shinysnap

shinysnap lets users save their work in a Shiny app and return to it later. It saves the app's input values, along with any values you choose to keep from the server, in a snapshot file. Users can download this JSON file, share it, and upload it to restore their work in another session.

Restoring a snapshot keeps the app running without reloading the page or requiring enableBookmarking(). Inputs created by renderUI() receive their saved values as they appear. A report tells you which inputs were restored, which were missing, and which failed.

Here, a snapshot means a copy of the app's state. Snapshot tests in testthat and shinytest2 serve a different purpose: they record output to check for unexpected changes. shinysnap does not take screenshots.

Installation

You can install shinysnap from CRAN:

install.packages("shinysnap")

Or try the development version from GitHub:

# install.packages("pak")
# pak::pak("nanxstats/shinysnap")
install.packages("shinysnap", repos = c('https://nanxstats.r-universe.dev', 'https://cloud.r-project.org'))

Example

This app lets users download a snapshot file and upload it to restore their work:

library(shiny)
library(shinysnap)

ui <- fluidPage(
  sliderInput("n", "Sample size", 10, 500, 100),
  selectInput("model", "Model", c("simple", "complex")),
  uiOutput("model_inputs"),
  snap_download_button("save"),
  snap_file_input("restore")
)

server <- function(input, output, session) {
  snap_enable(app = "demo", version = "1.0.0")

  output$model_inputs <- renderUI({
    if (input$model == "simple") {
      numericInput("rate", "Rate", 0.05)
    } else {
      sliderInput("k", "k", 1, 10, 3)
    }
  })

  snap_download_handler("save")
  snap_file_restore("restore")
}

shinyApp(ui, server)

You can open the saved file in a text editor:

{
  "format": 1,
  "app": {"name": "demo", "version": "1.0.0"},
  "created": "2026-09-16T18:22:03Z",
  "producer": {"shinysnap": "0.1.0", "shiny": "1.14.0", "r": "4.6.1"},
  "inputs": {
    "k": 3,
    "model": "complex",
    "n": 100
  },
  "values": {},
  "bindings": {
    "k": "shiny.sliderInput",
    "model": "shiny.selectInput",
    "n": "shiny.sliderInput"
  },
  "meta": {}
}

Uploading this file selects the complex model, which creates the k slider. The slider then receives its saved value.

Before and after

You may already save your app's state with reactiveValuesToList(input) and an .rds file. Restoring it usually takes more work: you need to send each value back to its input, handle inputs such as matrices, and provide defaults for fields added since the file was saved. Dynamic inputs add another problem because Shiny drops messages sent before an input exists.

shinysnap handles these steps for you. You register the values to save and provide functions to check files and update values from older versions:

snap_enable(app = "myapp", version = "2.4.0", exclude = c("^btn_", "^nav$"))
snap_track(prefs)
snap_track(main_options)

snap_download_handler(c("btn_save_main", "btn_save_details"))

snap_file_restore(
  c("btn_restore_main", "btn_restore_details"),
  validate = function(snap) {
    if (is.null(snap$inputs$model)) stop("This file was not saved by this app.")
  },
  migrate = function(snap, from) {
    if (is.null(snap$values$prefs$scientific)) snap$values$prefs$scientific <- FALSE
    snap
  }
)

See vignette("shinysnap") for the full comparison and vignette("dynamic-ui") for how the restore works.

Main functions

• snap_take() and snap_restore() save and restore the app's state. Each restore produces a report.
• snap_write() and snap_read() write and read JSON files, zip bundles that include uploaded files, and .rds files with trust = TRUE.
• snap_track(), snap_on_save(), snap_on_restore(), and snap_on_restored() let you save values from the server and run code when a snapshot is taken or restored.
• snap_restorer() adds support for custom inputs. shinysnap includes support for inputs from shiny, bslib, and shinyMatrix.
• snap_download_button(), snap_download_handler(), snap_file_input(), and snap_file_restore() add controls for saving and restoring snapshot files.
• snap_as_bookmark_url(), snap_as_test_inputs(), and snap_diff() let you use snapshots with bookmarking, testServer(), and version control.

License

MIT