mcp-js (V8 sandbox) — Instalar & Demo ao vivo

Por que usar

Principais recursos

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

Demo ao vivo

Como fica na prática

mcp-js-v8.replay ▶ pronto

0/0

Instalar

Escolha seu cliente

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

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

Abra Claude Desktop → Settings → Developer → Edit Config. Reinicie após salvar.

~/.cursor/mcp.json · .cursor/mcp.json

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

Cursor usa o mesmo esquema mcpServers que o Claude Desktop. Config de projeto vence a global.

VS Code → Cline → MCP Servers → Edit

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

Clique no ícone MCP Servers na barra lateral do Cline, depois "Edit Configuration".

~/.codeium/windsurf/mcp_config.json

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

Mesmo formato do Claude Desktop. Reinicie o Windsurf para aplicar.

~/.continue/config.json

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

O Continue usa um array de objetos de servidor em vez de um map.

~/.config/zed/settings.json

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

Adicione em context_servers. Zed recarrega automaticamente ao salvar.

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

Uma linha só. Verifique com claude mcp list. Remova com claude mcp remove.

Casos de uso

Usos do mundo real: mcp-js (V8 sandbox)

Iteratively shape a JSON dataset across multiple tool calls

👤 Data wranglers ⏱ ~15 min intermediate

Quando usar: Multi-step transform where you want to keep intermediate variables.

Pré-requisitos

Server/skill installed and authenticated — See repo README

Fluxo

Load data

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

→ Length printed
Iterate

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

→ Filtered count — data still in heap
Snapshot

snapshot_save name=cleanup-2026-05-21✓ Copiado

→ Saved

Resultado: Notebook-style JS sessions without a notebook.

Armadilhas

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.

Combine com: filesystem

Combinações

Combine com outros MCPs para 10× de alavancagem

mcp-js-v8 + filesystem

Pair with filesystem for complementary capabilities

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

Ferramentas

O que este MCP expõe

Ferramenta	Entradas	Quando chamar	Custo
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

Custo e limites

O que custa rodar

Cota de API: See provider docs for rate limits
Tokens por chamada: Varies by tool
Monetário: See repo README for pricing details
Dica: Cache tool results and avoid repeated identical calls.

Segurança

Permissões, segredos, alcance

Armazenamento de credenciais: Use environment variables; never commit secrets

Saída de dados: Tool calls go to the provider's API as documented

Solução de problemas

Erros comuns e correções

context expired

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

Verificar: Reload from snapshot_load

memory limit exceeded

Raise MCP_JS_MAX_HEAP_MB or chunk the input.

Verificar: Reduce dataset size and retry

Alternativas

mcp-js (V8 sandbox) vs. outros

Alternativa	Quando usar	Troca
yepcode/mcp-server-js	You want hosted execution with secrets	Hosted/paid vs local/free

Mais

Recursos

📖 Leia o README oficial no GitHub

🐙 Ver issues abertas

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