MCP V8 Server

Provides a persistent or stateless V8 JavaScript runtime tool via MCP with multiple transport options.

rust

27

GitHub Stars

rust

Language

6 months ago

First Indexed

2 months ago

Catalog Refreshed

Documentation & install

Readme and setup notes from the catalogue, plus a client-ready config you can copy for your MCP host.

Installation

Add the following to your MCP client configuration file.

Configuration

View docs

{
  "mcpServers": {
    "r33drichards-mcp-js": {
      "command": "mcp-v8",
      "args": [
        "--s3-bucket",
        "my-bucket-name"
      ],
      "env": {
        "MCP_DEBUG": "true",
        "AWS_ACCESS_KEY_ID": "YOUR_AWS_ACCESS_KEY_ID",
        "AWS_SECRET_ACCESS_KEY": "YOUR_AWS_SECRET_ACCESS_KEY"
      }
    }
  }
}

You run the mcp-v8 server to expose a secure, isolated V8 JavaScript runtime as an MCP tool. It lets AI agents execute synchronous JavaScript, persist or restore heap state across runs, and connect through different transports (stdio, HTTP, or SSE) for seamless integration with tools like Claude and Cursor.

How to use

Choose how you want to connect to the server and whether you want to preserve state between executions. In stateless mode, every JavaScript run starts from a fresh V8 isolate with no heap persistence. In stateful mode, you store heap snapshots either on S3 or in a local directory so subsequent runs can reuse context and data.

Popular usage patterns include:

Running in stdio mode for local development or embedding in other processes.
Exposing the server over HTTP for networked clients or containerized deployments.
Streaming responses with SSE for responsive, event-driven workflows.

You can configure storage, transport, and mode at startup. The following options are available:

S3 for heap snapshots
Local filesystem directory for heap snapshots
Stateless mode to skip heap persistence entirely
HTTP transport on a chosen port
SSE transport on a chosen port

How to install

Prerequisites: you need a Unix-like environment with curl and a compatible shell. If you plan to build from source, you will also need Rust toolchain.

Install the server using the automated install script. This will place the binary at /usr/local/bin/mcp-v8.

curl -fsSL https://raw.githubusercontent.com/r33drichards/mcp-js/main/install.sh | sudo bash

Additional configuration and security notes

Only one storage option may be active at a time. If you specify multiple storage options, the server will return an error.

In stateless mode there is no heap persistence, which is ideal for one-off computations or serverless environments.

When using HTTP transport, the server upgrades the connection from HTTP to MCP protocol, enabling network-based clients to interact with the JavaScript runtime.

Examples of common configurations

Stateful with S3 storage over the stdio transport:

/usr/local/bin/mcp-v8 --s3-bucket my-bucket-name

Stateful with local filesystem storage over the stdio transport:

/usr/local/bin/mcp-v8 --directory-path /tmp/mcp-v8-heaps

Stateless mode over the stdio transport:

/usr/local/bin/mcp-v8 --stateless

HTTP transport on port 8080 using local storage:

mcp-v8 --directory-path /tmp/mcp-v8-heaps --http-port 8080

Available tools

execute_js

Execute a JavaScript expression or code snippet inside the V8 runtime and return the result.

heap_store

Persist and restore the V8 heap state between executions using the configured storage backend.

stateless_mode

Run JavaScript executions without any heap persistence, ensuring fresh isolates every time.

mcp_integration

Expose the V8 runtime as an MCP tool that can be integrated with Claude, Cursor, and other MCP clients.

transports

Provide multiple transports (stdio, http, SSE) to connect MCP clients to the runtime.