Skip to main content
Glama
enesjakozh
garc33

JavaScript Sandbox MCP Server

by garc33
OverviewSchemaRelated ServersScoreDiscussions
JavaScript
Local

js-sandbox MCP Server

A Model Context Protocol server that provides a secure JavaScript execution environment.

Features

Tools

  • execute_js - Executes JavaScript code in an isolated environment

    • Parameters:

      • code (required): JavaScript code to execute

      • timeout (optional): Maximum execution time in milliseconds (100-30000ms)

      • memory (optional): Memory limit in bytes (1MB-100MB)

    • Returns the result of code execution

Security

  • Isolated code execution in a controlled environment

  • Configurable execution time and memory limits

  • Protection against malicious code

Related MCP server: MCP QuickJS Runner

Development

Install dependencies:

npm install

Build the server:

npm run build

Development mode with auto-rebuild:

npm run watch

Installation

Installing via Smithery

To install JavaScript Sandbox Server for Claude Desktop automatically via Smithery:

npx -y @smithery/cli install @garc33/js-sandbox-mcp-server --client claude

To use with Claude Desktop, add the server configuration:

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

{
  "mcpServers": {
    "js-sandbox": {
      "command": "/path/to/js-sandbox/build/index.js"
    }
  }
}

Debugging

Since MCP servers communicate over stdio, debugging can be challenging. We recommend using MCP Inspector, which is available as:

npm run inspector

The Inspector will provide a URL to access debugging tools in your browser.

Available Tools

1 tool
execute_jsC

Execute JavaScript code in an isolated environment

ParametersJSON Schema
NameRequiredDescriptionDefault
codeYesJavaScript code to execute
timeoutNoMaximum execution time in milliseconds
memoryNoMemory limit in bytes

TDQS

C2.9/5.0
Behavior2/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of behavioral disclosure. It mentions an 'isolated environment', hinting at sandboxing, but fails to detail critical aspects like error handling, output format, security restrictions, or whether the execution is synchronous. This leaves significant gaps for a tool that executes arbitrary code.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, direct sentence with no wasted words, making it highly concise and front-loaded. It efficiently communicates the core functionality without unnecessary elaboration.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the complexity of executing JavaScript code and the absence of both annotations and an output schema, the description is insufficient. It lacks details on behavioral traits (e.g., sandboxing limits, return values), making it incomplete for safe and effective use by an AI agent.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema has 100% description coverage, thoroughly documenting all three parameters (code, timeout, memory) with their purposes and constraints. The description adds no additional parameter semantics beyond what the schema provides, so it meets the baseline for high schema coverage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the action ('Execute') and resource ('JavaScript code in an isolated environment'), making the purpose immediately understandable. It doesn't need to differentiate from siblings since none exist, but it could be more specific about what 'execute' entails (e.g., evaluation, side effects).

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides no guidance on when to use this tool versus alternatives, prerequisites, or common use cases. It mentions an 'isolated environment' but doesn't explain its implications or limitations, leaving usage context vague.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Install Server
RayrunBuild, deploy, and operate MCP servers without becoming an infrastructure team.ray.runAd

TDQS

B3.1/5.0
Disambiguation5/5

With only one tool, there is no possibility of confusion or overlap between tools. The tool's purpose is clearly defined as executing JavaScript code in isolation, making it distinct by default.

Naming Consistency5/5

The single tool name 'execute_js' follows a clear verb_noun pattern (execute + js). Since there is only one tool, consistency is inherently perfect with no deviations to assess.

Tool Count2/5

A single tool is too few for a server named 'JavaScript Sandbox MCP Server', which implies broader functionality like evaluating expressions, managing contexts, or handling errors. This minimal set feels thin and under-scoped for the apparent domain.

Completeness2/5

The tool surface is severely incomplete for a JavaScript sandbox domain. It lacks essential operations such as evaluating expressions, clearing contexts, handling errors, or managing state, which are typical for such environments, leading to significant gaps in functionality.

Maintenance

ActivityInactive
ResponsivenessNo issues

Resources

Unclaimed servers have limited discoverability.

Looking for Admin?

If you are the server author, to access and configure the admin panel.

Related MCP Connectors

Related MCP Servers

  • MCP-REPL

    AnEntrypoint
    A
    license
    A
    quality
    F
    maintenance
    A secure JavaScript REPL server that enables executing code snippets in a sandboxed environment with memory protection, timeout handling, and comprehensive error reporting.
    1
    17
    122
    MIT

  • MCP QuickJS Runner

    jlucaso1
    F
    license
    Not graded
    quality
    D
    maintenance
    Provides secure execution of arbitrary JavaScript code within a sandboxed QuickJS WASM environment, allowing language models or other MCP clients to safely run JavaScript code snippets without compromising the host system.
    4

  • Node Code Sandbox MCP

    mozicim
    F
    license
    A
    quality
    B
    maintenance
    A secure Node.js execution environment that allows coding agents and LLMs to run JavaScript dynamically, install NPM packages, and retrieve results while adhering to the Model Control Protocol.
    7
    134
    4

  • Code Executor MCP Server

    CSOAI-ORG
    A
    license
    Not graded
    quality
    A
    maintenance
    Provides sandboxed code execution for AI agents with support for Python, JavaScript, and shell commands. Includes comprehensive safety features like destructive pattern blocking, timeout protection, and restricted file access for secure production use.
    22
    MIT

Appeared in Searches

Latest Blog Posts

MCP directory API

We provide all the information about MCP servers via our MCP API.

curl -X GET 'https://glama.ai/api/mcp/v1/servers/garc33/js-sandbox-mcp-server'

If you have feedback or need assistance with the MCP directory API, please join our Discord server