diff --git a/.eslintignore b/.eslintignore
index 35534fa3..388ef910 100644
--- a/.eslintignore
+++ b/.eslintignore
@@ -11,5 +11,5 @@ CHECKS
 docker-compose.yml
 Dockerfile
 LICENSE
-nightwatch.config.js
+nightwatch.conf.js
 README.md
diff --git a/.eslintrc.js b/.eslintrc.js
index 346e1cbe..94e6f083 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -25,5 +25,6 @@ module.exports = {
   },
   rules: {
     "no-prototype-builtins": "off",
+    "no-undef": "warn",
   },
 };
diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 20e415ce..19e3d026 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -41,3 +41,17 @@ jobs:
 
       - name: Run Prettier check
         run: npx prettier --check .
+
+  
+  lint:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Install dependencies
+        run: npm install
+
+      - name: Run ESLint
+        run: npx eslint .
diff --git a/client-data/js/board.js b/client-data/js/board.js
index 2d8c900d..85493f56 100644
--- a/client-data/js/board.js
+++ b/client-data/js/board.js
@@ -23,7 +23,7 @@
  *
  * @licend
  */
-
+const Minitpl = require('./minitpl')
 var Tools = {};
 
 Tools.i18n = (function i18n() {
@@ -75,6 +75,7 @@ Tools.connect = function () {
     socket_params.query = "token=" + params.get("token");
   }
 
+  // eslint-disable-next-line no-undef
   this.socket = io.connect("", socket_params);
 
   //Receive draw instructions from the server
@@ -588,6 +589,7 @@ Tools.toolHooks = [
       };
     }
 
+    // eslint-disable-next-line no-unused-vars
     function wrapUnsetHover(f, toolName) {
       return function unsetHover(evt) {
         document.activeElement &&
@@ -643,6 +645,7 @@ Tools.generateUID = function (prefix, suffix) {
 Tools.createSVGElement = function createSVGElement(name, attrs) {
   var elem = document.createElementNS(Tools.svg.namespaceURI, name);
   if (typeof attrs !== "object") return elem;
+  // eslint-disable-next-line no-unused-vars
   Object.keys(attrs).forEach(function (key, i) {
     elem.setAttributeNS(null, key, attrs[key]);
   });
@@ -764,6 +767,7 @@ Tools.svg.height.baseVal.value = document.body.clientHeight;
     var dy = evt.clientY - pos.scroll;
     menu.scrollTop = pos.top - dy;
   }
+  // eslint-disable-next-line no-unused-vars
   function menu_mouseup(evt) {
     menu.removeEventListener("mousemove", menu_mousemove);
     document.removeEventListener("mouseup", menu_mouseup);
diff --git a/client-data/js/canvascolor.js b/client-data/js/canvascolor.js
index a3ccbd85..272047ce 100644
--- a/client-data/js/canvascolor.js
+++ b/client-data/js/canvascolor.js
@@ -34,6 +34,7 @@
 // @use_types_for_optimization true
 // ==/ClosureCompiler==
 
+// eslint-disable-next-line no-unused-vars
 var canvascolor = (function () {
   //Code Isolation
   "use strict";
diff --git a/client-data/js/minitpl.js b/client-data/js/minitpl.js
index 0a32af9c..ca54182a 100644
--- a/client-data/js/minitpl.js
+++ b/client-data/js/minitpl.js
@@ -23,8 +23,9 @@
  *
  * @licend
  */
-
-Minitpl = (function () {
+// eslint-disable-next-line no-unused-vars
+const Minitpl = (function () {
+  // eslint-disable-next-line no-unused-vars
   function Minitpl(elem, data) {
     this.elem = typeof elem === "string" ? document.querySelector(elem) : elem;
     if (!elem) {
diff --git a/client-data/js/path-data-polyfill.js b/client-data/js/path-data-polyfill.js
index fd38dff7..cebd09b9 100644
--- a/client-data/js/path-data-polyfill.js
+++ b/client-data/js/path-data-polyfill.js
@@ -539,8 +539,8 @@ if (
         var curves = [];
 
         for (var i = 0; i < params.length; i += 3) {
-          var r1 = rotate(params[i][0], params[i][1], angleRad);
-          var r2 = rotate(params[i + 1][0], params[i + 1][1], angleRad);
+          r1 = rotate(params[i][0], params[i][1], angleRad);
+          r2 = rotate(params[i + 1][0], params[i + 1][1], angleRad);
           var r3 = rotate(params[i + 2][0], params[i + 2][1], angleRad);
           curves.push([r1.x, r1.y, r2.x, r2.y, r3.x, r3.y]);
         }
@@ -584,8 +584,8 @@ if (
           currentX = x;
           currentY = y;
         } else if (type === "m") {
-          var x = currentX + seg.values[0];
-          var y = currentY + seg.values[1];
+          x = currentX + seg.values[0];
+          y = currentY + seg.values[1];
 
           absolutizedPathData.push({ type: "M", values: [x, y] });
 
@@ -595,16 +595,16 @@ if (
           currentX = x;
           currentY = y;
         } else if (type === "L") {
-          var x = seg.values[0];
-          var y = seg.values[1];
+          x = seg.values[0];
+          y = seg.values[1];
 
           absolutizedPathData.push({ type: "L", values: [x, y] });
 
           currentX = x;
           currentY = y;
         } else if (type === "l") {
-          var x = currentX + seg.values[0];
-          var y = currentY + seg.values[1];
+          x = currentX + seg.values[0];
+          y = currentY + seg.values[1];
 
           absolutizedPathData.push({ type: "L", values: [x, y] });
 
@@ -615,8 +615,8 @@ if (
           var y1 = seg.values[1];
           var x2 = seg.values[2];
           var y2 = seg.values[3];
-          var x = seg.values[4];
-          var y = seg.values[5];
+          x = seg.values[4];
+          y = seg.values[5];
 
           absolutizedPathData.push({
             type: "C",
@@ -626,12 +626,12 @@ if (
           currentX = x;
           currentY = y;
         } else if (type === "c") {
-          var x1 = currentX + seg.values[0];
-          var y1 = currentY + seg.values[1];
-          var x2 = currentX + seg.values[2];
-          var y2 = currentY + seg.values[3];
-          var x = currentX + seg.values[4];
-          var y = currentY + seg.values[5];
+          x1 = currentX + seg.values[0];
+          y1 = currentY + seg.values[1];
+          x2 = currentX + seg.values[2];
+          y2 = currentY + seg.values[3];
+          x = currentX + seg.values[4];
+          y = currentY + seg.values[5];
 
           absolutizedPathData.push({
             type: "C",
@@ -641,28 +641,28 @@ if (
           currentX = x;
           currentY = y;
         } else if (type === "Q") {
-          var x1 = seg.values[0];
-          var y1 = seg.values[1];
-          var x = seg.values[2];
-          var y = seg.values[3];
+          x1 = seg.values[0];
+          y1 = seg.values[1];
+          x = seg.values[2];
+          y = seg.values[3];
 
           absolutizedPathData.push({ type: "Q", values: [x1, y1, x, y] });
 
           currentX = x;
           currentY = y;
         } else if (type === "q") {
-          var x1 = currentX + seg.values[0];
-          var y1 = currentY + seg.values[1];
-          var x = currentX + seg.values[2];
-          var y = currentY + seg.values[3];
+          x1 = currentX + seg.values[0];
+          y1 = currentY + seg.values[1];
+          x = currentX + seg.values[2];
+          y = currentY + seg.values[3];
 
           absolutizedPathData.push({ type: "Q", values: [x1, y1, x, y] });
 
           currentX = x;
           currentY = y;
         } else if (type === "A") {
-          var x = seg.values[5];
-          var y = seg.values[6];
+          x = seg.values[5];
+          y = seg.values[6];
 
           absolutizedPathData.push({
             type: "A",
@@ -680,8 +680,8 @@ if (
           currentX = x;
           currentY = y;
         } else if (type === "a") {
-          var x = currentX + seg.values[5];
-          var y = currentY + seg.values[6];
+          x = currentX + seg.values[5];
+          y = currentY + seg.values[6];
 
           absolutizedPathData.push({
             type: "A",
@@ -699,52 +699,52 @@ if (
           currentX = x;
           currentY = y;
         } else if (type === "H") {
-          var x = seg.values[0];
+          x = seg.values[0];
           absolutizedPathData.push({ type: "H", values: [x] });
           currentX = x;
         } else if (type === "h") {
-          var x = currentX + seg.values[0];
+          x = currentX + seg.values[0];
           absolutizedPathData.push({ type: "H", values: [x] });
           currentX = x;
         } else if (type === "V") {
-          var y = seg.values[0];
+          y = seg.values[0];
           absolutizedPathData.push({ type: "V", values: [y] });
           currentY = y;
         } else if (type === "v") {
-          var y = currentY + seg.values[0];
+          y = currentY + seg.values[0];
           absolutizedPathData.push({ type: "V", values: [y] });
           currentY = y;
         } else if (type === "S") {
-          var x2 = seg.values[0];
-          var y2 = seg.values[1];
-          var x = seg.values[2];
-          var y = seg.values[3];
+          x2 = seg.values[0];
+          y2 = seg.values[1];
+          x = seg.values[2];
+          y = seg.values[3];
 
           absolutizedPathData.push({ type: "S", values: [x2, y2, x, y] });
 
           currentX = x;
           currentY = y;
         } else if (type === "s") {
-          var x2 = currentX + seg.values[0];
-          var y2 = currentY + seg.values[1];
-          var x = currentX + seg.values[2];
-          var y = currentY + seg.values[3];
+          x2 = currentX + seg.values[0];
+          y2 = currentY + seg.values[1];
+          x = currentX + seg.values[2];
+          y = currentY + seg.values[3];
 
           absolutizedPathData.push({ type: "S", values: [x2, y2, x, y] });
 
           currentX = x;
           currentY = y;
         } else if (type === "T") {
-          var x = seg.values[0];
-          var y = seg.values[1];
+          x = seg.values[0];
+          y = seg.values[1];
 
           absolutizedPathData.push({ type: "T", values: [x, y] });
 
           currentX = x;
           currentY = y;
         } else if (type === "t") {
-          var x = currentX + seg.values[0];
-          var y = currentY + seg.values[1];
+          x = currentX + seg.values[0];
+          y = currentY + seg.values[1];
 
           absolutizedPathData.push({ type: "T", values: [x, y] });
 
@@ -794,8 +794,8 @@ if (
           var y1 = seg.values[1];
           var x2 = seg.values[2];
           var y2 = seg.values[3];
-          var x = seg.values[4];
-          var y = seg.values[5];
+          x = seg.values[4];
+          y = seg.values[5];
 
           reducedPathData.push({ type: "C", values: [x1, y1, x2, y2, x, y] });
 
@@ -805,30 +805,30 @@ if (
           currentX = x;
           currentY = y;
         } else if (seg.type === "L") {
-          var x = seg.values[0];
-          var y = seg.values[1];
+          x = seg.values[0];
+          y = seg.values[1];
 
           reducedPathData.push({ type: "L", values: [x, y] });
 
           currentX = x;
           currentY = y;
         } else if (seg.type === "H") {
-          var x = seg.values[0];
+          x = seg.values[0];
 
           reducedPathData.push({ type: "L", values: [x, currentY] });
 
           currentX = x;
         } else if (seg.type === "V") {
-          var y = seg.values[0];
+          y = seg.values[0];
 
           reducedPathData.push({ type: "L", values: [currentX, y] });
 
           currentY = y;
         } else if (seg.type === "S") {
-          var x2 = seg.values[0];
-          var y2 = seg.values[1];
-          var x = seg.values[2];
-          var y = seg.values[3];
+          x2 = seg.values[0];
+          y2 = seg.values[1];
+          x = seg.values[2];
+          y = seg.values[3];
 
           var cx1, cy1;
 
@@ -848,10 +848,10 @@ if (
           currentX = x;
           currentY = y;
         } else if (seg.type === "T") {
-          var x = seg.values[0];
-          var y = seg.values[1];
+          x = seg.values[0];
+          y = seg.values[1];
 
-          var x1, y1;
+          // var x1, y1;
 
           if (lastType === "Q" || lastType === "T") {
             x1 = currentX + (currentX - lastControlX);
@@ -861,8 +861,8 @@ if (
             y1 = currentY;
           }
 
-          var cx1 = currentX + (2 * (x1 - currentX)) / 3;
-          var cy1 = currentY + (2 * (y1 - currentY)) / 3;
+          cx1 = currentX + (2 * (x1 - currentX)) / 3;
+          cy1 = currentY + (2 * (y1 - currentY)) / 3;
           var cx2 = x + (2 * (x1 - x)) / 3;
           var cy2 = y + (2 * (y1 - y)) / 3;
 
@@ -877,15 +877,15 @@ if (
           currentX = x;
           currentY = y;
         } else if (seg.type === "Q") {
-          var x1 = seg.values[0];
-          var y1 = seg.values[1];
-          var x = seg.values[2];
-          var y = seg.values[3];
+          x1 = seg.values[0];
+          y1 = seg.values[1];
+          x = seg.values[2];
+          y = seg.values[3];
 
-          var cx1 = currentX + (2 * (x1 - currentX)) / 3;
-          var cy1 = currentY + (2 * (y1 - currentY)) / 3;
-          var cx2 = x + (2 * (x1 - x)) / 3;
-          var cy2 = y + (2 * (y1 - y)) / 3;
+          cx1 = currentX + (2 * (x1 - currentX)) / 3;
+          cy1 = currentY + (2 * (y1 - currentY)) / 3;
+          cx2 = x + (2 * (x1 - x)) / 3;
+          cy2 = y + (2 * (y1 - y)) / 3;
 
           reducedPathData.push({
             type: "C",
@@ -903,8 +903,8 @@ if (
           var angle = seg.values[2];
           var largeArcFlag = seg.values[3];
           var sweepFlag = seg.values[4];
-          var x = seg.values[5];
-          var y = seg.values[6];
+          x = seg.values[5];
+          y = seg.values[6];
 
           if (r1 === 0 || r2 === 0) {
             reducedPathData.push({
@@ -958,6 +958,7 @@ if (
       setAttribute.call(this, name, value);
     };
 
+    // eslint-disable-next-line no-unused-vars
     SVGPathElement.prototype.removeAttribute = function (name, value) {
       if (name === "d") {
         this[$cachedPathData] = null;
@@ -989,7 +990,7 @@ if (
         if (this[$cachedPathData]) {
           return clonePathData(this[$cachedPathData]);
         } else {
-          var pathData = parsePathDataString(this.getAttribute("d") || "");
+          pathData = parsePathDataString(this.getAttribute("d") || "");
           this[$cachedPathData] = clonePathData(pathData);
           return pathData;
         }
diff --git a/client-data/tools/clear/clear.js b/client-data/tools/clear/clear.js
index 29c01118..dd7b2c22 100644
--- a/client-data/tools/clear/clear.js
+++ b/client-data/tools/clear/clear.js
@@ -36,6 +36,7 @@
     Tools.drawAndSend(msg, Tools.list["Clear"]);
   }
 
+  // eslint-disable-next-line no-unused-vars
   function draw(data) {
     Tools.drawingArea.innerHTML = "";
   }
diff --git a/client-data/tools/ellipse/ellipse.js b/client-data/tools/ellipse/ellipse.js
index 1450fac1..33f64280 100644
--- a/client-data/tools/ellipse/ellipse.js
+++ b/client-data/tools/ellipse/ellipse.js
@@ -56,6 +56,7 @@
       y2: y,
     });
 
+    // eslint-disable-next-line no-self-assign
     curUpdate.id = curUpdate.id;
     curUpdate.x = x;
     curUpdate.y = y;
diff --git a/client-data/tools/grid/grid.js b/client-data/tools/grid/grid.js
index be6885d3..f688ddfe 100644
--- a/client-data/tools/grid/grid.js
+++ b/client-data/tools/grid/grid.js
@@ -30,6 +30,7 @@
   var index = 0; //grid off by default
   var states = ["none", "url(#grid)", "url(#dots)"];
 
+  // eslint-disable-next-line no-unused-vars
   function toggleGrid(evt) {
     index = (index + 1) % states.length;
     gridContainer.setAttributeNS(null, "fill", states[index]);
diff --git a/client-data/tools/hand/hand.js b/client-data/tools/hand/hand.js
index 51133350..7e164c09 100644
--- a/client-data/tools/hand/hand.js
+++ b/client-data/tools/hand/hand.js
@@ -87,7 +87,7 @@
     ),
   ];
 
-  for (i in blockedSelectionButtons) {
+  for (var i in blockedSelectionButtons) {
     delete selectionButtons[blockedSelectionButtons[i]];
   }
 
@@ -273,7 +273,7 @@
     selectionRect.width.baseVal.value = 0;
     selectionRect.height.baseVal.value = 0;
     selectionRect.style.display = "";
-    tmatrix = get_transform_matrix(selectionRect);
+    var tmatrix = get_transform_matrix(selectionRect);
     tmatrix.e = 0;
     tmatrix.f = 0;
   }
@@ -284,6 +284,7 @@
     var selected = [];
     for (var i = 0; i < elements.length; i++) {
       if (
+        // eslint-disable-next-line no-undef
         transformedBBoxIntersects(selectionTBBox, elements[i].transformedBBox())
       )
         selected.push(Tools.drawingArea.children[i]);
@@ -421,6 +422,7 @@
 
   function draw(data) {
     if (data._children) {
+      // eslint-disable-next-line no-undef
       batchCall(draw, data._children);
     } else {
       switch (data.type) {
@@ -442,6 +444,7 @@
           break;
         case "delete":
           data.tool = "Eraser";
+          // eslint-disable-next-line no-undef
           messageForTool(data);
           break;
         default:
@@ -463,6 +466,7 @@
     if (button) {
       button.clickCallback(x, y, evt);
     } else if (
+      // eslint-disable-next-line no-undef
       pointInTransformedBBox([x, y], selectionRect.transformedBBox())
     ) {
       hideSelectionButtons();
@@ -477,6 +481,7 @@
     }
   }
 
+  // eslint-disable-next-line no-unused-vars
   function releaseSelector(x, y, evt) {
     if (selectorState == selectorStates.selecting) {
       selected_els = calculateSelection();
@@ -489,6 +494,7 @@
     selectorState = selectorStates.pointing;
   }
 
+  // eslint-disable-next-line no-unused-vars
   function moveSelector(x, y, evt) {
     if (selectorState == selectorStates.selecting) {
       updateRect(x, y, selectionRect);
diff --git a/client-data/tools/pencil/pencil.js b/client-data/tools/pencil/pencil.js
index 36b37d34..9cacfae2 100644
--- a/client-data/tools/pencil/pencil.js
+++ b/client-data/tools/pencil/pencil.js
@@ -156,6 +156,7 @@
 
   function addPoint(line, x, y) {
     var pts = getPathData(line);
+    // eslint-disable-next-line no-undef
     pts = wboPencilPoint(pts, x, y);
     line.setPathData(pts);
   }
@@ -212,6 +213,7 @@
       release: stopLineAt,
     },
     draw: draw,
+    // eslint-disable-next-line no-unused-vars
     onstart: function (oldTool) {
       //Reset stylus
       hasUsedStylus = false;
@@ -225,6 +227,7 @@
         toggleSize();
       },
     },
+    // eslint-disable-next-line no-dupe-keys
     onstart: function () {
       //When switching from another tool to white-out, restore white-out size
       if (pencilTool.secondary.active) {
diff --git a/client-data/tools/text/text.js b/client-data/tools/text/text.js
index 27689740..f1b2b549 100644
--- a/client-data/tools/text/text.js
+++ b/client-data/tools/text/text.js
@@ -58,6 +58,7 @@
     Tools.setSize(curText.oldSize);
   }
 
+  // eslint-disable-next-line no-unused-vars
   function clickHandler(x, y, evt, isTouchEvent) {
     //if(document.querySelector("#menu").offsetWidth>Tools.menu_width+3) return;
     if (evt.target === input) return;
@@ -99,6 +100,7 @@
     active = true;
     if (!input.parentNode) board.appendChild(input);
     input.value = "";
+    // eslint-disable-next-line no-unused-vars
     var left = curText.x - document.documentElement.scrollLeft + "px";
     var clientW = Math.max(
       document.documentElement.clientWidth,
@@ -176,6 +178,7 @@
     }
   }
 
+  // eslint-disable-next-line no-unused-vars
   function draw(data, isLocal) {
     Tools.drawingEvent = true;
     switch (data.type) {
diff --git a/client-data/tools/zoom/zoom.js b/client-data/tools/zoom/zoom.js
index 85c79b63..9a2dd89d 100644
--- a/client-data/tools/zoom/zoom.js
+++ b/client-data/tools/zoom/zoom.js
@@ -153,6 +153,7 @@
   Tools.board.addEventListener("touchend", touchend);
   Tools.board.addEventListener("touchcancel", touchend);
 
+  // eslint-disable-next-line no-unused-vars
   function release(x, y, evt, isTouchEvent) {
     if (pressed && !moved) {
       var delta = evt.shiftKey === true ? -1 : 1;
diff --git a/package.json b/package.json
index 319af6e8..6832a8bc 100644
--- a/package.json
+++ b/package.json
@@ -21,7 +21,8 @@
     "start": "node ./server/server.js",
     "test": "nightwatch tests && nightwatch tests --env jwt",
     "prettier": "prettier . --write",
-    "prettier-check": "prettier . --check"
+    "prettier-check": "prettier . --check",
+    "lint": "eslint ."
   },
   "main": "./server/server.js",
   "repository": {