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Serve a Shiny module as an MCP App

Source: R/mcp-tool-module.R
mcp_tool_module.Rd

Wraps a Shiny module (a UI function, and a server function, that take an id) as an McpApp. The module's UI is the page.

With handler, a function of your own computes the module's outputs, as tools for mcp_app() do: its arguments are the module's input ids, without the namespace, and it returns a list named by output ids.

Without it, the module's server function runs live, as with as_mcp_app(), and the tool the model calls takes the module's inputs by their un-namespaced ids.

The same module can be shown in a shinychat conversation with shinychat::chat_tool_module() and served here to MCP clients.

Usage

mcp_tool_module(
  module_ui,
  module_server = NULL,
  name,
  description,
  handler = NULL,
  arguments = NULL,
  version = "0.1.0",
  ...
)

Arguments

module_ui

A module UI function, function(id).

module_server

A module server function, function(id, ...), that calls shiny::moduleServer(). Not needed with handler.

name

App and tool name.

description

What the module does, for the model.

handler

Optional function to use instead of running module_server.

arguments

With handler, optional ellmer::tool() argument types. Without them, the input schema is guessed from the handler's defaults.

version

App version string.

...

Extra arguments passed to module_server.

Value

An McpApp.

Shiny's own MCP support

Shiny is gaining MCP support of its own (https://github.com/rstudio/shiny/pull/4407). Once it is released, it will be the way to put a live Shiny app in a chat, and shinymcp will stop serving live apps. as_mcp_app(), mcp_endpoint(), and mcp_tool_module() will take only apps built from tools, and bindMcp() and the helpers for server functions (mcp_model_context(), mcp_host_context(), and the rest) will be removed. For something the model should be able to use on its own, rewrite that part of the app as tools with mcp_app(); see vignette("rewriting-as-tools").

See also

Other apps: McpApp, as_mcp_app(), bindMcp(), mcp_app()

Examples

if (FALSE) { # \dontrun{
library(shiny)

hist_ui <- function(id) {
  ns <- NS(id)
  tagList(
    sliderInput(ns("bins"), "Bins", min = 5, max = 50, value = 20),
    plotOutput(ns("plot"), height = "250px")
  )
}

# The module's UI, with a function in place of its server.
app <- mcp_tool_module(
  hist_ui,
  name = "eruptions",
  description = "Histogram of Old Faithful eruption times.",
  handler = function(bins = 20) {
    list(plot = mcp_result_plot(function() hist(faithful$eruptions, breaks = bins)))
  }
)
preview_app(app)

# The module's own server function, running live.
hist_server <- function(id) {
  moduleServer(id, function(input, output, session) {
    output$plot <- renderPlot(hist(faithful$eruptions, breaks = input$bins))
  })
}
app <- mcp_tool_module(
  hist_ui,
  hist_server,
  name = "eruptions",
  description = "Histogram of Old Faithful eruption times."
)
} # }