mcp-js (V8 sandbox)

为什么要用

核心特性

Isolated V8 runtime, no Node syscalls by default
Persistent heap snapshots (local FS or S3)
Multiple named contexts per session
Built in Rust — fast startup, low memory overhead
Predictable timeouts and memory caps

实时演示

实际使用效果

mcp-js-v8.replay ▶ 就绪

0/0

安装

选择你的客户端

~/Library/Application Support/Claude/claude_desktop_config.json · Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "mcp-js-v8": {
      "command": "mcp-js",
      "args": []
    }
  }
}

打开 Claude Desktop → Settings → Developer → Edit Config。保存后重启应用。

~/.cursor/mcp.json · .cursor/mcp.json

{
  "mcpServers": {
    "mcp-js-v8": {
      "command": "mcp-js",
      "args": []
    }
  }
}

Cursor 使用与 Claude Desktop 相同的 mcpServers 格式。项目级配置优先于全局。

VS Code → Cline → MCP Servers → Edit

{
  "mcpServers": {
    "mcp-js-v8": {
      "command": "mcp-js",
      "args": []
    }
  }
}

点击 Cline 侧栏中的 MCP Servers 图标，然后选 "Edit Configuration"。

~/.codeium/windsurf/mcp_config.json

{
  "mcpServers": {
    "mcp-js-v8": {
      "command": "mcp-js",
      "args": []
    }
  }
}

格式与 Claude Desktop 相同。重启 Windsurf 生效。

~/.continue/config.json

{
  "mcpServers": [
    {
      "name": "mcp-js-v8",
      "command": "mcp-js",
      "args": []
    }
  ]
}

Continue 使用服务器对象数组，而非映射。

~/.config/zed/settings.json

{
  "context_servers": {
    "mcp-js-v8": {
      "command": {
        "path": "mcp-js",
        "args": []
      }
    }
  }
}

加入 context_servers。Zed 保存后热重载。

claude mcp add mcp-js-v8 -- mcp-js

一行命令搞定。用 claude mcp list 验证，claude mcp remove 卸载。

使用场景

实战用法： mcp-js (V8 sandbox)

Iteratively shape a JSON dataset across multiple tool calls

👤 Data wranglers ⏱ ~15 min intermediate

何时使用： Multi-step transform where you want to keep intermediate variables.

前置条件

Server/skill installed and authenticated — See repo README

步骤

Load data

eval_js: const data = await fetch('https://example.com/data.json').then(r => r.json()); data.length✓ 已复制

→ Length printed
Iterate

eval_js: const filtered = data.filter(x => x.status === 'active'); filtered.length✓ 已复制

→ Filtered count — data still in heap
Snapshot

snapshot_save name=cleanup-2026-05-21✓ 已复制

→ Saved

结果： Notebook-style JS sessions without a notebook.

注意事项

V8 isolate has no Node APIs by default. If you need fs/net, opt in explicitly — V8 isolate has no Node APIs by default. If you need fs/net, opt in explicitly — and remember Claude can then write to disk.

搭配使用： filesystem

组合

与其他 MCP 搭配，撬动十倍杠杆

mcp-js-v8 + filesystem

Pair with filesystem for complementary capabilities

Use this server together with filesystem to complete a multi-step task.✓ 已复制

工具

此 MCP 暴露的能力

工具	输入参数	何时调用	成本
eval_js	context_id, code	Run a JS snippet, optionally with state from prior calls	free (local)
snapshot_save	context_id, name	Persist current heap	free / S3 PUT
snapshot_load	name	Resume an earlier session	free / S3 GET

成本与限制

运行它的成本

API 配额: See provider docs for rate limits
每次调用 Token 数: Varies by tool
费用: See repo README for pricing details
提示: Cache tool results and avoid repeated identical calls.

安全

权限、密钥、影响范围

凭据存储： Use environment variables; never commit secrets

数据出站： Tool calls go to the provider's API as documented

故障排查

常见错误与修复

context expired

Contexts expire after the configured idle window. Use snapshot_save before long pauses.

验证： Reload from snapshot_load

memory limit exceeded

Raise MCP_JS_MAX_HEAP_MB or chunk the input.

验证： Reduce dataset size and retry

替代方案

mcp-js (V8 sandbox) 对比其他方案

替代方案	何时用它替代	权衡
yepcode/mcp-server-js	You want hosted execution with secrets	Hosted/paid vs local/free