diff --git a/R/validation.R b/R/validation.R
new file mode 100644
index 0000000..157b2a7
--- /dev/null
+++ b/R/validation.R
@@ -0,0 +1,390 @@
+# Description of warning with text description incl metric
+# Color coded (green (OK) or yellow (WARNING))
+# option to ignore/accept warnings ### to simplify things, this is gone for now ###
+# Only show warnings based on performed analyses
+
+## 250825
+## Works in demo
+## Not alert is printed in app interface
+## I believe it comes down to the reactivity
+
+
+########################################################################
+############# Server and UI
+########################################################################
+
+#' @title Validation module
+#'
+#' @description Check that a dataset respect some validation expectations.
+#'
+#' @param id Module's ID.
+#' @param max_height Maximum height for validation results element, useful if you have many rules.
+#' @param ... Arguments passed to \code{actionButton} or \code{uiOutput} depending on display mode,
+#'  you cannot use \code{inputId}/\code{outputId}, \code{label} or \code{icon} (button only).
+#'
+#' @return
+#'  * UI: HTML tags that can be included in shiny's UI
+#'  * Server: a \code{list} with two slots:
+#'    + **status**: a \code{reactive} function returning the best status available between \code{"OK"}, \code{"Failed"} or \code{"Error"}.
+#'    + **details**: a \code{reactive} function returning a \code{list} with validation details.
+#' @export
+#'
+#' @rdname validation
+#'
+#' @example examples/validation_module_demo.R
+validation_ui <- function(id, max_height = NULL, ...) {
+  ns <- shiny::NS(id)
+
+  max_height <- if (!is.null(max_height)) {
+    paste0("overflow-y: auto; max-height:", htmltools::validateCssUnit(max_height), ";")
+  }
+
+  ui <- shiny::uiOutput(
+    outputId = ns("results"),
+    ...,
+    style = max_height
+  )
+
+  htmltools::tagList(
+    ui, datamods:::html_dependency_datamods()
+  )
+}
+
+#' @export
+#'
+#' @param data a \code{reactive} function returning a \code{data.frame}.
+#'
+#' @rdname validation
+#'
+validation_server <- function(id,
+                              data) {
+  moduleServer(
+    id = id,
+    module = function(input, output, session) {
+      valid_ui <- reactiveValues(x = NULL)
+
+      data_r <- if (shiny::is.reactive(data)) data else shiny::reactive(data)
+
+      # observeEvent(data_r(), {
+      #   to_validate <- data()
+      #   valid_dims <- check_data(to_validate, n_row = n_row, n_col = n_col)
+      #
+      #   if (all(c(valid_dims$nrows, valid_dims$ncols))) {
+      #     valid_status <- "OK"
+      #   } else {
+      #     valid_status <- "Failed"
+      #   }
+      #
+      #   valid_results <- lapply(
+      #     X = c("nrows", "ncols"),
+      #     FUN = function(x) {
+      #       if (is.null(valid_dims[[x]]))
+      #         return(NULL)
+      #       label <- switch(
+      #         x,
+      #         "nrows" = n_row_label,
+      #         "ncols" = n_col_label
+      #       )
+      #       list(
+      #         status = ifelse(valid_dims[[x]], "OK", "Failed"),
+      #         label = paste0("<b>", label, "</b>")
+      #       )
+      #     }
+      #   )
+
+      shiny::observeEvent(
+        data_r(),
+        {
+          # browser()
+          to_validate <- data_r()
+          if (is.reactivevalues(to_validate))
+            out <- lapply(
+              reactiveValuesToList(to_validate),
+              make_validation_alerts) |>
+            purrr::list_flatten()
+
+          if (length(to_validate) > 0) {
+            out <- make_validation_alerts(to_validate)
+          }
+          valid_ui$x <- tagList(out)
+        }
+      )
+
+      output$results <- renderUI({
+        valid_ui$x
+      })
+    }
+  )
+}
+
+
+########################################################################
+############# Validation functions
+########################################################################
+
+#' Dimensions validation
+#'
+#' @param before data before
+#' @param after data after
+#' @param fun dimension function. ncol or nrow
+#'
+#' @returns data.frame
+#'
+dim_change_call <- function(before, after, fun) {
+  # browser()
+  if (!0 %in% c(dim(before), dim(after))) {
+    n_before <- fun(before)
+    n_after <- fun(after)
+    n_out <- n_before - n_after
+    p_after <- n_after / fun(before) * 100
+    p_out <- 100 - p_after
+
+    data.frame(
+      n_before = n_before,
+      n_after = n_after,
+      n_out = n_out,
+      p_after = p_after,
+      p_out = p_out
+    ) |>
+      dplyr::mutate(
+        dplyr::across(
+          dplyr::where(
+            is.numeric
+          ),
+          \(.y) round(.y, 0)
+        )
+      )
+  } else {
+    data.frame(NULL)
+  }
+}
+
+#' Variable filter test wrapper
+#'
+#' @param before data before
+#' @param after data after
+#'
+#' @returns vector
+#'
+#' @examples
+#' vars_filter_validate(mtcars, mtcars[1:6])
+#' vars_filter_validate(mtcars, mtcars[0])
+vars_filter_validate <- function(before, after) {
+  dim_change_call(before, after, ncol)
+}
+
+#' Observations filter test wrapper
+#'
+#' @param before data before
+#' @param after data after
+#'
+#' @returns vector
+#'
+obs_filter_validate <- function(before, after) {
+  dim_change_call(before, after, nrow)
+}
+
+#' Validate function of missingness in data
+#'
+#' @param data data set
+#'
+#' @returns data.frame
+#' @export
+#'
+#' @examples
+#' df <- mtcars
+#' df[1,2:4] <- NA
+#' missings_validate(df)
+missings_validate <- function(data){
+  if (!0 %in% dim(data)) {
+    # browser()
+    p_miss <- sum(is.na(data))/prod(dim(data))*100
+    data.frame(
+      p_miss = p_miss
+    ) |>
+      dplyr::mutate(
+        dplyr::across(
+          dplyr::where(
+            is.numeric
+          ),
+          \(.y) signif(.y, 2)
+        )
+      )
+  } else {
+    data.frame(NULL)
+  }
+}
+
+
+########################################################################
+############# Collected validation functions in a library-like function
+########################################################################
+
+
+#' Validation library
+#'
+#' @param name Index name
+#'
+#' @returns list
+#'
+#' @examples
+#' validation_lib()
+#' validation_lib("missings")
+validation_lib <- function(name=NULL) {
+  ls <- list(
+    "obs_filter" = function(x, y) {
+      ## Validation function for observations filter
+      list(
+        string = i18n$t("You removed {p_out} % of observations."),
+        summary.fun = obs_filter_validate,
+        summary.fun.args = list(
+          before = x,
+          after = y
+        ),
+        test.fun = function(x, var, cut) {
+          test.var <- x[var]
+          ifelse(test.var > cut, "warning", "succes")
+        },
+        test.fun.args = list(var = "p_out", cut = 50)
+      )
+    },
+    "var_filter" = function(x, y) {
+      ## Validation function for variables filter
+      list(
+        string = i18n$t("You removed {p_out} % of variables."),
+        summary.fun = vars_filter_validate,
+        summary.fun.args = list(
+          before = x,
+          after = y
+        ),
+        test.fun = function(x, var, cut) {
+          test.var <- x[var]
+          ifelse(test.var > cut, "warning", "succes")
+        },
+        test.fun.args = list(var = "p_out", cut = 50)
+      )
+    },
+    "missings" = function(x, y) {
+      ### Placeholder for missingness validation
+      list(
+        string = "There are {p_miss} % missing observations.",
+        summary.fun = missings_validate,
+        summary.fun.args = list(
+          data = x
+        ),
+        test.fun = function(x, var, cut) {
+          test.var <- x[var]
+          ifelse(test.var > cut, "warning", "succes")
+        },
+        test.fun.args = list(var = "p_miss", cut = 30)
+      )
+    }
+  )
+
+  if (!is.null(name)){
+    name <- match.arg(name,choices = names(ls))
+    ls[[name]]
+  } else {
+    ls
+  }
+}
+
+
+########################################################################
+############# Validation creation
+########################################################################
+
+#' Create validation data.frame
+#'
+#' @param ls validation list
+#' @param ... magic dots
+#'
+#' @returns data.frame
+#' @export
+#'
+#' @examples
+#' i18n <- shiny.i18n::Translator$new(translation_csvs_path = here::here("inst/translations"))
+#' i18n$set_translation_language("en")
+#' df_original <- mtcars
+#' df_original[1,2:4] <- NA
+#' df_obs <- df_original |> dplyr::filter(carb==4)
+#' df_vars <- df_original[1:7]
+#' val <- purrr::map2(
+#'   .x = validation_lib(),
+#'   .y = list(
+#'   list(x = df_original, y = df_obs),
+#'   list(x = df_original, y = df_vars),
+#'   list(x=df_original)),
+#'   make_validation
+#' )
+#' val |> make_validation_alerts()
+#'
+#' val2 <- purrr::map2(
+#'   .x = validation_lib()[2],
+#'   .y = list(list(x = mtcars, y = mtcars[0])),
+#'   make_validation
+#' )
+#' val2 |> make_validation_alerts()
+#'
+#' val3 <- make_validation(
+#'   ls = validation_lib()[[2]],
+#'   list(x = mtcars, y = mtcars[0])
+#' )
+make_validation <- function(ls, ...) {
+  ls <- do.call(ls, ...)
+
+  df <- do.call(ls$summary.fun, ls$summary.fun.args)
+
+  if (!any(dim(df) == c(0))) {
+    label <- with(df, {
+      glue::glue(ls$string)
+    })
+
+    # browser()
+    status <- do.call(ls$test.fun, modifyList(ls$test.fun.args, list(x = df)))
+
+    data.frame(
+      label = label,
+      status = status[1]
+    )
+  } else {
+    data.frame(NULL)
+  }
+}
+
+
+#' Create alert from validation data.frame
+#'
+#' @param data
+#'
+#' @export
+make_validation_alerts <- function(data) {
+  # browser()
+  if (is.data.frame(data)){
+    ls <- list(data)
+  } else {
+    ls <- data
+  }
+
+  lapply(
+    X = ls,
+    FUN = function(x) {
+      # browser()
+      if (!is.null(dim(x)) && !any(dim(x) == c(0))) {
+        icon <- switch(x$status,
+          "succes" = phosphoricons::ph("check", title = "OK"),
+          "warning" = phosphoricons::ph("warning", title = "Warning")
+        )
+
+        shinyWidgets::alert(
+          icon,
+          htmltools::HTML(x$label),
+          status = x$status,
+          style = "margin-bottom: 10px; padding: 10px;"
+        )
+      } else {
+        return(NULL)
+      }
+    }
+  )
+}
diff --git a/examples/validation_module_demo.R b/examples/validation_module_demo.R
new file mode 100644
index 0000000..b5b6520
--- /dev/null
+++ b/examples/validation_module_demo.R
@@ -0,0 +1,133 @@
+#' Data and analyses validation demo
+#'
+#' @returns
+#' @export
+#'
+#' @examples
+#' \dontrun{
+#' validation_demo_app()
+#' }
+validation_demo_app <- function() {
+  ui <- shiny::fluidPage(
+    shiny::tags$h2("Validation"),
+    IDEAFilter::IDEAFilter_ui("data_filter"),
+    shiny::br(),
+    DT::DTOutput("data_final"),
+    shiny::br(),
+    validation_ui("validation_demo_2")
+  )
+
+  server <- function(input, output, session) {
+    rv <- shiny::reactiveValues(
+      data_original = shiny::reactive(mtcars),
+      data_filtered = NULL
+    )
+
+    rv_validation <- shiny::reactiveValues(
+      obs_filter = NULL,
+      vars_filter = NULL
+    )
+
+    data_filter <- IDEAFilter::IDEAFilter(
+      id = "data_filter",
+      data = mtcars,
+      verbose = TRUE
+    )
+
+    shiny::observeEvent(
+      data_filter(),
+      {
+        rv$data_filtered <- data_filter()
+      }
+    )
+
+    output$data_final <- DT::renderDT(
+      data_filter()
+    )
+
+    shiny::observeEvent(
+      list(
+        data_filter()
+      ),
+      {
+        to_make_validation <- data_filter()
+        ## Validation
+        if (!is.null(to_make_validation)) {
+          validation <-
+            make_validation(
+              ls = validation_lib("obs_filter"),
+              list(
+                x = mtcars,
+                y = to_make_validation
+              )
+            )
+
+        rv_validation$vars_filter <- validation
+
+        validation_server(id = "validation_demo_2", data = rv_validation$vars_filter)
+
+        }
+
+
+      }
+    )
+
+    # shiny::observeEvent(
+    #   list(
+    #     shiny::reactive(rv_validation$vars_filter)(),
+    #     data_filter()
+    #   ),
+    #   {
+    #     # browser()
+    #     # to_make_alert <- shiny::isolate(rv_validation$vars_filter)
+    #     to_make_alert <- shiny::reactive(rv_validation$vars_filter)()
+    #     if (!is.null(rv_validation$vars_filter)) {
+    #       validation_server(id = "validation_demo_2", data = to_make_alert)
+    #     }
+    #   }
+    # )
+  }
+  shiny::shinyApp(ui, server)
+}
+
+
+#' Title
+#'
+#' @returns
+#' @export
+#'
+#' @examples
+#' validation_nr_demo_app()
+validation_nr_demo_app <- function() {
+  ui <- shiny::fluidPage(
+    shiny::tags$h2("Validation"),
+    shiny::br(),
+    validation_ui("validation_demo_1", max_height = "30px"),
+    shiny::br(),
+    validation_ui("validation_demo_2")
+  )
+
+  server <- function(input, output, session) {
+    df_original <- mtcars
+
+    df_obs <- mtcars |> dplyr::filter(mpg > 20)
+
+    df_vars <- df_obs[1:6]
+
+    val1 <- purrr::map2(
+      .x = validation_lib()[1],
+      .y = list(list(x = df_original, y = df_obs)),
+      make_validation
+    )
+
+    val2 <- make_validation(
+      ls = validation_lib()[[2]],
+      list(x = df_original, y = df_vars)
+    )
+
+    validation_server(id = "validation_demo_1", data = val1)
+
+    validation_server(id = "validation_demo_2", data = val2)
+  }
+  shiny::shinyApp(ui, server)
+}
diff --git a/man/validation.Rd b/man/validation.Rd
new file mode 100644
index 0000000..032ecd8
--- /dev/null
+++ b/man/validation.Rd
@@ -0,0 +1,169 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/validation.R
+\name{validation_ui}
+\alias{validation_ui}
+\alias{validation_server}
+\title{Validation module}
+\usage{
+validation_ui(id, max_height = NULL, ...)
+
+validation_server(id, data)
+}
+\arguments{
+\item{id}{Module's ID.}
+
+\item{max_height}{Maximum height for validation results element, useful if you have many rules.}
+
+\item{...}{Arguments passed to \code{actionButton} or \code{uiOutput} depending on display mode,
+you cannot use \code{inputId}/\code{outputId}, \code{label} or \code{icon} (button only).}
+
+\item{data}{a \code{reactive} function returning a \code{data.frame}.}
+}
+\value{
+\itemize{
+\item UI: HTML tags that can be included in shiny's UI
+\item Server: a \code{list} with two slots:
+\itemize{
+\item \strong{status}: a \code{reactive} function returning the best status available between \code{"OK"}, \code{"Failed"} or \code{"Error"}.
+\item \strong{details}: a \code{reactive} function returning a \code{list} with validation details.
+}
+}
+}
+\description{
+Check that a dataset respect some validation expectations.
+}
+\examples{
+#' Data and analyses validation demo
+#'
+#' @returns
+#' @export
+#'
+#' @examples
+#' \dontrun{
+#' validation_demo_app()
+#' }
+validation_demo_app <- function() {
+  ui <- shiny::fluidPage(
+    shiny::tags$h2("Validation"),
+    IDEAFilter::IDEAFilter_ui("data_filter"),
+    shiny::br(),
+    DT::DTOutput("data_final"),
+    shiny::br(),
+    validation_ui("validation_demo_2")
+  )
+
+  server <- function(input, output, session) {
+    rv <- shiny::reactiveValues(
+      data_original = shiny::reactive(mtcars),
+      data_filtered = NULL
+    )
+
+    rv_validation <- shiny::reactiveValues(
+      obs_filter = NULL,
+      vars_filter = NULL
+    )
+
+    data_filter <- IDEAFilter::IDEAFilter(
+      id = "data_filter",
+      data = mtcars,
+      verbose = TRUE
+    )
+
+    shiny::observeEvent(
+      data_filter(),
+      {
+        rv$data_filtered <- data_filter()
+      }
+    )
+
+    output$data_final <- DT::renderDT(
+      data_filter()
+    )
+
+    shiny::observeEvent(
+      list(
+        data_filter()
+      ),
+      {
+        to_make_validation <- data_filter()
+        ## Validation
+        if (!is.null(to_make_validation)) {
+          validation <-
+            make_validation(
+              ls = validation_lib("obs_filter"),
+              list(
+                x = mtcars,
+                y = to_make_validation
+              )
+            )
+
+        rv_validation$vars_filter <- validation
+
+        validation_server(id = "validation_demo_2", data = rv_validation$vars_filter)
+
+        }
+
+
+      }
+    )
+
+    # shiny::observeEvent(
+    #   list(
+    #     shiny::reactive(rv_validation$vars_filter)(),
+    #     data_filter()
+    #   ),
+    #   {
+    #     # browser()
+    #     # to_make_alert <- shiny::isolate(rv_validation$vars_filter)
+    #     to_make_alert <- shiny::reactive(rv_validation$vars_filter)()
+    #     if (!is.null(rv_validation$vars_filter)) {
+    #       validation_server(id = "validation_demo_2", data = to_make_alert)
+    #     }
+    #   }
+    # )
+  }
+  shiny::shinyApp(ui, server)
+}
+
+
+#' Title
+#'
+#' @returns
+#' @export
+#'
+#' @examples
+#' validation_nr_demo_app()
+validation_nr_demo_app <- function() {
+  ui <- shiny::fluidPage(
+    shiny::tags$h2("Validation"),
+    shiny::br(),
+    validation_ui("validation_demo_1", max_height = "30px"),
+    shiny::br(),
+    validation_ui("validation_demo_2")
+  )
+
+  server <- function(input, output, session) {
+    df_original <- mtcars
+
+    df_obs <- mtcars |> dplyr::filter(mpg > 20)
+
+    df_vars <- df_obs[1:6]
+
+    val1 <- purrr::map2(
+      .x = validation_lib()[1],
+      .y = list(list(x = df_original, y = df_obs)),
+      make_validation
+    )
+
+    val2 <- make_validation(
+      ls = validation_lib()[[2]],
+      list(x = df_original, y = df_vars)
+    )
+
+    validation_server(id = "validation_demo_1", data = val1)
+
+    validation_server(id = "validation_demo_2", data = val2)
+  }
+  shiny::shinyApp(ui, server)
+}
+}
diff --git a/man/validation_lib.Rd b/man/validation_lib.Rd
new file mode 100644
index 0000000..86b454f
--- /dev/null
+++ b/man/validation_lib.Rd
@@ -0,0 +1,21 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/validation.R
+\name{validation_lib}
+\alias{validation_lib}
+\title{Validation library}
+\usage{
+validation_lib(name = NULL)
+}
+\arguments{
+\item{name}{Index name}
+}
+\value{
+list
+}
+\description{
+Validation library
+}
+\examples{
+validation_lib()
+validation_lib("missings")
+}
diff --git a/man/vars_filter_validate.Rd b/man/vars_filter_validate.Rd
new file mode 100644
index 0000000..1e902bd
--- /dev/null
+++ b/man/vars_filter_validate.Rd
@@ -0,0 +1,23 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/validation.R
+\name{vars_filter_validate}
+\alias{vars_filter_validate}
+\title{Variable filter test wrapper}
+\usage{
+vars_filter_validate(before, after)
+}
+\arguments{
+\item{before}{data before}
+
+\item{after}{data after}
+}
+\value{
+vector
+}
+\description{
+Variable filter test wrapper
+}
+\examples{
+vars_filter_validate(mtcars, mtcars[1:6])
+vars_filter_validate(mtcars, mtcars[0])
+}