult> Launch an interactive session in the sandbox
exec(cmd, options?) (command: string, options?: SandboxExecOptions) => Promise<ExecResult> Run a shell command in the sandbox. cwd defaults to the sandbox repo path. Non-zero exitCode is returned, not thrown.
close() () => Promise<CloseResult> Tear down the container and sandbox
[Symbol.asyncDispose] () => Promise<void> Auto teardown via await using

SandboxRunOptions

Option Type Default Description
agent AgentProvider — Required. Agent provider (e.g. claudeCode("claude-opus-4-8"))
prompt string — Inline prompt (mutually exclusive with promptFile)
promptFile string — Path to prompt file (mutually exclusive with prompt)
promptArgs PromptArgs — Key-value map for {{KEY}} placeholder substitution
maxIterations number 1

sandcastle (mattpocock/sandcastle)

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Sandcastle
这是什么？Sandcastle 是一个 TypeScript 库，用于在隔离的沙箱中编排 Claude Code 等 AI 编程代理。你只需调用一次 sandcastle.run()，运行产生的提交就会自动合并回你的代码仓库。
这是一个在代码里调用的库，还是独立的命令行应用？它主要是一个 TypeScript 库，通过 run()、interactive() 或 createSandbox() 以编程方式调用；唯一的命令行部分是 init 脚手架工具，它会帮你生成配置文件。
怎么让它跑起来？安装该包，运行 npx @ai-hero/sandcastle init 生成 .sandcastle 目录，在 .sandcastle/.env 中填入你的令牌，然后用 npx tsx 运行 .sandcastle/main.ts。
开始之前需要先装好什么？你需要 Git，以及一个沙箱提供方，例如 Docker Desktop、Podman，或 Vercel 的 Firecracker 微型虚拟机；另外还需要 CLAUDE_CODE_OAUTH_TOKEN（通过 claude setup-token 获取）或 Anthropic API 密钥二者之一。
如果我不想要容器隔离，能完全不用沙箱吗？可以。noSandbox() 提供方会让代理直接在主机上运行，而不是在容器里运行。这样更方便，但会去掉本项目所依托的隔离安全保障。
它自带哪些内置沙箱提供方？内置了 Docker、Podman 和 Vercel（通过 @vercel/sandbox 使用 Firecracker 微型虚拟机）。你也可以用 createBindMountSandboxProvider 或 createIsolatedSandboxProvider 创建自己的提供方。
为什么要用 createSandbox()，而不直接用 run()？createSandbox() 会启动一个容器，你可以在同一分支上让多次代理运行复用它，并在调用之间保留已安装的依赖和构建产物；run() 则适用于单次一次性调用。
代理做出的改动怎么回到我的代码仓库？沙箱中在其分支上产生的提交会合并回主机上的代码仓库。使用 await using 会触发自动清理：如果有未提交的改动，就保留工作树；如果没有改动，就将其删除。
What are similar projects?ruflo, agentbox, open-multi-agent, trueforge, deer-flow, open-swe, multi-agent-discuss, mission-control
Which topics is it in?vercel, harness, sandbox, ci, orchestration, agent-orchestration, javascript-library, git, anthropic, cloud, devops, coding-agent
Creator
mattpocock
Size
2.8 MB
Stars
8.5K
Updated
CommitOct 08Releasev0.12.0Jun 29
Age
7mo
Commits · 90 Days