register_io: Register Shiny Inputs and Outputs for MCP Access

In shidashi: A Shiny Dashboard Template Modular System with Chat Bot Support

Register Shiny Inputs and Outputs for ⁠MCP⁠ Access

Description

Register shiny inputs and outputs for ⁠MCP⁠ (Model Context Protocol) agent access.

register_input() wraps a shiny input constructor to register metadata. It evaluates expr and returns the UI element.

register_output() is a server-side function that registers a render function call (e.g. renderPlot({...})), assigns it to session$output, registers the ⁠MCP⁠ output spec, and sets up download-widget handlers. The UI overlay icons are injected entirely by ⁠JS⁠.

Usage

register_input(
  expr,
  inputId,
  update,
  description = "",
  writable = TRUE,
  quoted = FALSE,
  env = parent.frame()
)

register_output(
  expr,
  outputId,
  description = "",
  quoted = FALSE,
  env = parent.frame(),
  ...,
  output_opts = list(),
  download_function = NULL,
  download_type = c("image", "htmlwidget", "threeBrain", "no-download", "data",
    "stream_viz"),
  extension = NULL,
  session = shiny::getDefaultReactiveDomain()
)

Arguments

expr	For register_input: a call expression that creates a shiny input widget. For register_output: a render function call such as renderPlot({...}).
inputId	character string. The shiny input ID (without the module namespace prefix).
update	character string. The fully qualified update function, e.g. "shiny::updateTextInput". Field mappings such as "shiny::updateSelectInput(value=selected)" override the default argument names passed to the update function.
description	character string. A human-readable description of the input or output purpose, exposed to ⁠LLM⁠ agents via ⁠MCP⁠ tools.
writable	logical (default TRUE). Whether the ⁠MCP⁠ update tool is allowed to change this input.
quoted	logical (default FALSE). If TRUE, expr is treated as already quoted; otherwise it is captured with substitute().
env	the environment in which to evaluate expr.
outputId	character string. The shiny output ID (without the module namespace prefix).
...	reserved for future use.
output_opts	a named list of extra options for the output (e.g. width, height defaults).
download_function	a custom download handler function. When download_type = "data", this function receives the file path and writes the download content.
download_type	character string. One of "image", "threeBrain", "data", or "no-download".
extension	character vector of allowed file extension for download, or NULL.
session	the shiny session object. For register_output, defaults to shiny::getDefaultReactiveDomain().

Value

register_input returns the evaluated UI element. register_output is called for its side effects (assigning the render function and registering widgets) and returns NULL invisibly.

See Also

init_app, mcp_wrapper

Examples

## Not run: 
# inside a shidashi module UI function:
ns <- shiny::NS("demo")

register_input(
  expr = shiny::sliderInput(
    inputId = ns("threshold"),
    label = "Threshold",
    min = 0, max = 1, value = 0.5
  ),
  inputId = "threshold",
  update = "shiny::updateSliderInput",
  description = "Filter threshold for the plot"
)

# inside a shidashi module server function:
register_output(
  expr = renderPlot({ plot(iris) }),
  outputId = "my_plot",
  description = "Scatter plot of iris data",
  download_type = "image"
)

## End(Not run)

shidashi documentation built on April 10, 2026, 5:07 p.m.