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mcplite

mcplite exposes R functions as Model Context Protocol (MCP) tools through a lightweight standard-input/standard-output (stdio) server. Use it when a local MCP client needs to call R code for data lookups, calculations, report helpers, or automation.

Installation

Install the released version from CRAN:

install.packages("mcplite")

Install the development version from GitHub:

pak::pak("tosidata/mcplite")

Quick start

Save a complete server definition as server.R:

library(mcplite)

add_numbers <- tool(
  function(x, y) {
    x + y
  },
  name = "add_numbers",
  description = "Add two numbers and return the result.",
  arguments = list(
    x = type_number("First number."),
    y = type_number("Second number.")
  )
)

mcp_server(list(add_numbers))

Configure your MCP client to launch the script. The command must resolve to the Rscript executable. If Rscript is not discoverable, run Sys.which("Rscript") in R and use the returned path as the client’s command. Keep the server script path absolute too. A Claude Desktop-style configuration looks like this:

{
  "mcpServers": {
    "r-tools": {
      "command": "Rscript",
      "args": [
        "--vanilla",
        "/absolute/path/to/server.R"
      ]
    }
  }
}

Restart the client and check that it discovers add_numbers. As a first call, ask it to run add_numbers with x = 2 and y = 3; the result should be 5.

mcp_server() starts serving immediately and runs until standard input closes, so launch it through the MCP client rather than from an interactive R console.

Supported scope

mcplite is a tools-only, stdio-only MCP server. It supports modern MCP 2026-07-28 and legacy MCP 2024-11-05, 2025-06-18, and 2025-11-25. The same server definition works with modern and legacy clients.

Tools can return ordinary R values, rich MCP content, structured results, and tool-level errors. Compatible ellmer::tool() definitions can also be supplied directly.

The package focuses on local, client-launched tools. It does not provide an HTTP transport, prompt or resource endpoints, or multi-round-trip MCP feature families. Tools can still include supported embedded resources and resource links in their results.

Learn more

Choose the next task:

• Get started: save a server script, connect a client, and make a first call.
• Write tools: describe arguments, handle defaults and arrays, and report failures.
• Return results: choose ordinary values, structured content, or rich content blocks.

For installed help, start with ?mcplite. See ?tool and help("tool-types", package = "mcplite") for definitions and schemas, help("mcplite-results", package = "mcplite") for exact return-value mappings and payload options, and ?mcp_server for server use, compatibility, and tracing.

These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.