Index: src/org/openstreetmap/josm/actions/SimplifyWayAction.java
===================================================================
--- src/org/openstreetmap/josm/actions/SimplifyWayAction.java	(revision 18904)
+++ src/org/openstreetmap/josm/actions/SimplifyWayAction.java	(working copy)
@@ -65,6 +65,11 @@
 public class SimplifyWayAction extends JosmAction {
 
     /**
+     * Checkbox for previewing the changes made by the action.
+     */
+    private static JCheckBox preview;
+
+    /**
      * Constructs a new {@code SimplifyWayAction}.
      */
     public SimplifyWayAction() {
@@ -198,6 +203,16 @@
 
         q.setBorder(BorderFactory.createEmptyBorder(14, 0, 10, 0));
         p.add(q, GBC.eol());
+        preview = new JCheckBox(tr("Preview"), true);
+        preview.addActionListener(
+                actionEvent -> {
+                    if (preview.isSelected()) {
+                        l.stateChanged(null);
+                    } else {
+                        changeCleanup.run();
+                    }
+                });
+        p.add(preview, GBC.eol());
         JCheckBox c = new JCheckBox(tr("Do not ask again"));
         p.add(c, GBC.eol());
 
@@ -535,6 +550,9 @@
 
         @Override
         public void stateChanged(ChangeEvent e) {
+            if (preview != null) {
+                preview.setSelected(true);
+            }
             if (Objects.equals(UndoRedoHandler.getInstance().getLastCommand(), lastCommand)) {
                 UndoRedoHandler.getInstance().undo();
             }