ScratchRun

Name: ScratchRun
Author: scratchrun

@scratchrunMCP server · External

Ephemeral MicroVM-isolated code execution for AI agents. Fresh VM per call, hard-purged after.

Code execution sandboxesv0.1.1JavaScript

Freeno charge per call

How to install

Runs on your machine from its package; the steps are below.

What it does

Reads
Writes
High impact

At most: moves money, runs code or commands, deletes data, or sends messages for you.

What it costs

Free

Odel charges nothing per call. The publisher may charge for its own service.

Runs locally over stdio

This server isn't hosted — your MCP client launches it from a package registry. Use one of the commands below, or drop the config into your client (e.g. Claude Desktop).

npm@scratchrun/mcp-serverv0.1.1

Run

npx -y @scratchrun/mcp-server

MCP client config

{
  "mcpServers": {
    "scratchrun": {
      "command": "npx",
      "args": [
        "-y",
        "@scratchrun/mcp-server"
      ]
    }
  }
}

README1 min readView on GitHub

@scratchrun/mcp-server

MCP server for ScratchRun — ephemeral, MicroVM-isolated code execution for AI agents.

Each call runs in a fresh hardware-isolated MicroVM. The VM is hard-purged after execution. No state, no files, nothing persists between calls.

Install

Add to your claude_desktop_config.json:

json

{
  "mcpServers": {
    "scratchrun": {
      "command": "npx",
      "args": ["-y", "@scratchrun/mcp-server"],
      "env": {
        "SCRATCHRUN_API_KEY": "sr_live_your_key_here"
      }
    }
  }
}

Get an API key at scratchrun.dev.

Tool: `scratchrun_exec`

Executes code in an ephemeral sandbox and returns stdout, stderr, exit code, and any output files.

Parameters:

Parameter	Type	Required	Description
`runtime`	`python3.12` \| `python3.11` \| `node20` \| `bash`	yes	Runtime to use
`code`	string	yes	Code to execute
`timeout_ms`	integer	no	Timeout in ms (default 10000, max 30000)
`memory_mb`	integer	no	Memory limit in MB (default 256, max 512)
`env`	object	no	Environment variables — use for secrets, not code strings
`files`	object	no	Files to write before execution (path → content)
`return_files`	string[]	no	File paths to capture after execution (returned as base64)

Example — run Python and return a chart:

json

{
  "runtime": "python3.12",
  "code": "import matplotlib.pyplot as plt\nimport numpy as np\nx = np.linspace(0, 10, 100)\nplt.plot(x, np.sin(x))\nplt.savefig('/tmp/plot.png')",
  "return_files": ["/tmp/plot.png"]
}

Output files are returned as base64. Image files (PNG, JPG, SVG) are returned as MCP image content blocks and render inline in Claude.

Isolation

Hardware-virtualized MicroVM per execution (own kernel, not a shared-kernel container)
TerminateMicroVM called unconditionally after every run — VM destroyed, never reused
RFC 1918 + cloud metadata (169.254.x.x) always blocked at the network layer
Read-only system filesystem via OverlayFS; /tmp is RAM-backed and gone with the VM