diff --git a/lib/livebook/utils.ex b/lib/livebook/utils.ex
index 59d614c66..24a561f0b 100644
--- a/lib/livebook/utils.ex
+++ b/lib/livebook/utils.ex
@@ -174,7 +174,7 @@ defmodule Livebook.Utils do
       if valid_url?(url) do
         []
       else
-        [{:url, "must be a valid URL"}]
+        [{field, "must be a valid URL"}]
       end
     end)
   end
@@ -257,13 +257,16 @@ defmodule Livebook.Utils do
       iex> Livebook.Utils.expand_url("https://example.com/lib/file.ex?token=supersecret", "../root.ex")
       "https://example.com/root.ex?token=supersecret"
 
+      iex> Livebook.Utils.expand_url("https://example.com", "./root.ex")
+      "https://example.com/root.ex"
+
   """
   @spec expand_url(String.t(), String.t()) :: String.t()
   def expand_url(url, relative_path) do
     url
     |> URI.parse()
     |> Map.update!(:path, fn path ->
-      Livebook.FileSystem.Utils.resolve_unix_like_path(path, relative_path)
+      Livebook.FileSystem.Utils.resolve_unix_like_path(path || "/", relative_path)
     end)
     |> URI.to_string()
   end
diff --git a/lib/livebook_web/live/open_live/source_component.ex b/lib/livebook_web/live/open_live/source_component.ex
index f06bb9d86..232379284 100644
--- a/lib/livebook_web/live/open_live/source_component.ex
+++ b/lib/livebook_web/live/open_live/source_component.ex
@@ -1,9 +1,19 @@
 defmodule LivebookWeb.OpenLive.SourceComponent do
   use LivebookWeb, :live_component
 
+  import Ecto.Changeset
+
   @impl true
   def mount(socket) do
-    {:ok, assign(socket, source: "")}
+    {:ok, assign(socket, changeset: changeset())}
+  end
+
+  defp changeset(attrs \\ %{}) do
+    data = %{source: nil}
+    types = %{source: :string}
+
+    cast({data, types}, attrs, [:source])
+    |> validate_required([:source])
   end
 
   @impl true
@@ -16,7 +26,7 @@ defmodule LivebookWeb.OpenLive.SourceComponent do
       </p>
       <.form
         :let={f}
-        for={%{"source" => @source}}
+        for={@changeset}
         as={:data}
         id="import-source"
         phx-submit="import"
@@ -25,7 +35,6 @@ defmodule LivebookWeb.OpenLive.SourceComponent do
         autocomplete="off"
       >
         <.textarea_field
-          type="textarea"
           field={f[:source]}
           label="Notebook source"
           resizable={false}
@@ -34,7 +43,7 @@ defmodule LivebookWeb.OpenLive.SourceComponent do
           spellcheck="false"
           rows="5"
         />
-        <button class="mt-5 button-base button-blue" type="submit" disabled={@source == ""}>
+        <button class="mt-5 button-base button-blue" type="submit" disabled={not @changeset.valid?}>
           Import
         </button>
       </.form>
@@ -43,13 +52,22 @@ defmodule LivebookWeb.OpenLive.SourceComponent do
   end
 
   @impl true
-  def handle_event("validate", %{"data" => %{"source" => source}}, socket) do
-    {:noreply, assign(socket, source: source)}
+  def handle_event("validate", %{"data" => data}, socket) do
+    changeset = data |> changeset() |> Map.replace!(:action, :validate)
+    {:noreply, assign(socket, changeset: changeset)}
   end
 
-  def handle_event("import", %{"data" => %{"source" => source}}, socket) do
-    send(self(), {:import_source, source, []})
+  def handle_event("import", %{"data" => data}, socket) do
+    data
+    |> changeset()
+    |> apply_action(:insert)
+    |> case do
+      {:ok, data} ->
+        send(self(), {:import_source, data.source, []})
+        {:noreply, socket}
 
-    {:noreply, socket}
+      {:error, changeset} ->
+        {:noreply, assign(socket, changeset: changeset)}
+    end
   end
 end
diff --git a/lib/livebook_web/live/open_live/url_component.ex b/lib/livebook_web/live/open_live/url_component.ex
index 4342aaf53..654fcf3a9 100644
--- a/lib/livebook_web/live/open_live/url_component.ex
+++ b/lib/livebook_web/live/open_live/url_component.ex
@@ -1,17 +1,28 @@
 defmodule LivebookWeb.OpenLive.UrlComponent do
   use LivebookWeb, :live_component
 
+  import Ecto.Changeset
+
   alias Livebook.{Utils, Notebook}
 
   @impl true
   def mount(socket) do
-    {:ok, assign(socket, url: "", error_message: nil)}
+    {:ok, assign(socket, changeset: changeset(), error_message: nil)}
+  end
+
+  defp changeset(attrs \\ %{}) do
+    data = %{url: nil}
+    types = %{url: :string}
+
+    cast({data, types}, attrs, [:url])
+    |> validate_required([:url])
+    |> Livebook.Utils.validate_url(:url)
   end
 
   @impl true
   def update(assigns, socket) do
     if url = assigns[:url] do
-      {:ok, do_import(socket, url)}
+      {:ok, do_import(socket, %{url: url})}
     else
       {:ok, socket}
     end
@@ -29,7 +40,7 @@ defmodule LivebookWeb.OpenLive.UrlComponent do
       </p>
       <.form
         :let={f}
-        for={%{"url" => @url}}
+        for={@changeset}
         as={:data}
         phx-submit="import"
         phx-change="validate"
@@ -43,11 +54,7 @@ defmodule LivebookWeb.OpenLive.UrlComponent do
           aria-labelledby="import-from-url"
           spellcheck="false"
         />
-        <button
-          class="mt-5 button-base button-blue"
-          type="submit"
-          disabled={not Utils.valid_url?(@url)}
-        >
+        <button class="mt-5 button-base button-blue" type="submit" disabled={not @changeset.valid?}>
           Import
         </button>
       </.form>
@@ -56,27 +63,41 @@ defmodule LivebookWeb.OpenLive.UrlComponent do
   end
 
   @impl true
-  def handle_event("validate", %{"data" => %{"url" => url}}, socket) do
-    {:noreply, assign(socket, url: url)}
+  def handle_event("validate", %{"data" => data}, socket) do
+    changeset = data |> changeset() |> Map.replace!(:action, :validate)
+    {:noreply, assign(socket, changeset: changeset)}
   end
 
-  def handle_event("import", %{"data" => %{"url" => url}}, socket) do
-    {:noreply, do_import(socket, url)}
+  def handle_event("import", %{"data" => data}, socket) do
+    {:noreply, do_import(socket, data)}
   end
 
-  defp do_import(socket, url) do
-    origin = Notebook.ContentLoader.url_to_location(url)
-    files_url = Livebook.Utils.expand_url(url, "files/")
-
-    origin
-    |> Notebook.ContentLoader.fetch_content_from_location()
+  defp do_import(socket, data) do
+    data
+    |> changeset()
+    |> apply_action(:insert)
     |> case do
-      {:ok, content} ->
-        send(self(), {:import_source, content, [origin: origin, files_source: {:url, files_url}]})
-        socket
+      {:ok, data} ->
+        origin = Notebook.ContentLoader.url_to_location(data.url)
+        files_url = Livebook.Utils.expand_url(data.url, "files/")
 
-      {:error, message} ->
-        assign(socket, url: url, error_message: Utils.upcase_first(message))
+        origin
+        |> Notebook.ContentLoader.fetch_content_from_location()
+        |> case do
+          {:ok, content} ->
+            opts = [origin: origin, files_source: {:url, files_url}]
+            send(self(), {:import_source, content, opts})
+            socket
+
+          {:error, message} ->
+            assign(socket,
+              changeset: changeset(data),
+              error_message: Utils.upcase_first(message)
+            )
+        end
+
+      {:error, changeset} ->
+        assign(socket, changeset: changeset)
     end
   end
 end
diff --git a/lib/livebook_web/live/session_live/attached_live.ex b/lib/livebook_web/live/session_live/attached_live.ex
index b58c13364..3756fd60b 100644
--- a/lib/livebook_web/live/session_live/attached_live.ex
+++ b/lib/livebook_web/live/session_live/attached_live.ex
@@ -1,6 +1,8 @@
 defmodule LivebookWeb.SessionLive.AttachedLive do
   use LivebookWeb, :live_view
 
+  import Ecto.Changeset
+
   alias Livebook.{Session, Runtime}
 
   @impl true
@@ -24,10 +26,26 @@ defmodule LivebookWeb.SessionLive.AttachedLive do
        session: session,
        current_runtime: current_runtime,
        error_message: nil,
-       data: initial_data(current_runtime)
+       changeset: changeset(current_runtime)
      )}
   end
 
+  defp changeset(runtime, attrs \\ %{}) do
+    data =
+      case runtime do
+        %Runtime.Attached{node: node, cookie: cookie} ->
+          %{name: Atom.to_string(node), cookie: Atom.to_string(cookie)}
+
+        _ ->
+          %{name: nil, cookie: nil}
+      end
+
+    types = %{name: :string, cookie: :string}
+
+    cast({data, types}, attrs, [:name, :cookie])
+    |> validate_required([:name, :cookie])
+  end
+
   @impl true
   def render(assigns) do
     ~H"""
@@ -53,7 +71,7 @@ defmodule LivebookWeb.SessionLive.AttachedLive do
       </p>
       <.form
         :let={f}
-        for={@data}
+        for={@changeset}
         as={:data}
         phx-submit="init"
         phx-change="validate"
@@ -64,42 +82,48 @@ defmodule LivebookWeb.SessionLive.AttachedLive do
           <.text_field field={f[:name]} label="Name" placeholder={name_placeholder()} />
           <.text_field field={f[:cookie]} label="Cookie" placeholder="mycookie" />
         </div>
-        <button class="mt-5 button-base button-blue" type="submit" disabled={not data_valid?(@data)}>
-          <%= if(matching_runtime?(@current_runtime, @data), do: "Reconnect", else: "Connect") %>
+        <button class="mt-5 button-base button-blue" type="submit" disabled={not @changeset.valid?}>
+          <%= if(reconnecting?(@changeset), do: "Reconnect", else: "Connect") %>
         </button>
       </.form>
     </div>
     """
   end
 
-  defp matching_runtime?(%Runtime.Attached{} = runtime, data) do
-    initial_data(runtime) == data
-  end
-
-  defp matching_runtime?(_runtime, _data), do: false
-
   @impl true
   def handle_event("validate", %{"data" => data}, socket) do
-    {:noreply, assign(socket, data: data)}
+    changeset =
+      socket.assigns.current_runtime |> changeset(data) |> Map.replace!(:action, :validate)
+
+    {:noreply, assign(socket, changeset: changeset)}
   end
 
   def handle_event("init", %{"data" => data}, socket) do
-    node = String.to_atom(data["name"])
-    cookie = String.to_atom(data["cookie"])
+    socket.assigns.current_runtime
+    |> changeset(data)
+    |> apply_action(:insert)
+    |> case do
+      {:ok, data} ->
+        node = String.to_atom(data.name)
+        cookie = String.to_atom(data.cookie)
 
-    runtime = Runtime.Attached.new(node, cookie)
+        runtime = Runtime.Attached.new(node, cookie)
 
-    case Runtime.connect(runtime) do
-      {:ok, runtime} ->
-        Session.set_runtime(socket.assigns.session.pid, runtime)
-        {:noreply, assign(socket, data: initial_data(runtime), error_message: nil)}
+        case Runtime.connect(runtime) do
+          {:ok, runtime} ->
+            Session.set_runtime(socket.assigns.session.pid, runtime)
+            {:noreply, assign(socket, changeset: changeset(runtime), error_message: nil)}
 
-      {:error, message} ->
-        {:noreply,
-         assign(socket,
-           data: data,
-           error_message: Livebook.Utils.upcase_first(message)
-         )}
+          {:error, message} ->
+            {:noreply,
+             assign(socket,
+               changeset: changeset(socket.assigns.current_runtime, data),
+               error_message: Livebook.Utils.upcase_first(message)
+             )}
+        end
+
+      {:error, changeset} ->
+        {:noreply, assign(socket, changeset: changeset)}
     end
   end
 
@@ -110,17 +134,8 @@ defmodule LivebookWeb.SessionLive.AttachedLive do
 
   def handle_info(_message, socket), do: {:noreply, socket}
 
-  defp initial_data(%Runtime.Attached{node: node, cookie: cookie}) do
-    %{
-      "name" => Atom.to_string(node),
-      "cookie" => Atom.to_string(cookie)
-    }
-  end
-
-  defp initial_data(_runtime), do: %{"name" => "", "cookie" => ""}
-
-  defp data_valid?(data) do
-    data["name"] != "" and data["cookie"] != ""
+  defp reconnecting?(changeset) do
+    changeset.valid? and changeset.data == apply_changes(changeset)
   end
 
   defp name_placeholder do
diff --git a/lib/livebook_web/live/settings_live/add_file_system_component.ex b/lib/livebook_web/live/settings_live/add_file_system_component.ex
index 955f751ea..df4d5c09a 100644
--- a/lib/livebook_web/live/settings_live/add_file_system_component.ex
+++ b/lib/livebook_web/live/settings_live/add_file_system_component.ex
@@ -1,11 +1,28 @@
 defmodule LivebookWeb.SettingsLive.AddFileSystemComponent do
   use LivebookWeb, :live_component
 
+  import Ecto.Changeset
+
   alias Livebook.FileSystem
 
   @impl true
   def mount(socket) do
-    {:ok, assign(socket, data: empty_data(), error_message: nil)}
+    {:ok, assign(socket, changeset: changeset(), error_message: nil)}
+  end
+
+  defp changeset(attrs \\ %{}) do
+    data = %{bucket_url: nil, region: nil, access_key_id: nil, secret_access_key: nil}
+
+    types = %{
+      bucket_url: :string,
+      region: :string,
+      access_key_id: :string,
+      secret_access_key: :string
+    }
+
+    cast({data, types}, attrs, [:bucket_url, :region, :access_key_id, :secret_access_key])
+    |> validate_required([:bucket_url, :access_key_id, :secret_access_key])
+    |> Livebook.Utils.validate_url(:bucket_url)
   end
 
   @impl true
@@ -25,7 +42,7 @@ defmodule LivebookWeb.SettingsLive.AddFileSystemComponent do
       </div>
       <.form
         :let={f}
-        for={@data}
+        for={@changeset}
         as={:data}
         phx-target={@myself}
         phx-submit="add"
@@ -43,7 +60,7 @@ defmodule LivebookWeb.SettingsLive.AddFileSystemComponent do
           <.password_field field={f[:access_key_id]} label="Access Key ID" />
           <.password_field field={f[:secret_access_key]} label="Access Key ID" />
           <div class="flex space-x-2">
-            <button class="button-base button-blue" type="submit" disabled={not data_valid?(@data)}>
+            <button class="button-base button-blue" type="submit" disabled={not @changeset.valid?}>
               Add
             </button>
             <.link patch={@return_to} class="button-base button-outlined-gray">
@@ -58,38 +75,39 @@ defmodule LivebookWeb.SettingsLive.AddFileSystemComponent do
 
   @impl true
   def handle_event("validate", %{"data" => data}, socket) do
-    {:noreply, assign(socket, :data, data)}
+    changeset = data |> changeset() |> Map.replace!(:action, :validate)
+    {:noreply, assign(socket, changeset: changeset)}
   end
 
   def handle_event("add", %{"data" => data}, socket) do
-    file_system = data_to_file_system(data)
-    default_dir = FileSystem.File.new(file_system)
+    data
+    |> changeset()
+    |> apply_action(:insert)
+    |> case do
+      {:ok, data} ->
+        file_system =
+          FileSystem.S3.new(data.bucket_url, data.access_key_id, data.secret_access_key,
+            region: data.region
+          )
 
-    case FileSystem.File.list(default_dir) do
-      {:ok, _} ->
-        Livebook.Settings.save_file_system(file_system)
-        send(self(), {:file_systems_updated, Livebook.Settings.file_systems()})
-        {:noreply, push_patch(socket, to: socket.assigns.return_to)}
+        default_dir = FileSystem.File.new(file_system)
 
-      {:error, message} ->
-        {:noreply, assign(socket, error_message: "Connection test failed: " <> message)}
+        case FileSystem.File.list(default_dir) do
+          {:ok, _} ->
+            Livebook.Settings.save_file_system(file_system)
+            send(self(), {:file_systems_updated, Livebook.Settings.file_systems()})
+            {:noreply, push_patch(socket, to: socket.assigns.return_to)}
+
+          {:error, message} ->
+            {:noreply,
+             assign(socket,
+               changeset: changeset(data),
+               error_message: "Connection test failed: " <> message
+             )}
+        end
+
+      {:error, changeset} ->
+        {:noreply, assign(socket, changeset: changeset)}
     end
   end
-
-  defp empty_data() do
-    %{"bucket_url" => "", "region" => "", "access_key_id" => "", "secret_access_key" => ""}
-  end
-
-  defp data_valid?(data) do
-    Livebook.Utils.valid_url?(data["bucket_url"]) and data["access_key_id"] != "" and
-      data["secret_access_key"] != ""
-  end
-
-  defp data_to_file_system(data) do
-    region = if(data["region"] != "", do: data["region"])
-
-    FileSystem.S3.new(data["bucket_url"], data["access_key_id"], data["secret_access_key"],
-      region: region
-    )
-  end
 end