diff --git a/inventory/templates/testing.html b/inventory/templates/testing.html
index 1a23a81..5272505 100644
--- a/inventory/templates/testing.html
+++ b/inventory/templates/testing.html
@@ -205,6 +205,9 @@ const toolBarEl = document.getElementById('toolBar');
 const fillOpacityEl = document.getElementById('fillOpacity');
 
 let doc = loadDoc();
+let shapes = sanitizeShapes(Array.isArray(doc.shapes) ? doc.shapes : []);
+saveDoc({ ...doc, shapes });
+
 let cellSize = Number(doc.cellSize) || 25;
 cellSizeEl.value = cellSize;
 let dotSize = Math.floor(Math.max(cellSize * 1.25, 32));
@@ -212,10 +215,11 @@ let dotSize = Math.floor(Math.max(cellSize * 1.25, 32));
 let ctx;
 let dpr = 1;
 let selectedColor;
-let currentOpacity = clamp01(fillOpacity?.value ?? 0.15, 0.15);
+let currentOpacity = clamp01(fillOpacityEl?.value ?? 0.15, 0.15);
 
 let currentShape = null;
-let shapes = Array.isArray(doc.shapes) ? doc.shapes : [];
+const history = [structuredClone(shapes)];
+let historyIndex = 0
 
 let sizingRAF = 0;
 let lastApplied = { w: 0, h: 0 };
@@ -234,11 +238,36 @@ if (savedType) {
 }
 
 resizeAndSetupCanvas();
-window.addEventListener('resize', resizeAndSetupCanvas);
 
 setGrid();
 scheduleSnappedcellSize();
 
+function undo() {
+    if (historyIndex <= 0) return;
+    historyIndex--;
+    shapes = structuredClone(history[historyIndex]);
+    saveDoc({ ...doc, shapes, cellSize });
+    redrawAll();
+}
+
+function redo() {
+    if (historyIndex >= history.length - 1) return;
+    historyIndex++;
+    shapes = structuredClone(history[historyIndex]);
+    saveDoc({ ...doc, shapes, cellSize });
+    redrawAll();
+}
+
+function commit(nextShapes) {
+    history.splice(historyIndex + 1);
+    history.push(structuredClone(nextShapes));
+    historyIndex++;
+    shapes = nextShapes;
+
+    saveDoc({ ...doc, shapes, cellSize });
+    redrawAll();
+}
+
 function clamp01(n, fallback = 0.15) {
     const x = Number(n);
     return Number.isFinite(x) ? Math.min(1, Math.max(0, x)) : fallback;
@@ -247,23 +276,27 @@ function clamp01(n, fallback = 0.15) {
 function isFiniteNum(n) { return Number.isFinite(Number(n)); }
 
 function sanitizeShapes(list) {
-    const allowed = ['rect', 'ellipse', 'line'];
+  const allowed = new Set(['rect','ellipse','line']);
 
-    return list.filter(s => {
-        if (!s || typeof s !== 'object') return false;
-        if (!allowed.includes(s.type)) return false;
+  return list.flatMap((s) => {
+    if (!s || typeof s !== 'object' || !allowed.has(s.type)) return [];
+    const color = typeof s.color === 'string' ? s.color : '#000000';
+    const opacity = clamp01(s.opacity, 0.15);
 
-        if (!s.color) s.color = '#000000';
+    if (s.type === 'line') {
+      if (!['x1','y1','x2','y2'].every(k => isFiniteNum(s[k]))) return [];
+      return [{ type:'line', x1:+s.x1, y1:+s.y1, x2:+s.x2, y2:+s.y2, color }];
+    }
 
-        if (s.opacity == null) s.opacity = 0.15;
-        s.opacity = clamp01(s.opacity, 0.15);
-
-        if (s.type === 'line') {
-            return ['x1','y1','x2','y2'].every(k => isFiniteNum(s[k]));
-        } else {
-            return ['x','y','w','h'].every(k => isFiniteNum(s[k]));
-        }
-    });
+    if (!['x','y','w','h'].every(k => isFiniteNum(s[k]))) return [];
+    return [{
+      type: s.type,
+      x:+s.x, y:+s.y, w:+s.w, h:+s.h,
+      color,
+      fill: !!s.fill,
+      opacity
+    }];
+  });
 }
 
 function loadDoc() {
@@ -382,11 +415,11 @@ function snapToGrid(x, y) {
     let snapY = localY;
 
     if (type === 'fullGrid' || type === 'verticalGrid') {
-        snapX = ix * grid;
+        snapX = Math.min(ix * grid, rect.width);
     }
 
     if (type === 'fullGrid' || type === 'horizontalGrid') {
-        snapY = iy * grid;
+        snapY = Math.min(iy * grid, rect.height);
     }
 
     return {
@@ -637,11 +670,9 @@ exportEl.addEventListener('click', () => {
 
 clearEl.addEventListener('click', () => {
     cellSize = 25;
-    shapes = [];
-    saveDoc({...doc, shapes, cellSize});
     cellSizeEl.value = 25;
     applycellSize(25);
-    redrawAll();
+    commit([]);
 });
 
 colorEl.addEventListener('input', () => {
@@ -657,11 +688,11 @@ document.addEventListener('keydown', (e) => {
 
     if ((e.ctrlKey || e.metaKey) && key === 'z') {
         e.preventDefault();
-        if (shapes.length > 0) {
-            shapes.pop();
-            saveDoc({ ...doc, shapes, cellSize });
-            redrawAll();
-        }
+        undo();
+    }
+
+    if ((e.ctrlKey || e.metaKey) && (key === 'y' || (e.shiftKey && key === 'z'))) {
+        e.preventDefault(); redo();
     }
 
     if (key === 'escape' && currentShape) {
@@ -833,10 +864,7 @@ window.addEventListener('pointerup', (e) => {
         if (ellipse.w > 0 && ellipse.h > 0) finalShape = ellipse;
     }
 
-    if (finalShape) {
-        shapes.push(finalShape);
-        saveDoc({...doc, shapes, cellSize});
-    }
+    if (finalShape) commit([...shapes, finalShape]);
 
     clearCanvas();
     shapes.forEach(drawShape);