diff --git a/DESCRIPTION b/DESCRIPTION
index 7ad4c6b7..e4da849c 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,6 +1,6 @@
 Package: blockr
 Title: A block-based framework for data manipulation and visualization
-Version: 0.0.2.9031
+Version: 0.0.3.9000
 Authors@R: 
     c(person(given = "Nicolas",
              family = "Bennett",
@@ -42,7 +42,8 @@ Imports:
     shinyWidgets
 Remotes:
     DivadNojnarg/DiagrammeR,
-    BristolMyersSquibb/blockr.data
+    BristolMyersSquibb/blockr.data,
+    cynkra/scoutbaR
 Suggests: 
     knitr,
     rmarkdown,
@@ -55,7 +56,8 @@ Suggests:
     ggplot2,
     vdiffr,
     palmerpenguins,
-    blockr.data
+    blockr.data,
+    scoutbaR
 Config/testthat/edition: 3
 VignetteBuilder: knitr
 Depends: 
diff --git a/NAMESPACE b/NAMESPACE
index 4ed32af5..a8f34c68 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -16,6 +16,15 @@ S3method(block_icon,data_block)
 S3method(block_icon,default)
 S3method(block_icon,plot_block)
 S3method(block_icon,transform_block)
+S3method(block_input_check,data_block)
+S3method(block_input_check,parser_block)
+S3method(block_input_check,result_block)
+S3method(block_input_check,transform_block)
+S3method(block_output_ptype,dataset_block)
+S3method(block_output_ptype,filesbrowser_block)
+S3method(block_output_ptype,result_block)
+S3method(block_output_ptype,transform_block)
+S3method(block_output_ptype,upload_block)
 S3method(blockr_serialize,block)
 S3method(blockr_serialize,field)
 S3method(blockr_serialize,stack)
@@ -148,7 +157,9 @@ export(block_combiner)
 export(block_descr)
 export(block_header)
 export(block_icon)
+export(block_input_check)
 export(block_name)
+export(block_output_ptype)
 export(blockr_deserialize)
 export(blockr_serialize)
 export(cat_logger)
@@ -166,7 +177,6 @@ export(generate_server)
 export(generate_ui)
 export(get_compatible_blocks)
 export(get_field_name)
-export(get_registry)
 export(get_stack_name)
 export(get_stack_title)
 export(get_workspace)
@@ -180,6 +190,7 @@ export(init_lock)
 export(initialize_block)
 export(initialize_field)
 export(inject_remove_button)
+export(input_failure)
 export(input_ids)
 export(is_block)
 export(is_field)
diff --git a/NEWS.md b/NEWS.md
index f6f2e77c..4bc95d5c 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,3 +1,47 @@
+# blockr 0.0.3.9000
+
+## Breaking changes
+- `register_blocks()` and `register_block()` __input__, __output__ have been changed. If your package is composed of __data__ or __transform__ blocks, nothing has to be done, expect removing the old registration API. If you developed custom blocks, whose classes are neither __data__ or __transform__, you'll have to develop a type checker like so, for a plot block:
+
+```r
+block_input_check.plot_block <- function(x, data, ...) {
+
+  if (inherits(data, "data.frame")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting data.frame input.")
+}
+
+block_output_ptype.plot_block <- function(x, ...) ggplot()
+```
+
+Besides, there is no need to specify the __classes__ as this is automatically retrieved from the constructed block.
+As a consequence, the new registration looks like:
+
+```r
+# NEW
+register_block(
+  constructor = new_ggplot_block,
+  name = "ggplot",
+  description = "Initialise a ggplot2 plot",
+  category = "Plot",
+  package = pkg
+)
+
+# OLD
+register_block(
+  constructor = new_ggplot_block,
+  name = "ggplot",
+  description = "Initialise a ggplot2 plot",
+  classes = c("ggplot_block", "plot_block"),
+  input = "plot",
+  output = "plot",
+  category = "Plot",
+  package = pkg
+)
+```
+
 # blockr 0.0.2.9031
 
 ## Feature
diff --git a/R/block-core.R b/R/block-core.R
index 452b6366..87858d5c 100644
--- a/R/block-core.R
+++ b/R/block-core.R
@@ -312,3 +312,89 @@ update_fields.transform_block <- function(x, session, data, ...) {
 #' @rdname update_fields
 #' @export
 update_fields.plot_block <- update_fields.transform_block
+
+#' Block input/output
+#'
+#' Used for checking whether blocks are compatible
+#'
+#' @param x Block
+#' @param data Input data.
+#' @param ... For generic consistency.
+#' @rdname block_io
+#' @export
+block_input_check <- function(x, data, ...) UseMethod("block_input_check")
+
+#' @rdname block_io
+#' @export
+block_input_check.data_block <- function(x, data, ...) {
+
+  if (missing(data) || is.null(data)) {
+    return(invisible(NULL))
+  }
+
+  input_failure("No (or empty) input expected.")
+}
+
+#' @rdname block_io
+#' @export
+block_input_check.transform_block <- function(x, data, ...) {
+
+  if (inherits(data, "data.frame")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting data.frame input.")
+}
+
+#' @rdname block_io
+#' @export
+block_input_check.parser_block <- function(x, data, ...) {
+
+  if (is_string(data)) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting string-valued input.")
+}
+
+#' @rdname block_io
+#' @export
+block_input_check.result_block <- function(x, data, ...) {
+
+  if (length(get_workspace_stacks()) <= 1L) {
+    input_failure("Expecting at least two stacks.")
+  }
+
+  NextMethod()
+}
+
+#' @rdname block_io
+#' @param class Custom class
+#' @export
+input_failure <- function(..., class = character()) {
+  rlang::abort(paste0(...), class = c(class, "input_failure"))
+}
+
+#' @rdname block_io
+#' @export
+block_output_ptype <- function(x, ...) UseMethod("block_output_ptype")
+
+#' @rdname block_io
+#' @export
+block_output_ptype.dataset_block <- function(x, ...) data.frame()
+
+#' @rdname block_io
+#' @export
+block_output_ptype.result_block <- function(x, ...) value(x[["stack"]])
+
+#' @rdname block_io
+#' @export
+block_output_ptype.upload_block <- function(x, ...) character(1L)
+
+#' @rdname block_io
+#' @export
+block_output_ptype.filesbrowser_block <- function(x, ...) character(1L)
+
+#' @rdname block_io
+#' @export
+block_output_ptype.transform_block <- function(x, ...) data.frame()
diff --git a/R/registry.R b/R/registry.R
index 938190bb..eef1ab7c 100644
--- a/R/registry.R
+++ b/R/registry.R
@@ -38,18 +38,16 @@ block_name <- block_descrs_getter(block_descr_getter("name"))
 #' @export
 block_descr <- block_descrs_getter(block_descr_getter("description"))
 
-new_block_descr <- function(constructor, name, description, classes, input,
+new_block_descr <- function(constructor, name, description, id, classes, input,
                             output, pkg, category) {
   stopifnot(
     is.function(constructor), is_string(name), is_string(description),
-    is_string(category),
-    is.character(classes), length(classes) >= 1L,
-    is_string(input), is_string(output), is_string(pkg)
+    is_string(category), is.character(classes), length(classes) >= 1L,
+    is.function(input), is_string(pkg), is_string(id)
   )
 
   structure(
-    constructor,
-    name = name, description = description,
+    constructor, name = name, description = description, id = id,
     classes = classes, input = input, output = output,
     package = pkg, category = category, class = "block_descr"
   )
@@ -62,6 +60,8 @@ block_registry <- new.env()
 #' @param classes Block classes
 #' @param input,output Object types the block consumes and produces
 #' @param package Package where block is defined
+#' @param ptype Block ptype
+#' @param id Block registry ID
 #' @param category Useful to sort blocks by topics. If not specified,
 #' blocks are uncategorized.
 #'
@@ -71,18 +71,25 @@ register_block <- function(
     constructor,
     name,
     description,
-    classes,
-    input,
-    output,
+    ptype = constructor(),
+    classes = class(ptype),
+    input = get_s3_method("block_input_check", ptype),
+    output = block_output_ptype(ptype),
+    id = classes[1L],
     package = NA_character_,
     category = "uncategorized") {
+
   descr <- new_block_descr(
-    constructor, name, description, classes, input,
-    output, package, category
+    constructor,
+    name,
+    description,
+    id, classes,
+    input,
+    output,
+    package,
+    category
   )
 
-  id <- classes[1L]
-
   if (id %in% list_blocks()) {
     warning("block ", id, " already exists and will be overwritten.")
   }
@@ -90,35 +97,40 @@ register_block <- function(
   assign(id, descr, envir = block_registry)
 }
 
+get_s3_method <- function(generic, obj) {
+
+  for (cls in class(obj)) {
+    res <- try(utils::getS3method("block_input_check", cls), silent = TRUE)
+    if (!inherits(res, "try-error")) {
+      return(res)
+    }
+  }
+
+  stop("no method found for generic ", generic, " and classes ",
+       paste0(class(obj), collapse = ", "))
+}
+
 #' @param ... Forwarded to `register_block()`
 #' @rdname available_blocks
 #' @export
-register_blocks <- function(
-    constructor,
-    name,
-    description,
-    classes,
-    input,
-    output,
-    package = NA_character_,
-    category = "uncategorized") {
-  if (length(constructor) == 1L && !is.list(classes)) {
-    classes <- list(classes)
+register_blocks <- function(...) {
+
+  arg_processor <- function(constructor, ...) {
+
+    wrap_list <- function(x) {
+      if (length(x) > 1L) list(x) else x
+    }
+
+    if (length(constructor) > 1L) {
+      return(c(list(constructor), list(...)))
+    }
+
+    c(list(constructor), lapply(list(...), wrap_list))
   }
 
-  res <- Map(
-    register_block,
-    constructor = constructor,
-    name = name,
-    description = description,
-    classes = classes,
-    input = input,
-    output = output,
-    package = package,
-    category = category
+  invisible(
+    do.call(Map, c(register_block, arg_processor(...)))
   )
-
-  invisible(res)
 }
 
 list_blocks <- function() {
@@ -212,60 +224,6 @@ register_blockr_blocks <- function(pkg) {
       "Select n first rows of dataset",
       "Mutate block"
     ),
-    classes = list(
-      c("dataset_block", "data_block"),
-      c("result_block", "data_block"),
-      c("upload_block", "data_block"),
-      c("filesbrowser_block", "data_block"),
-      c("csv_block", "parser_block", "transform_block"),
-      c("rds_block", "parser_block", "transform_block"),
-      c("json_block", "parser_block", "transform_block"),
-      c("xpt_block", "parser_block", "transform_block"),
-      c("filter_block", "transform_block"),
-      c("select_block", "transform_block"),
-      c("summarize_block", "transform_block"),
-      c("arrange_block", "transform_block"),
-      c("group_by_block", "transform_block"),
-      c("join_block", "transform_block"),
-      c("head_block", "transform_block"),
-      c("mutate_block", "transform_block")
-    ),
-    input = c(
-      NA_character_,
-      NA_character_,
-      NA_character_,
-      NA_character_,
-      "string",
-      "string",
-      "string",
-      "string",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame"
-    ),
-    output = c(
-      "data.frame",
-      "data.frame",
-      "string",
-      "string",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame",
-      "data.frame"
-    ),
     package = pkg,
     category = c(
       "data",
@@ -292,6 +250,7 @@ register_blockr_blocks <- function(pkg) {
 #' @rdname available_blocks
 #' @export
 construct_block <- function(block, ...) {
+
   if (is_string(block)) {
     block <- get_block_descr(block)
   }
@@ -301,29 +260,40 @@ construct_block <- function(block, ...) {
   block(...)
 }
 
-#' List available blocks as a data.frame
+are_blocks_compatible <- function(x, y) {
+
+  stopifnot(inherits(x, "block_descr"))
+
+  tryCatch(
+    {
+      attr(x, "input")(x(), y)
+      TRUE
+    },
+    input_failure = function(e) {
+      structure(FALSE, msg = conditionMessage(e))
+    }
+  )
+}
+
+#' Find stack compatible blocks
 #'
-#' Provides an alternate way of displaying
-#' the registry information.
-#' This can be useful to create dynamic UI elements
-#' like in \link{add_block_ui}.
+#' Given a stack, we use the registry to find
+#' what are the blocks compatible with the last stack block.
+#' If the stack is empy, we return data blocks.
 #'
-#' @return A dataframe.
+#' @param stack Stack object.
+#'
+#' @return a dataframe.
 #'
 #' @export
-get_registry <- function() {
-  res <- lapply(seq_along(available_blocks()), \(i) {
-    blk <- available_blocks()[[i]]
-    attrs <- attributes(blk)
-    data.frame(
-      ctor = names(available_blocks())[[i]],
-      description = attrs[["description"]],
-      category = attrs[["category"]],
-      classes = paste(c(attrs[["classes"]], "block"), collapse = ", "),
-      input = attrs[["input"]],
-      output = attrs[["output"]],
-      package = attrs[["package"]]
-    )
-  })
-  do.call(rbind, res)
+get_compatible_blocks <- function(stack) {
+
+  if (length(stack)) {
+    dat <- block_output_ptype(stack[[length(stack)]])
+  } else {
+    dat <- NULL
+  }
+
+  blocks <- available_blocks()
+  blocks[lgl_ply(blocks, are_blocks_compatible, dat)]
 }
diff --git a/R/server.R b/R/server.R
index 70653199..3f7f4d75 100644
--- a/R/server.R
+++ b/R/server.R
@@ -210,8 +210,9 @@ generate_server_block <- function(
       out_dat <- if (attr(x, "submit") > -1) {
         eventReactive(input$submit,
           {
-            req(is_valid$block)
-            if (is.null(in_dat())) {
+            if (!isTruthy(is_valid$block)) {
+              block_output_ptype(blk())
+            } else if (is.null(in_dat())) {
               evaluate_block(blk())
             } else {
               evaluate_block(blk(), data = in_dat())
@@ -223,8 +224,9 @@ generate_server_block <- function(
         )
       } else {
         reactive({
-          req(is_valid$block)
-          if (is.null(in_dat()) && !inherits(x, "transform_block")) {
+          if (!isTruthy(is_valid$block)) {
+            block_output_ptype(blk())
+          } else if (is.null(in_dat()) && !inherits(x, "transform_block")) {
             evaluate_block(blk())
           } else {
             evaluate_block(blk(), data = in_dat())
@@ -522,14 +524,20 @@ add_block_server.default <- function(x, id, vals, ...) {
         blk_choices(get_compatible_blocks(vals$stack))
 
         choices <- blk_choices()
-        choices$name <- paste(choices$package, sep = "::", choices$ctor)
+
+        choices <- lapply(
+          set_names(nm = c("name", "package", "id", "category", "description")),
+          function(x) chr_ply(choices, attr, x)
+        )
+
+        choices$name <- paste0(choices$name, " (", choices$package, ")")
 
         shinyWidgets::updateVirtualSelect(
           "search",
           choices = shinyWidgets::prepare_choices(
-            choices,
+            as.data.frame(choices),
             .data$name,
-            .data$ctor,
+            .data$id,
             group_by = .data$category,
             description = .data$description
           )
diff --git a/R/stack.R b/R/stack.R
index 8a7ae563..2024bbe6 100644
--- a/R/stack.R
+++ b/R/stack.R
@@ -248,13 +248,13 @@ add_block <- function(stack, block, position = NULL) {
   if (!length(stack)) {
 
     tmp <- initialize_block(
-      do.call(block, list())
+      construct_block(block)
     )
 
   } else {
 
     tmp <- initialize_block(
-      do.call(block, list(position = position)),
+      construct_block(block, position = position),
       data
     )
   }
@@ -262,45 +262,6 @@ add_block <- function(stack, block, position = NULL) {
   set_stack_blocks(stack, append(stack, list(tmp), position), data)
 }
 
-#' Find stack compatible blocks
-#'
-#' Given a stack, we use the registry to find
-#' what are the blocks compatible with the last stack block.
-#' If the stack is empy, we return data blocks.
-#'
-#' @param stack Stack object.
-#'
-#' @return a dataframe.
-#'
-#' @export
-get_compatible_blocks <- function(stack) {
-  registry <- get_registry()
-  # Only data blocks can be used for a 0 length stack
-  if (length(stack) == 0) {
-    tmp <- registry[is.na(registry$input), ]
-    # Drop result block if there are no other stacks
-    if (length(get_workspace_stacks()) <= 1) {
-      tmp <- tmp[tmp$ctor != "result_block", ]
-    }
-    return(tmp)
-  }
-  # Otherwise we compare the output of the last block
-  # and propose any of the block that have compatible input
-  cls <- paste(class(stack[[length(stack)]]), collapse = ", ")
-  last_blk_output <- registry[grep(cls, registry$classes), "output"]
-
-  tmp <- registry[!is.na(registry$input) & registry$input == last_blk_output, ]
-
-  # Insert result block if there are other stacks
-  if (length(get_workspace_stacks()) > 1) {
-    tmp <- rbind(
-      registry[registry$ctor == "result_block", ],
-      tmp
-    )
-  }
-  tmp
-}
-
 #' @param stack An object inheriting form `"stack"`
 #' @param id Stack ID
 #'
diff --git a/R/sysdata.rda b/R/sysdata.rda
index 42616776..53a7d360 100644
Binary files a/R/sysdata.rda and b/R/sysdata.rda differ
diff --git a/_pkgdown.yml b/_pkgdown.yml
index 978229fb..cac08513 100644
--- a/_pkgdown.yml
+++ b/_pkgdown.yml
@@ -144,6 +144,8 @@ reference:
   - "`get_registry`"
   - "`add_block_ui`"
   - "`add_block_server`"
+  - "`block_input_check`"
+  - "`block_output_ptype`"
 
 - title: Server utilities
   desc: Shiny server elements
@@ -206,6 +208,7 @@ reference:
 
 news:
  releases:
+ - text: "blockr 0.0.3.9000"
  - text: "blockr 0.0.2.9031"
  - text: "blockr 0.0.2"
  - text: "blockr 0.0.1.9000"
diff --git a/inst/shinylive/apps/ae-forest-plot/app.R b/inst/shinylive/apps/ae-forest-plot/app.R
index c778c670..d74ce8b4 100644
--- a/inst/shinylive/apps/ae-forest-plot/app.R
+++ b/inst/shinylive/apps/ae-forest-plot/app.R
@@ -139,14 +139,22 @@ new_forest_plot_block <- function(...) {
   )
 }
 
+block_input_check.plot_block <- function(x, data, ...) {
+
+  if (inherits(data, "data.frame")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting data.frame input.")
+}
+
+block_output_ptype.plot_block <- function(x, ...) ggplot()
+
 # Register the custom block
 register_block(
   new_forest_plot_block,
   name = "Adverse Event Forest Plot",
-  description = "Create a forest plot of adverse events comparing two treatment arms",
-  classes = c("adverse_event_plot_block", "plot_block"),
-  input = "data.frame",
-  output = "plot"
+  description = "Create a forest plot of adverse events comparing two treatment arms"
 )
 
 # Create the stack
diff --git a/inst/shinylive/apps/ggplot-block/app.R b/inst/shinylive/apps/ggplot-block/app.R
index 372d6fd6..4ecbd068 100644
--- a/inst/shinylive/apps/ggplot-block/app.R
+++ b/inst/shinylive/apps/ggplot-block/app.R
@@ -38,6 +38,38 @@ new_geompoint_block <- function(color = character(), shape = character(), ...) {
   )
 }
 
+block_input_check.plot_block <- function(x, data, ...) {
+
+  if (inherits(data, "data.frame")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting data.frame input.")
+}
+
+block_output_ptype.plot_block <- function(x, ...) ggplot()
+
+block_input_check.plot_layer_block <- function(x, data, ...) {
+  if (inherits(data, "ggplot")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting ggplot input.")
+}
+
+block_output_ptype.plot_layer_block <- function(x, ...) ggplot()
+
+register_blocks(
+  constructor = c(new_ggplot_block, new_geompoint_block),
+  name = c("ggplot block", "geompoint block"),
+  description = c(
+    "Builds a ggplot object",
+    "Add points geom to ggplot object"
+  ),
+  package = "blockr.demo",
+  category = c("Visualization", "Visualization")
+)
+
 stack <- new_stack(
   data_block = new_dataset_block("penguins", "palmerpenguins"),
   plot_block = new_ggplot_block("flipper_length_mm", "body_mass_g"),
diff --git a/inst/shinylive/apps/palmer-penguins/app.R b/inst/shinylive/apps/palmer-penguins/app.R
index 3fdffe4b..42595c42 100644
--- a/inst/shinylive/apps/palmer-penguins/app.R
+++ b/inst/shinylive/apps/palmer-penguins/app.R
@@ -38,9 +38,41 @@ new_geompoint_block <- function(color = character(), shape = character(), ...) {
   )
 }
 
+block_input_check.plot_block <- function(x, data, ...) {
+
+  if (inherits(data, "data.frame")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting data.frame input.")
+}
+
+block_output_ptype.plot_block <- function(x, ...) ggplot()
+
+block_input_check.plot_layer_block <- function(x, data, ...) {
+  if (inherits(data, "ggplot")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting ggplot input.")
+}
+
+block_output_ptype.plot_layer_block <- function(x, ...) ggplot()
+
+register_blocks(
+  constructor = c(new_ggplot_block, new_geompoint_block),
+  name = c("ggplot block", "geompoint block"),
+  description = c(
+    "Builds a ggplot object",
+    "Add points geom to ggplot object"
+  ),
+  package = "blockr.demo",
+  category = c("Visualization", "Visualization")
+)
+
 stack <- new_stack(
   data_block = new_dataset_block("penguins", "palmerpenguins"),
-  filter_block = new_filter_block("sex", "female"),
+  filter_block = new_filter_block("sex", "female", submit = TRUE),
   plot_block = new_ggplot_block("flipper_length_mm", "body_mass_g"),
   layer_block = new_geompoint_block("species", "species")
 )
diff --git a/inst/shinylive/apps/registry-demo/app.R b/inst/shinylive/apps/registry-demo/app.R
index 2601680c..b02fa557 100644
--- a/inst/shinylive/apps/registry-demo/app.R
+++ b/inst/shinylive/apps/registry-demo/app.R
@@ -19,10 +19,7 @@ new_tail_block <- function(data, n_rows = numeric(), ...) {
 register_block(
   constructor = new_tail_block,
   name = "tail block",
-  description = "return last n rows",
-  classes = c("tail_block", "transform_block"),
-  input = "data.frame",
-  output = "data.frame"
+  description = "return last n rows"
 )
 
 stack <- new_stack(new_dataset_block)
diff --git a/inst/testdata/test.registry/R/zzz.R b/inst/testdata/test.registry/R/zzz.R
index ab799814..b7abf67e 100644
--- a/inst/testdata/test.registry/R/zzz.R
+++ b/inst/testdata/test.registry/R/zzz.R
@@ -5,9 +5,6 @@
     name = "dummy block",
     description = "Returns input dataset",
     category = "transform",
-    classes = c("dummy_block", "transform_block"),
-    input = "data.frame",
-    output = "data.frame",
     package = pkgname
   )
 
diff --git a/man/available_blocks.Rd b/man/available_blocks.Rd
index d2777f30..4bd97120 100644
--- a/man/available_blocks.Rd
+++ b/man/available_blocks.Rd
@@ -20,23 +20,16 @@ register_block(
   constructor,
   name,
   description,
-  classes,
-  input,
-  output,
+  ptype = constructor(),
+  classes = class(ptype),
+  input = get_s3_method("block_input_check", ptype),
+  output = block_output_ptype(ptype),
+  id = classes[1L],
   package = NA_character_,
   category = "uncategorized"
 )
 
-register_blocks(
-  constructor,
-  name,
-  description,
-  classes,
-  input,
-  output,
-  package = NA_character_,
-  category = "uncategorized"
-)
+register_blocks(...)
 
 unregister_blocks(ids = NULL, package = NULL)
 
@@ -49,20 +42,24 @@ construct_block(block, ...)
 
 \item{name, description}{Metadata describing the block}
 
+\item{ptype}{Block ptype}
+
 \item{classes}{Block classes}
 
 \item{input, output}{Object types the block consumes and produces}
 
+\item{id}{Block registry ID}
+
 \item{package}{Package where block is defined}
 
 \item{category}{Useful to sort blocks by topics. If not specified,
 blocks are uncategorized.}
 
+\item{...}{Forwarded to \code{register_block()}}
+
 \item{ids}{Character vector of block IDs (first entry in class attribute)}
 
 \item{block}{Block name or description object}
-
-\item{...}{Forwarded to \code{register_block()}}
 }
 \description{
 List available blocks.
diff --git a/man/block_io.Rd b/man/block_io.Rd
new file mode 100644
index 00000000..0b93f9b2
--- /dev/null
+++ b/man/block_io.Rd
@@ -0,0 +1,53 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/block-core.R
+\name{block_input_check}
+\alias{block_input_check}
+\alias{block_input_check.data_block}
+\alias{block_input_check.transform_block}
+\alias{block_input_check.parser_block}
+\alias{block_input_check.result_block}
+\alias{input_failure}
+\alias{block_output_ptype}
+\alias{block_output_ptype.dataset_block}
+\alias{block_output_ptype.result_block}
+\alias{block_output_ptype.upload_block}
+\alias{block_output_ptype.filesbrowser_block}
+\alias{block_output_ptype.transform_block}
+\title{Block input/output}
+\usage{
+block_input_check(x, data, ...)
+
+\method{block_input_check}{data_block}(x, data, ...)
+
+\method{block_input_check}{transform_block}(x, data, ...)
+
+\method{block_input_check}{parser_block}(x, data, ...)
+
+\method{block_input_check}{result_block}(x, data, ...)
+
+input_failure(..., class = character())
+
+block_output_ptype(x, ...)
+
+\method{block_output_ptype}{dataset_block}(x, ...)
+
+\method{block_output_ptype}{result_block}(x, ...)
+
+\method{block_output_ptype}{upload_block}(x, ...)
+
+\method{block_output_ptype}{filesbrowser_block}(x, ...)
+
+\method{block_output_ptype}{transform_block}(x, ...)
+}
+\arguments{
+\item{x}{Block}
+
+\item{data}{Input data.}
+
+\item{...}{For generic consistency.}
+
+\item{class}{Custom class}
+}
+\description{
+Used for checking whether blocks are compatible
+}
diff --git a/man/get_compatible_blocks.Rd b/man/get_compatible_blocks.Rd
index b0f3ce2a..0313a424 100644
--- a/man/get_compatible_blocks.Rd
+++ b/man/get_compatible_blocks.Rd
@@ -1,5 +1,5 @@
 % Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/stack.R
+% Please edit documentation in R/registry.R
 \name{get_compatible_blocks}
 \alias{get_compatible_blocks}
 \title{Find stack compatible blocks}
diff --git a/man/get_registry.Rd b/man/get_registry.Rd
deleted file mode 100644
index 812d0421..00000000
--- a/man/get_registry.Rd
+++ /dev/null
@@ -1,17 +0,0 @@
-% Generated by roxygen2: do not edit by hand
-% Please edit documentation in R/registry.R
-\name{get_registry}
-\alias{get_registry}
-\title{List available blocks as a data.frame}
-\usage{
-get_registry()
-}
-\value{
-A dataframe.
-}
-\description{
-Provides an alternate way of displaying
-the registry information.
-This can be useful to create dynamic UI elements
-like in \link{add_block_ui}.
-}
diff --git a/tests/testthat/_snaps/block/block-app-001_.new.png b/tests/testthat/_snaps/block/block-app-001_.new.png
index 63396905..74be8a30 100644
Binary files a/tests/testthat/_snaps/block/block-app-001_.new.png and b/tests/testthat/_snaps/block/block-app-001_.new.png differ
diff --git a/tests/testthat/_snaps/block/block-app-002_.new.png b/tests/testthat/_snaps/block/block-app-002_.new.png
index 88e2cad6..d196cc23 100644
Binary files a/tests/testthat/_snaps/block/block-app-002_.new.png and b/tests/testthat/_snaps/block/block-app-002_.new.png differ
diff --git a/tests/testthat/_snaps/block/block-app-003_.new.png b/tests/testthat/_snaps/block/block-app-003_.new.png
index b4d056ed..c5d76266 100644
Binary files a/tests/testthat/_snaps/block/block-app-003_.new.png and b/tests/testthat/_snaps/block/block-app-003_.new.png differ
diff --git a/tests/testthat/_snaps/block/block-app-004_.new.png b/tests/testthat/_snaps/block/block-app-004_.new.png
index 7cf37837..aa52392f 100644
Binary files a/tests/testthat/_snaps/block/block-app-004_.new.png and b/tests/testthat/_snaps/block/block-app-004_.new.png differ
diff --git a/tests/testthat/_snaps/block/block-app-005_.new.png b/tests/testthat/_snaps/block/block-app-005_.new.png
index f5ae933a..30bec99f 100644
Binary files a/tests/testthat/_snaps/block/block-app-005_.new.png and b/tests/testthat/_snaps/block/block-app-005_.new.png differ
diff --git a/tests/testthat/_snaps/result/result-app-001_.new.png b/tests/testthat/_snaps/result/result-app-001_.new.png
index e9b0d0c5..45c5c9b2 100644
Binary files a/tests/testthat/_snaps/result/result-app-001_.new.png and b/tests/testthat/_snaps/result/result-app-001_.new.png differ
diff --git a/tests/testthat/_snaps/stack/stack-app-001_.png b/tests/testthat/_snaps/stack/stack-app-001_.png
index f5ae933a..30bec99f 100644
Binary files a/tests/testthat/_snaps/stack/stack-app-001_.png and b/tests/testthat/_snaps/stack/stack-app-001_.png differ
diff --git a/tests/testthat/_snaps/stack/stack-app-002_.new.png b/tests/testthat/_snaps/stack/stack-app-002_.new.png
deleted file mode 100644
index 6b451e7f..00000000
Binary files a/tests/testthat/_snaps/stack/stack-app-002_.new.png and /dev/null differ
diff --git a/tests/testthat/_snaps/stack/stack-app-002_.png b/tests/testthat/_snaps/stack/stack-app-002_.png
index d28a2e6a..8e0e0892 100644
Binary files a/tests/testthat/_snaps/stack/stack-app-002_.png and b/tests/testthat/_snaps/stack/stack-app-002_.png differ
diff --git a/tests/testthat/_snaps/stack/stack-app-003.json b/tests/testthat/_snaps/stack/stack-app-003.json
index 8819cc6c..af565436 100644
--- a/tests/testthat/_snaps/stack/stack-app-003.json
+++ b/tests/testthat/_snaps/stack/stack-app-003.json
@@ -39,8 +39,8 @@
 
           ],
           "choices": [
-            "function (data) ",
-            "colnames(data)"
+            "structure(function (data) ",
+            "colnames(data), result = c(\"Time\", \"demand\"))"
           ],
           "multiple": true
         }
diff --git a/tests/testthat/_snaps/stack/stack-app-003_.new.png b/tests/testthat/_snaps/stack/stack-app-003_.new.png
deleted file mode 100644
index b6a99d73..00000000
Binary files a/tests/testthat/_snaps/stack/stack-app-003_.new.png and /dev/null differ
diff --git a/tests/testthat/_snaps/stack/stack-app-003_.png b/tests/testthat/_snaps/stack/stack-app-003_.png
index 173fce55..ce74019b 100644
Binary files a/tests/testthat/_snaps/stack/stack-app-003_.png and b/tests/testthat/_snaps/stack/stack-app-003_.png differ
diff --git a/tests/testthat/_snaps/stack/stack-app-004.json b/tests/testthat/_snaps/stack/stack-app-004.json
index 8819cc6c..af565436 100644
--- a/tests/testthat/_snaps/stack/stack-app-004.json
+++ b/tests/testthat/_snaps/stack/stack-app-004.json
@@ -39,8 +39,8 @@
 
           ],
           "choices": [
-            "function (data) ",
-            "colnames(data)"
+            "structure(function (data) ",
+            "colnames(data), result = c(\"Time\", \"demand\"))"
           ],
           "multiple": true
         }
diff --git a/tests/testthat/_snaps/stack/stack-app-004_.new.png b/tests/testthat/_snaps/stack/stack-app-004_.new.png
deleted file mode 100644
index 3cd83561..00000000
Binary files a/tests/testthat/_snaps/stack/stack-app-004_.new.png and /dev/null differ
diff --git a/tests/testthat/_snaps/stack/stack-app-004_.png b/tests/testthat/_snaps/stack/stack-app-004_.png
index df7d30a3..443e9662 100644
Binary files a/tests/testthat/_snaps/stack/stack-app-004_.png and b/tests/testthat/_snaps/stack/stack-app-004_.png differ
diff --git a/tests/testthat/_snaps/stack/stack-app-005.json b/tests/testthat/_snaps/stack/stack-app-005.json
index 7e62e68f..a70b29a8 100644
--- a/tests/testthat/_snaps/stack/stack-app-005.json
+++ b/tests/testthat/_snaps/stack/stack-app-005.json
@@ -39,8 +39,8 @@
 
           ],
           "choices": [
-            "function (data) ",
-            "colnames(data)"
+            "structure(function (data) ",
+            "colnames(data), result = c(\"Time\", \"demand\"))"
           ],
           "multiple": true
         }
diff --git a/tests/testthat/_snaps/stack/stack-app-005_.new.png b/tests/testthat/_snaps/stack/stack-app-005_.new.png
deleted file mode 100644
index e4785146..00000000
Binary files a/tests/testthat/_snaps/stack/stack-app-005_.new.png and /dev/null differ
diff --git a/tests/testthat/_snaps/stack/stack-app-005_.png b/tests/testthat/_snaps/stack/stack-app-005_.png
index 4f1e88e2..c8ed93db 100644
Binary files a/tests/testthat/_snaps/stack/stack-app-005_.png and b/tests/testthat/_snaps/stack/stack-app-005_.png differ
diff --git a/tests/testthat/_snaps/stack/stack-app-006.json b/tests/testthat/_snaps/stack/stack-app-006.json
index 3952aeb2..2cf11793 100644
--- a/tests/testthat/_snaps/stack/stack-app-006.json
+++ b/tests/testthat/_snaps/stack/stack-app-006.json
@@ -39,8 +39,8 @@
 
           ],
           "choices": [
-            "function (data) ",
-            "colnames(data)"
+            "structure(function (data) ",
+            "colnames(data), result = c(\"Time\", \"demand\"))"
           ],
           "multiple": true
         }
diff --git a/tests/testthat/_snaps/stack/stack-app-006_.new.png b/tests/testthat/_snaps/stack/stack-app-006_.new.png
deleted file mode 100644
index f4b7011e..00000000
Binary files a/tests/testthat/_snaps/stack/stack-app-006_.new.png and /dev/null differ
diff --git a/tests/testthat/_snaps/stack/stack-app-006_.png b/tests/testthat/_snaps/stack/stack-app-006_.png
index 0c362ef4..cd714d6d 100644
Binary files a/tests/testthat/_snaps/stack/stack-app-006_.png and b/tests/testthat/_snaps/stack/stack-app-006_.png differ
diff --git a/tests/testthat/_snaps/stack/stack-app-007.json b/tests/testthat/_snaps/stack/stack-app-007.json
index 5d5eae82..2e06ed50 100644
--- a/tests/testthat/_snaps/stack/stack-app-007.json
+++ b/tests/testthat/_snaps/stack/stack-app-007.json
@@ -39,8 +39,8 @@
 
           ],
           "choices": [
-            "function (data) ",
-            "colnames(data)"
+            "structure(function (data) ",
+            "colnames(data), result = c(\"Time\", \"demand\"))"
           ],
           "multiple": true
         }
diff --git a/tests/testthat/_snaps/stack/stack-app-007_.png b/tests/testthat/_snaps/stack/stack-app-007_.png
index 9e958ce7..475b2e6e 100644
Binary files a/tests/testthat/_snaps/stack/stack-app-007_.png and b/tests/testthat/_snaps/stack/stack-app-007_.png differ
diff --git a/tests/testthat/_snaps/workspace/restore-workspace-app-001_.new.png b/tests/testthat/_snaps/workspace/restore-workspace-app-001_.new.png
index 83cfc7a3..50ee23bb 100644
Binary files a/tests/testthat/_snaps/workspace/restore-workspace-app-001_.new.png and b/tests/testthat/_snaps/workspace/restore-workspace-app-001_.new.png differ
diff --git a/tests/testthat/_snaps/workspace/workspace-app-001_.new.png b/tests/testthat/_snaps/workspace/workspace-app-001_.new.png
index ba1f0729..30df0c07 100644
Binary files a/tests/testthat/_snaps/workspace/workspace-app-001_.new.png and b/tests/testthat/_snaps/workspace/workspace-app-001_.new.png differ
diff --git a/tests/testthat/_snaps/workspace/workspace-app-002_.new.png b/tests/testthat/_snaps/workspace/workspace-app-002_.new.png
index 491126e9..df0a8915 100644
Binary files a/tests/testthat/_snaps/workspace/workspace-app-002_.new.png and b/tests/testthat/_snaps/workspace/workspace-app-002_.new.png differ
diff --git a/tests/testthat/_snaps/workspace/workspace-app-003_.new.png b/tests/testthat/_snaps/workspace/workspace-app-003_.new.png
index 6b69d050..95f66b3c 100644
Binary files a/tests/testthat/_snaps/workspace/workspace-app-003_.new.png and b/tests/testthat/_snaps/workspace/workspace-app-003_.new.png differ
diff --git a/tests/testthat/_snaps/workspace/workspace-app-004_.new.png b/tests/testthat/_snaps/workspace/workspace-app-004_.new.png
index ba1f0729..30df0c07 100644
Binary files a/tests/testthat/_snaps/workspace/workspace-app-004_.new.png and b/tests/testthat/_snaps/workspace/workspace-app-004_.new.png differ
diff --git a/tests/testthat/test-add-block.R b/tests/testthat/test-add-block.R
index 6e790822..f9399abd 100644
--- a/tests/testthat/test-add-block.R
+++ b/tests/testthat/test-add-block.R
@@ -4,16 +4,16 @@ test_that("add_block works", {
 
   stack <- new_stack()
   expect_error(
-    stack |> add_block(new_select_block)
+    stack |> add_block(available_blocks()[["select_block"]])
   )
 
   stack <- new_stack(new_dataset_block) |>
-    add_block(new_select_block)
+    add_block(available_blocks()[["select_block"]])
 
   expect_length(stack, 2)
   expect_s3_class(stack[[2]], "select_block")
 
-  stack <- add_block(stack, new_filter_block, 1)
+  stack <- add_block(stack, available_blocks()[["filter_block"]], 1)
 
   expect_length(stack, 3)
   expect_s3_class(stack[[2]], "filter_block")
diff --git a/tests/testthat/test-registry.R b/tests/testthat/test-registry.R
index 32ded562..2fcf5667 100644
--- a/tests/testthat/test-registry.R
+++ b/tests/testthat/test-registry.R
@@ -68,9 +68,10 @@ test_that("3rd party blocks can be registrerd (script)", {
   }
 
   register_block(
-    new_dummy_block, "Dummy block", "return first n rows",
-    c("dummy_block", "transform_block"), "data.frame", "data.frame",
-    "transform"
+    new_dummy_block,
+    "Dummy block",
+    "return first n rows",
+    category = "transform"
   )
 
   expect_true("dummy_block" %in% list_blocks())
@@ -78,8 +79,7 @@ test_that("3rd party blocks can be registrerd (script)", {
   expect_warning(
     register_block(
       new_dummy_block, "dummy block", "return first n rows",
-      c("dummy_block", "transform_block"), "data.frame", "data.frame",
-      "transform"
+      category = "transform"
     )
   )
 
diff --git a/tests/testthat/test-stack.R b/tests/testthat/test-stack.R
index e730f5db..319efaa9 100644
--- a/tests/testthat/test-stack.R
+++ b/tests/testthat/test-stack.R
@@ -60,19 +60,37 @@ test_that("Get compatible blocks", {
   stack <- new_stack()
   res <- get_compatible_blocks(stack)
   # Might change if we add new data blocks
-  expect_equal(nrow(res), 3)
-  expect_identical(unique(res$category), "data")
+  expect_equal(length(res), 3)
+  expect_identical(unique(chr_ply(res, attr, "category")), "data")
 
   # Uncategorized block
-  attr(block_registry$dataset_block, "category") <- "uncategorized"
+  new_dummy_data_block <- function(...) {
+    new_block(
+      fields = list(),
+      expr = quote(data),
+      class = c("dummy_block", "dataset_block", "data_block"),
+      ...
+    )
+  }
+
+  register_block(
+    new_dummy_data_block,
+    "Dummy block",
+    "return first n rows"
+  )
+
   stack <- new_stack()
   res <- get_compatible_blocks(stack)
-  expect_equal(nrow(res), 3)
-  expect_contains(unique(res$category), c("data", "uncategorized"))
+  expect_equal(length(res), 4)
+  expect_contains(
+    unique(chr_ply(res, attr, "category")),
+    c("data", "uncategorized")
+  )
+  unregister_blocks("dummy_block")
 
   stack <- new_stack(new_dataset_block())
   res <- get_compatible_blocks(stack)
-  expect_identical(unique(res$category), "transform")
+  expect_identical(unique(chr_ply(res, attr, "category")), "transform")
 
   # Check for workspace and result block
   stack1 <- new_stack(
@@ -83,8 +101,8 @@ test_that("Get compatible blocks", {
   stack2 <- new_stack()
 
   set_workspace(stack1 = stack1, stack2 = stack2)
-  expect_true("result_block" %in% get_compatible_blocks(stack2)$ctor)
-  expect_true("result_block" %in% get_compatible_blocks(stack1)$ctor)
+  expect_true("result_block" %in% names(get_compatible_blocks(stack2)))
+  expect_true("result_block" %in% names(get_compatible_blocks(stack1)))
 })
 
 withr::local_package("shinytest2")
diff --git a/tests/testthat/test-validate-block.R b/tests/testthat/test-validate-block.R
index 8513dc8b..1a8ab128 100644
--- a/tests/testthat/test-validate-block.R
+++ b/tests/testthat/test-validate-block.R
@@ -14,7 +14,6 @@ testServer(module_server_test, {
   # Invalidate
   session$setInputs("columns" = "")
   session$flushReact()
-  expect_error(out_dat())
   expect_false(is_valid$block)
   expect_identical(is_valid$message, "selected value(s) not among provided choices")
   expect_identical(is_valid$fields, "columns")
diff --git a/vignettes/blockr-examples.Rmd b/vignettes/blockr-examples.Rmd
index 2162b02c..740f1a92 100644
--- a/vignettes/blockr-examples.Rmd
+++ b/vignettes/blockr-examples.Rmd
@@ -96,7 +96,8 @@ filter_in_block <- function(data, ...) {
         dplyr::filter(!!dplyr::sym(.(column)) %in% vals[[1]])
     }),
     ...,
-    class = c("filter_in_block", "transform_block", "submit_block")
+    class = c("filter_in_block", "transform_block"),
+    submit = NA
   )
 }
 
@@ -104,10 +105,7 @@ blockr::register_block(
   constructor = filter_in_block,
   name = "Filter in",
   description = "Filter on a vector",
-  category = "transform",
-  classes = c("filter_in_block", "transform_block"),
-  input = "data.frame",
-  output = "data.frame"
+  category = "transform"
 )
 ```
 
@@ -168,24 +166,29 @@ new_prophet_forecast_block <- function(columns = character(), ...) {
   )
 }
 
+block_input_check.plot_block <- function(x, data, ...) {
+
+  if (inherits(data, "data.frame")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting data.frame input.")
+}
+
+block_output_ptype.plot_block <- function(x, ...) ggplot()
+
 # Register custom blocks
 register_block(
   new_stock_data_block,
   name = "Stock Data",
   description = "Fetch stock data",
-  category = "data",
-  classes = c("stock_data_block", "data_block"),
-  input = NA_character_,
-  output = "data.frame"
+  category = "data"
 )
 register_block(
   new_prophet_forecast_block,
   name = "Prophet Forecast",
   description = "Forecast using Prophet",
-  category = "plot",
-  classes = c("prophet_forecast_block", "plot_block"),
-  input = "data.frame",
-  output = "plot"
+  category = "plot"
 )
 
 # Create the stack
@@ -282,18 +285,27 @@ new_cardinal02_block <- function(...) {
     expr = expr,
     fields = fields,
     ...,
-    class = c("cardinal02_block", "rtables_block", "submit_block")
+    class = c("cardinal02_block", "rtables_block"),
+    submit = NA
   )
 }
 
+block_input_check.rtables_block <- function(x, data, ...) {
+
+  if (inherits(data, "data.frame")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting data.frame input.")
+}
+
+block_output_ptype.rtables_block <- function(x, ...) list()
+
 register_block(
   new_cardinal02_block,
   "Cardinal 02",
   "A Cardinal 02 table",
-  category = "table",
-  input = "data.frame",
-  output = "list",
-  classes = c("cardinal02_block", "rtables_block", "submit_block")
+  category = "table"
 )
 
 
@@ -380,25 +392,30 @@ new_pollution_forecast_block <- function(columns = character(), ...) {
   )
 }
 
+block_input_check.plot_block <- function(x, data, ...) {
+
+  if (inherits(data, "data.frame")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting data.frame input.")
+}
+
+block_output_ptype.plot_block <- function(x, ...) ggplot()
+
 # Register custom blocks
 register_block(
   new_air_quality_block,
   name = "Air Quality Data",
   description = "Import air quality data",
-  category = "data",
-  classes = c("air_quality_block", "data_block"),
-  input = NA_character_,
-  output = "data.frame"
+  category = "data"
 )
 
 register_block(
   new_pollution_forecast_block,
   name = "Pollution Forecast",
   description = "Forecast pollution levels",
-  category = "plot",
-  classes = c("pollution_forecast_block", "plot_block"),
-  input = "data.frame",
-  output = "plot"
+  category = "plot"
 )
 
 # Create the stack
@@ -560,24 +577,29 @@ new_causal_impact_block <- function(columns = character(), ...) {
   )
 }
 
+block_input_check.plot_block <- function(x, data, ...) {
+
+  if (inherits(data, "data.frame")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting data.frame input.")
+}
+
+block_output_ptype.plot_block <- function(x, ...) ggplot()
+
 # Register custom blocks
 register_block(
   new_marketing_data_block,
   name = "Marketing Data",
   description = "Load and prepare marketing data",
-  category = "data",
-  classes = c("marketing_data_block", "data_block"),
-  input = NA_character_,
-  output = "data.frame"
+  category = "data"
 )
 register_block(
   new_causal_impact_block,
   name = "Causal Impact Analysis",
   description = "Perform Causal Impact analysis on marketing data",
-  category = "plot",
-  classes = c("causal_impact_block", "plot_block"),
-  input = "data.frame",
-  output = "plot"
+  category = "plot"
 )
 
 # Create the stack
diff --git a/vignettes/figures/cmdk-data.png b/vignettes/figures/cmdk-data.png
new file mode 100644
index 00000000..761f325a
Binary files /dev/null and b/vignettes/figures/cmdk-data.png differ
diff --git a/vignettes/figures/cmdk-transform.png b/vignettes/figures/cmdk-transform.png
new file mode 100644
index 00000000..138f5fe2
Binary files /dev/null and b/vignettes/figures/cmdk-transform.png differ
diff --git a/vignettes/plot-block.Rmd b/vignettes/plot-block.Rmd
index 26812058..3d2a515f 100644
--- a/vignettes/plot-block.Rmd
+++ b/vignettes/plot-block.Rmd
@@ -363,6 +363,33 @@ new_geompoint_block <- function(color = character(), shape = character(), ...) {
 
 Note the class `plot_layer_block`. This is necessary to invoke the corresponding `evaluate_block()` method (to use `+` instead of `%>%`).
 
+### Notes about the registry
+
+As mentioned in the __registry__ [vignette](https://bristolmyerssquibb.github.io/blockr/articles/registry.html), to register the newly defined blocks, we have to define 2 methods that check the block __input__ and __output__ (it is no mandatory to register blocks but we highly advise you to do so if you want to benefit from the clever "add block" feature):
+
+```r
+block_input_check.plot_block <- function(x, data, ...) {
+
+  if (inherits(data, "data.frame")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting data.frame input.")
+}
+
+block_output_ptype.plot_block <- function(x, ...) ggplot()
+
+block_input_check.plot_layer_block <- function(x, data, ...) {
+
+  if (inherits(data, "ggplot")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting ggplot input.")
+}
+
+block_output_ptype.plot_layer_block <- function(x, ...) ggplot()
+```
 
 ### Try it
 
diff --git a/vignettes/registry.Rmd b/vignettes/registry.Rmd
index 6ed103f0..a79fd7cb 100644
--- a/vignettes/registry.Rmd
+++ b/vignettes/registry.Rmd
@@ -58,11 +58,13 @@ mermaid("
   blockr_echarts4r --> |register| registry
   subgraph registry[Registry]
     subgraph select_reg[Select block]
+      reg_id[ID: select_block]
       reg_name[Name: select block]
       reg_descr[Description: select columns in a table]
       reg_classes[Classes: select_block, tranform_block]
       reg_input[Input: data.frame]
       reg_output[Output: data.frame]
+      reg_category[Category: Transform blocks]
       reg_package[Package: blockr]
     end
     subgraph filter_reg[Filter block]
@@ -88,42 +90,66 @@ ready to be queried by `available_blocks()`. A truncated output example below:
 
 ```r
 $dataset_block
-function(...) {
-  ...
+function(selected = character(), package = "datasets", ...) {
+  # ... TRUNCATED ... #
 }
 <environment: namespace:blockr>
 attr(,"name")
 [1] "data block"
 attr(,"description")
 [1] "Choose a dataset from a package"
+attr(,"id")
+[1] "dataset_block"
 attr(,"classes")
-[1] "dataset_block" "data_block"   
+[1] "dataset_block" "data_block"    "block"        
 attr(,"input")
-[1] NA
+function(x, data, ...) {
+
+  if (missing(data) || is.null(data)) {
+    return(invisible(NULL))
+  }
+
+  input_failure("No (or empty) input expected.")
+}
+<environment: namespace:blockr>
 attr(,"output")
-[1] "data.frame"
+data frame with 0 columns and 0 rows
 attr(,"package")
 [1] "blockr"
+attr(,"category")
+[1] "data"
 attr(,"class")
 [1] "block_descr"
 
 $select_block
-function(data, ...) {
-  ...
+function(columns = character(), ...) {
+  # ... TRUNCATED ... #
 }
 <environment: namespace:blockr>
 attr(,"name")
 [1] "select block"
 attr(,"description")
 [1] "select columns in a table"
+attr(,"id")
+[1] "select_block"
 attr(,"classes")
-[1] "select_block"    "transform_block"
+[1] "select_block"    "transform_block" "block"          
 attr(,"input")
-[1] "data.frame"
+function(x, data, ...) {
+
+  if (inherits(data, "data.frame")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting data.frame input.")
+}
+<environment: namespace:blockr>
 attr(,"output")
-[1] "data.frame"
+data frame with 0 columns and 0 rows
 attr(,"package")
 [1] "blockr"
+attr(,"category")
+[1] "transform"
 attr(,"class")
 [1] "block_descr"
 ```
@@ -155,15 +181,39 @@ new_tail_block <- function(data, n_rows = numeric(), ...) {
     ...
   )
 }
+```
+
+In addition to that, you also might have to specify what kind of __input__ and __output__ are accepted by that block. We designed 2 helpers, namely `block_input_check()` and `block_output_ptype()`. `{blockr}` already exposes methods like for `dataset_block` and `transform_block` so you don't need to create a new method for those classes. However, we see a practical example on how to create such methods for plots in this [vignette](https://bristolmyerssquibb.github.io/blockr/articles/plot-block.html). Below is what these methods look like, don't forget to export them if you are running inside a R package:
+
+```r
+#' @export
+block_input_check.transform_block <- function(x, data, ...) {
 
+  if (inherits(data, "data.frame")) {
+    return(invisible(NULL))
+  }
+
+  input_failure("Expecting data.frame input.")
+}
+#' @export
+block_output_ptype.transform_block <- function(x, ...) data.frame()
+```
+
+If you forget to create a custom method while it is required, you get an error message as a reminder:
+
+```r
+Error in `UseMethod()`:
+! no applicable method for 'block_output_ptype' applied to an object of class "c('dummy_block', 'data_block', 'block')"
+```
+
+We can now register the new block, as follows:
+
+```{r, eval=TRUE}
 register_block(
   constructor = new_tail_block,
   name = "tail block",
   description = "return last n rows",
-  category = "transform",
-  classes = c("tail_block", "transform_block"),
-  input = "data.frame",
-  output = "data.frame"
+  category = "transform"
 )
 ```
 
@@ -204,14 +254,6 @@ register_blocks(
     "summarize data groups"
   ),
   category = c("data", rep("transform", 3)),
-  classes = list(
-    c("dataset_block", "data_block"),
-    c("filter_block", "transform_block", "submit_block"),
-    c("select_block", "transform_block"),
-    c("summarize_block", "transform_block", "submit_block")
-  ),
-  input = c(NA_character_, "data.frame", "data.frame", "data.frame"),
-  output = c("data.frame", "data.frame", "data.frame", "data.frame"),
   package = "<PKG_NAME>"
 )
 ```
@@ -231,3 +273,109 @@ names(available_blocks())
 where __ids__ is the first entry we applied in the class attributes when the block
 was created, that is `tail_block`. If you had to remove multiple blocks at once,
 you can pass a vector in __ids__.
+
+
+## Leverage the registry API
+
+Having a registry is useful if you want to perform block __compatibility checks__. For instance, we use the registry in the `add_block_server.default` method, responsible for adding a block within a stack. Under the hood, given a stack, `get_compatible_blocks()` is able to return which __registered__ block is compatible with the last stack block, which substantially enhance the user experience:
+
+```{r}
+stack <- new_stack()
+res <- get_compatible_blocks(stack)
+names(res)
+```
+
+If we now add a new `dataset_block` to the stack, the list of suggestion is updated:
+
+```{r}
+stack <- stack |> add_block(available_blocks()[["dataset_block"]])
+res <- get_compatible_blocks(stack)
+names(res)
+```
+
+Within `add_block_server.default`, we update the `shinyWidgets::virtualSelect` choices, being created with `get_compatible_blocks()`. If you wish to develop your own UI, this is totally fine. As an example, we could leverage a contextual menu React widget powered by the [scoutbar](https://www.scoutbar.co/) JS API, those R API is available at [`{scoutbaR}`](https://cynkra.github.io/scoutbaR/). On the UI side, we define the menu placeholder:
+
+```r
+pak::pak("cynkra/scoutbaR")
+
+add_block_ui.custom <- function(x, id, ...) {
+  ns <- shiny::NS(id)
+
+  scoutbaR::scoutbar(
+    ns("scoutbar"),
+    placeholder = c("Click on any block to add it to the current stack")
+  )
+}
+```
+
+On the server side, we update the menu for each new block added to the stack, through `vals$blocks`:
+
+```r
+add_block_server.custom <- function(x, id, vals, ...) {
+  moduleServer(id, function(input, output, session) {
+    ns <- session$ns
+
+    # Triggers on init
+    observeEvent(vals$blocks,
+      {
+        # Pills are dynamically updated from the server
+        # depending on the block compatibility
+        choices <- get_compatible_blocks(vals$stack)
+        cats <- unique(chr_ply(choices, \(b) attr(b, "category")))
+
+        # Create one page per block category
+        choices <- lapply(cats, \(cat) {
+          scoutbaR::scout_section(
+            label = cat,
+            .list = dropNulls(
+              unname(lapply(choices, \(choice) {
+                if (attr(choice, "category") == cat) {
+                  scoutbaR::scout_action(
+                    id = attr(choice, "id"),
+                    label = paste0(attr(choice, "name"), " (", attr(choice, "package"), ")"),
+                    description = attr(choice, "description")
+                  )
+                }
+              })
+            ))
+          )
+        })
+
+        # In this setup, the scoutbar will close after adding a block.
+        # It may be reopened by setting revealScoutbar = TRUE.
+        scoutbaR::update_scoutbar(
+          session,
+          "scoutbar",
+          configuration = list(
+            actions = choices
+          )
+        )
+      }
+    )
+
+    return(
+      list(
+        selected = reactive(input$scoutbar)
+      )
+    )
+  })
+}
+```
+
+Then, we run the stack, passing it a `custom` class so we can benefir from the new defined modules:
+
+```r
+my_stack <- new_stack()
+attr(my_stack, "class") <- c(attr(my_stack, "class"), "custom")
+serve_stack(my_stack)
+```
+
+The contextual menu may be triggered with `cmd + K` on Mac or similar on Windows.
+
+```{r cmdk-empty, echo=FALSE, fig.cap='Scoutbar with empty stack', fig.align = 'center', out.width='50%'}
+knitr::include_graphics("figures/cmdk-data.png")
+```
+
+```{r cmdk-tranform, echo=FALSE, fig.cap='Scoutbar with data block stack', fig.align = 'center', out.width='50%'}
+knitr::include_graphics("figures/cmdk-transform.png")
+```