diff --git a/.DS_Store b/.DS_Store
deleted file mode 100644
index 30bfe61..0000000
Binary files a/.DS_Store and /dev/null differ
diff --git a/.gitignore b/.gitignore
index 074ab52..baadd77 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
+.DS_Store
 package-lock.json
 node_modules
\ No newline at end of file
diff --git a/Gruntfile.js b/Gruntfile.js
index 07320b5..df66994 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -8,7 +8,10 @@ module.exports = function (grunt) {
             'https://github.com/denissdubinin/Javascript-Sudoku - Licensed MIT */\n',
         uglify: {
             options: {
-                banner: '<%= banner %>'
+                banner: '<%= banner %>',
+                output: {
+                    beautify: false
+                }
             },
             dist: {
                 files: {
diff --git a/dist/sudoku.min.css b/dist/sudoku.min.css
index 19b0ed0..0369321 100644
--- a/dist/sudoku.min.css
+++ b/dist/sudoku.min.css
@@ -1,4 +1,4 @@
 /*! Javascript Sudoku v1.0.0 by Deniss Dubinin - https://github.com/denissdubinin/Javascript-Sudoku - Licensed MIT */
 
-.sudoku{margin:0 auto;position:relative;width:370px}.sudoku.loading::after{background:#fff;content:'';cursor:not-allowed;display:block;height:100%;left:0;opacity:.5;position:absolute;top:0;width:100%}.sudoku table{width:370px;height:370px}.sudoku .sudoku-cell{padding:0}.sudoku .sudoku-cell.invalid-cell input{background:#f9d4d4}.sudoku tr:nth-of-type(3n){border-bottom:2px solid #c5c5c5}.sudoku tr:last-of-type{border-bottom:none}.sudoku td:nth-of-type(3n){border-right:2px solid #c5c5c5}.sudoku td:last-of-type{border-right:none}.sudoku input{border:0;height:100%;text-align:center;width:100%}.sudoku input:disabled{background:#f5f5f5;cursor:not-allowed}
+/*! Javascript Sudoku v1.0.0 by Deniss Dubinin - https://github.com/denissdubinin/Javascript-Sudoku - Licensed MIT */.sudoku{margin:0 auto;position:relative;width:370px}.sudoku.loading::after{background:#fff;content:'';cursor:not-allowed;display:block;height:100%;left:0;opacity:.5;position:absolute;top:0;width:100%}.sudoku table{width:370px;height:370px}.sudoku .sudoku-cell{padding:0}.sudoku .sudoku-cell.invalid-cell input{background:#f9d4d4}.sudoku tr:nth-of-type(3n){border-bottom:2px solid #c5c5c5}.sudoku tr:last-of-type{border-bottom:none}.sudoku td:nth-of-type(3n){border-right:2px solid #c5c5c5}.sudoku td:last-of-type{border-right:none}.sudoku input{border:0;height:100%;text-align:center;width:100%}.sudoku input:disabled{background:#f5f5f5;cursor:not-allowed}.sudoku input.timer-disabled{cursor:not-allowed}
 /*# sourceMappingURL=sudoku.min.css.map */
diff --git a/dist/sudoku.min.css.map b/dist/sudoku.min.css.map
index e130807..1cb493e 100644
--- a/dist/sudoku.min.css.map
+++ b/dist/sudoku.min.css.map
@@ -1,6 +1,6 @@
 {
 "version": 3,
-"mappings": "AAMA,OAAQ,CACJ,MAAM,CAAE,MAAM,CACd,QAAQ,CAAE,QAAQ,CAClB,KAAK,CAAE,KAAK,CAEZ,sBAAiB,CACb,UAAU,CAAE,IAAI,CAChB,OAAO,CAAE,EAAE,CACX,MAAM,CAAE,WAAW,CACnB,OAAO,CAAE,KAAK,CACd,MAAM,CAAE,IAAI,CACZ,IAAI,CAAE,CAAC,CACP,OAAO,CAAE,EAAE,CACX,QAAQ,CAAE,QAAQ,CAClB,GAAG,CAAE,CAAC,CACN,KAAK,CAAE,IAAI,CAGf,aAAM,CACF,KAAK,CAAE,KAAK,CACZ,MAAM,CAAE,KAAK,CAGjB,oBAAa,CACT,OAAO,CAAE,CAAC,CAEV,uCAAqB,CACjB,UAAU,CAAE,OAAO,CAKvB,0BAAkB,CACd,aAAa,CAAE,iBAAiB,CAGpC,uBAAe,CACX,aAAa,CAAE,IAAI,CAKvB,0BAAkB,CACd,YAAY,CAAE,iBAAiB,CAGnC,uBAAe,CACX,YAAY,CAAE,IAAI,CAI1B,aAAM,CACF,MAAM,CAAE,CAAC,CACT,MAAM,CAAE,IAAI,CACZ,UAAU,CAAE,MAAM,CAClB,KAAK,CAAE,IAAI,CAEX,sBAAW,CACP,UAAU,CAAE,OAAO,CACnB,MAAM,CAAE,WAAW",
+"mappings": "AAAA,qHAAqH,AAErH,OAAQ,CACJ,MAAM,CAAE,MAAM,CACd,QAAQ,CAAE,QAAQ,CAClB,KAAK,CAAE,KAAK,CAEZ,sBAAiB,CACb,UAAU,CAAE,IAAI,CAChB,OAAO,CAAE,EAAE,CACX,MAAM,CAAE,WAAW,CACnB,OAAO,CAAE,KAAK,CACd,MAAM,CAAE,IAAI,CACZ,IAAI,CAAE,CAAC,CACP,OAAO,CAAE,EAAE,CACX,QAAQ,CAAE,QAAQ,CAClB,GAAG,CAAE,CAAC,CACN,KAAK,CAAE,IAAI,CAGf,aAAM,CACF,KAAK,CAAE,KAAK,CACZ,MAAM,CAAE,KAAK,CAGjB,oBAAa,CACT,OAAO,CAAE,CAAC,CAEV,uCAAqB,CACjB,UAAU,CAAE,OAAO,CAKvB,0BAAkB,CACd,aAAa,CAAE,iBAAiB,CAGpC,uBAAe,CACX,aAAa,CAAE,IAAI,CAKvB,0BAAkB,CACd,YAAY,CAAE,iBAAiB,CAGnC,uBAAe,CACX,YAAY,CAAE,IAAI,CAI1B,aAAM,CACF,MAAM,CAAE,CAAC,CACT,MAAM,CAAE,IAAI,CACZ,UAAU,CAAE,MAAM,CAClB,KAAK,CAAE,IAAI,CAEX,sBAAW,CACP,UAAU,CAAE,OAAO,CACnB,MAAM,CAAE,WAAW,CAGvB,4BAAiB,CACb,MAAM,CAAE,WAAW",
 "sources": ["../src/sudoku.scss"],
 "names": [],
 "file": "sudoku.min.css"
diff --git a/dist/sudoku.min.js b/dist/sudoku.min.js
index 4c43beb..50e336a 100644
--- a/dist/sudoku.min.js
+++ b/dist/sudoku.min.js
@@ -1,3 +1,3 @@
 /*! Javascript Sudoku v1.0.0 by Deniss Dubinin - https://github.com/denissdubinin/Javascript-Sudoku - Licensed MIT */
 
-"use strict";window.sudoku={Valve:"Trilogy"},function(window,$){$.fn.Sudoku=function(options){var defaults={defaultSquare:3,dropTimerOnReset:!0,markWrongCellsOnFly:!1,markWrongCellsOnFinish:!0,useTimer:!0,timerOnly:!0,sudokuMixIterations:500},options=$.extend({},defaults,options),sudokuTimer;function create(o){generateGui(o),init()}function init(){toggleLoadingOverlay(!0),generateMatrix(),mixMatrix(),prepareEmptyMatrix(),fillGrid()}function generateGui(o){o.prepend('<label id="sudoku-minutes">00</label>:<label id="sudoku-seconds">00</label>'),$('<table class="table table-bordered"></table>').appendTo(o);for(var t=0,u=0;t<9;){for(var n=$('<tr class="sudoku-row"></tr>').appendTo(o.find("table"));u<9;)$('<td class="sudoku-cell"><input size="1" maxlength="1" onkeypress="return window.sudoku.listenKeyPress(event);"></td>').appendTo(n),u++;u=0,t++}initGridButtons(o)}function checkSudokuSuccess(){if(!$(".sudoku-cell").find("input").filter(function(){return""===this.value}).length){var o=[];$(".sudoku .sudoku-row").each(function(t){o.push([]),$(this).find("input").each(function(){o[t].push(parseInt($(this).val()))})}),checkResults(o,window.sudoku.fullMatrix)&&$(document).trigger("startConfetti")}}function toggleLoadingOverlay(o){o?$(".sudoku").addClass("loading"):$(".sudoku").removeClass("loading")}function initGridButtons(o){var t=$("<div>").addClass("btn-group"),u=$("<button>").addClass("btn btn-success btn-sm").attr("id","start-sudoku").text("Start"),n=$("<button>").addClass("btn btn-danger btn-sm").attr("id","r-sudoku").text("Reset sudoku"),e=$("<button>").addClass("btn btn-primary btn-sm").attr("id","gn-sudoku").text("Generate new sudoku");t.append(u).append(n).append(e),o.append(t),$("#start-sudoku").on("click",function(){initTimer(),$("#start-sudoku").prop("disabled",!0)}),$("#r-sudoku").on("click",function(){1==confirm("Are you sure?")&&(fillGrid(),$(".sudoku-cell").removeClass("invalid-cell"),options.dropTimerOnReset&&resetTimer(!1))}),$("#gn-sudoku").on("click",function(){1==confirm("Are you sure?")&&($(document).trigger("stopConfetti"),$(".sudoku-cell input:disabled").prop("disabled",!1),$("#start-sudoku").prop("disabled",!1),$(".sudoku-cell").removeClass("invalid-cell"),resetTimer(!0),init())})}function initTimer(){var o=$("#sudoku-minutes"),t=$("#sudoku-seconds"),u=0;function n(o){var t=o+"";return t.length<2?"0"+t:t}sudokuTimer=setInterval(function(){++u,t.text(n(u%60)),o.text(n(parseInt(u/60)))},1e3)}function resetTimer(o){$("#sudoku-minutes, #sudoku-seconds").text("00"),clearInterval(sudokuTimer),o?$("#start-sudoku").prop("disabled",!1):initTimer()}function stopTimer(){clearInterval(sudokuTimer)}function generateMatrix(){var o=options.defaultSquare,t=[];for(let e=0;e<9;e++){var u=[];for(let t=0;t<9;t++){var n=(e*o+e/o+t)%(o*o)+1;u.push(parseInt(n))}t.push(u)}window.sudoku.fullMatrix=t}function fillGrid(){$(".sudoku-row").each(function(o){$(this).find("td").each(function(t){var u=window.sudoku.emptyMatrix[o][t],n=$(this).find("input");n.val(u),""!==u&&n.prop("disabled",!0)})}),toggleLoadingOverlay(!1),$(".sudoku-cell input").off("input"),$(".sudoku-cell input").on("input",function(){checkSudokuSuccess()})}function transposeMatrix(){return window.sudoku.fullMatrix=window.sudoku.fullMatrix[0].map(function(o,t){return window.sudoku.fullMatrix.map(function(o){return o[t]})}),window.sudoku.fullMatrix}function swapTwoRows(){for(var o=Math.floor(Math.random()*options.defaultSquare),t=Math.floor(Math.random()*options.defaultSquare),u=Math.floor(Math.random()*options.defaultSquare),n=o*options.defaultSquare+t;t==u;)u=Math.floor(Math.random()*options.defaultSquare);var e=o*options.defaultSquare+u,a=window.sudoku.fullMatrix[n],i=window.sudoku.fullMatrix[e];return window.sudoku.fullMatrix[n]=i,window.sudoku.fullMatrix[e]=a,window.sudoku.fullMatrix}function swapTwoColumns(){transposeMatrix(),swapTwoRows(),transposeMatrix()}function swapTwoLargeRows(){for(var o=Math.floor(Math.random()*options.defaultSquare),t=Math.floor(Math.random()*options.defaultSquare);o==t;)t=Math.floor(Math.random()*options.defaultSquare);for(let i=0;i<options.defaultSquare;i++){var u=o*options.defaultSquare+i,n=t*options.defaultSquare+i,e=window.sudoku.fullMatrix[u],a=window.sudoku.fullMatrix[n];window.sudoku.fullMatrix[u]=a,window.sudoku.fullMatrix[n]=e}return window.sudoku.fullMatrix}function swapTwoLargeColumns(){transposeMatrix(),swapTwoLargeRows(),transposeMatrix()}function mixMatrix(){var t0=performance.now(),logicFunctions=["transposeMatrix()","swapTwoRows()","swapTwoRows()","swapTwoColumns()","swapTwoColumns()","swapTwoLargeRows()","swapTwoLargeColumns()"];let i=0;for(;i<options.sudokuMixIterations;){var randomFunction=Math.floor(Math.random()*logicFunctions.length);eval(logicFunctions[randomFunction]),i++}var t1=performance.now();window.sudoku.generationTime=(.001*(t1-t0)).toFixed(5)+" seconds."}function prepareEmptyMatrix(){window.sudoku.emptyMatrix=[];for(let o=0;o<options.defaultSquare*options.defaultSquare;o++){window.sudoku.emptyMatrix.push([]);for(let t=0;t<options.defaultSquare*options.defaultSquare;t++)window.sudoku.emptyMatrix[o].push("")}let o=0;for(;o<options.defaultSquare**4;){let t=Math.floor(Math.random()*options.defaultSquare**2),u=Math.floor(Math.random()*options.defaultSquare**2);""===window.sudoku.emptyMatrix[t][u]&&(o++,10*Math.random()>6&&(window.sudoku.emptyMatrix[t][u]=window.sudoku.fullMatrix[t][u]))}}function checkResults(o,t){let u=!1;for(let e=0;e<o.length;e++)for(let a=0;a<o.length;a++){var n=$(`.sudoku-row:eq(${e}) .sudoku-cell:eq(${a})`);o[e][a]!==t[e][a]?(u=!0,options.markWrongCellsOnFinish&&n.addClass("invalid-cell")):n.removeClass("invalid-cell")}return!u}create($(this)),window.sudoku.listenKeyPress=function(o){var t=window.event?o.keyCode:o.which;return 8==o.keyCode||46==o.keyCode||t>47&&t<58}}}(window,jQuery);
\ No newline at end of file
+"use strict";window.sudoku={Valve:"Trilogy"},function(window,$){$.fn.Sudoku=function(options){var defaults={squareSize:3,dropTimerOnReset:!0,markWrongCellsOnFly:!1,markWrongCellsOnFinish:!0,useTimer:!0,timerOnly:!0,useCustomButtons:!1,sudokuMixIterations:500},options=$.extend({},defaults,options),sudokuTimer;function create(o){o.addClass("sudoku"),generateGui(o),init()}function init(){toggleLoadingOverlay(!0),generateMatrix(),mixMatrix(),prepareEmptyMatrix(),fillGrid(),enableFields(!1)}function generateGui(o){options.useTimer&&o.prepend('<label id="sudoku-minutes">00</label>:<label id="sudoku-seconds">00</label>'),$('<table class="table table-bordered"></table>').appendTo(o);for(var e=0,t=0;e<options.squareSize**2;){for(var n=$('<tr class="sudoku-row"></tr>').appendTo(o.find("table"));t<options.squareSize**2;)$('<td class="sudoku-cell"><input size="1" maxlength="1" onkeypress="return window.sudoku.listenKeyPress(event);"></td>').appendTo(n),t++;t=0,e++}enableFields(!1),initGridButtons(o)}function validateSudoku(o){var e=$(".sudoku-cell").find("input").filter(function(){return""===this.value});if(options.markWrongCellsOnFly){var t=$(o).parent(),n=t.parent().index(),i=t.index();parseInt($(o).val())===window.sudoku.fullMatrix[n][i]||""===$(o).val()?t.removeClass("invalid-cell"):t.addClass("invalid-cell")}if(options.markWrongCellsOnFinish&&!e.length){var s=[];$(".sudoku .sudoku-row").each(function(o){s.push([]),$(this).find("input").each(function(){s[o].push(parseInt($(this).val()))})}),checkResults(s,window.sudoku.fullMatrix)&&$(document).trigger("startConfetti")}}function toggleLoadingOverlay(o){o?$(".sudoku").addClass("loading"):$(".sudoku").removeClass("loading")}function initGridButtons(o){var e=$("<div>").addClass("btn-group"),t=$("<button>").addClass("btn btn-danger btn-sm").attr("id","r-sudoku").text("Reset sudoku"),n=$("<button>").addClass("btn btn-primary btn-sm").attr("id","gn-sudoku").text("Generate new sudoku");if(options.useTimer){var i=$("<button>").addClass("btn btn-success btn-sm").attr("id","start-sudoku").text("Start");e.append(i),i.on("click",function(){initTimer(),enableFields(!0),i.prop("disabled",!0)})}e.append(t).append(n),o.append(e),$("#r-sudoku").on("click",function(){1==confirm("Are you sure?")&&(fillGrid(),$(".sudoku-cell").removeClass("invalid-cell"),options.useTimer&&options.dropTimerOnReset&&resetTimer(!1))}),$("#gn-sudoku").on("click",function(){1==confirm("Are you sure?")&&($(document).trigger("stopConfetti"),$(".sudoku-cell input:disabled:not(.default-cell)").prop("disabled",!1),$(".sudoku-cell").removeClass("invalid-cell"),$(".sudoku-cell input.default-cell").removeClass("default-cell"),options.useTimer&&($("#start-sudoku:not(.default-cell)").prop("disabled",!1),resetTimer(!0)),init())})}function enableFields(o){options.timerOnly&&options.useTimer&&(o?$(".sudoku-cell input:not(.default-cell)").prop("disabled",!1):$(".sudoku-cell input:not(.default-cell)").prop("disabled",!0))}function initTimer(){var o=$("#sudoku-minutes"),e=$("#sudoku-seconds"),t=0;function n(o){var e=o+"";return e.length<2?"0"+e:e}sudokuTimer=setInterval(function(){++t,e.text(n(t%60)),o.text(n(parseInt(t/60)))},1e3)}function resetTimer(o){$("#sudoku-minutes, #sudoku-seconds").text("00"),clearInterval(sudokuTimer),o?$("#start-sudoku").prop("disabled",!1):initTimer()}function stopTimer(){clearInterval(sudokuTimer)}function generateMatrix(){var o=options.squareSize,e=[];for(let i=0;i<options.squareSize**2;i++){var t=[];for(let e=0;e<options.squareSize**2;e++){var n=(i*o+i/o+e)%(o*o)+1;t.push(parseInt(n))}e.push(t)}window.sudoku.fullMatrix=e}function fillGrid(){$(".sudoku-row").each(function(o){$(this).find("td").each(function(e){var t=window.sudoku.emptyMatrix[o][e],n=$(this).find("input");n.val(t),""!==t&&n.prop("disabled",!0).addClass("default-cell")})}),toggleLoadingOverlay(!1),$(".sudoku-cell input").off("input").on("input",function(o){validateSudoku(o.target)})}function transposeMatrix(){return window.sudoku.fullMatrix=window.sudoku.fullMatrix[0].map(function(o,e){return window.sudoku.fullMatrix.map(function(o){return o[e]})}),window.sudoku.fullMatrix}function swapTwoRows(){for(var o=Math.floor(Math.random()*options.squareSize),e=Math.floor(Math.random()*options.squareSize),t=Math.floor(Math.random()*options.squareSize),n=o*options.squareSize+e;e==t;)t=Math.floor(Math.random()*options.squareSize);var i=o*options.squareSize+t,s=window.sudoku.fullMatrix[n],u=window.sudoku.fullMatrix[i];return window.sudoku.fullMatrix[n]=u,window.sudoku.fullMatrix[i]=s,window.sudoku.fullMatrix}function swapTwoColumns(){transposeMatrix(),swapTwoRows(),transposeMatrix()}function swapTwoLargeRows(){for(var o=Math.floor(Math.random()*options.squareSize),e=Math.floor(Math.random()*options.squareSize);o==e;)e=Math.floor(Math.random()*options.squareSize);for(let u=0;u<options.squareSize;u++){var t=o*options.squareSize+u,n=e*options.squareSize+u,i=window.sudoku.fullMatrix[t],s=window.sudoku.fullMatrix[n];window.sudoku.fullMatrix[t]=s,window.sudoku.fullMatrix[n]=i}return window.sudoku.fullMatrix}function swapTwoLargeColumns(){transposeMatrix(),swapTwoLargeRows(),transposeMatrix()}function mixMatrix(){var t0=performance.now(),logicFunctions=["transposeMatrix()","swapTwoRows()","swapTwoRows()","swapTwoColumns()","swapTwoColumns()","swapTwoLargeRows()","swapTwoLargeColumns()"];let i=0;for(;i<options.sudokuMixIterations;){var randomFunction=Math.floor(Math.random()*logicFunctions.length);eval(logicFunctions[randomFunction]),i++}var t1=performance.now();window.sudoku.generationTime=(.001*(t1-t0)).toFixed(5)+" seconds."}function prepareEmptyMatrix(){window.sudoku.emptyMatrix=[];for(let o=0;o<options.squareSize*options.squareSize;o++){window.sudoku.emptyMatrix.push([]);for(let e=0;e<options.squareSize*options.squareSize;e++)window.sudoku.emptyMatrix[o].push("")}let o=0;for(;o<options.squareSize**4;){let e=Math.floor(Math.random()*options.squareSize**2),t=Math.floor(Math.random()*options.squareSize**2);""===window.sudoku.emptyMatrix[e][t]&&(o++,10*Math.random()>6&&(window.sudoku.emptyMatrix[e][t]=window.sudoku.fullMatrix[e][t]))}}function checkResults(o,e){let t=!1;for(let i=0;i<o.length;i++)for(let s=0;s<o.length;s++){var n=$(`.sudoku-row:eq(${i}) .sudoku-cell:eq(${s})`);o[i][s]!==e[i][s]?(t=!0,options.markWrongCellsOnFinish&&n.addClass("invalid-cell")):n.removeClass("invalid-cell")}return!t}create($(this)),window.sudoku.listenKeyPress=function(o){var e=window.event?o.keyCode:o.which;return 8==o.keyCode||46==o.keyCode||e>47&&e<58}}}(window,jQuery);
\ No newline at end of file
diff --git a/src/sudoku.js b/src/sudoku.js
index cb63dce..71c658a 100644
--- a/src/sudoku.js
+++ b/src/sudoku.js
@@ -5,16 +5,17 @@ window.sudoku = {
     'Valve': 'Trilogy'
 };
 
-(function(window, $) {
-    $.fn.Sudoku = function(options) {
+(function (window, $) {
+    $.fn.Sudoku = function (options) {
         var defaults = {
                 // TODO: ADD POSSIBILITY TO HAVE 2 SUDOKU ON 1 PAGE
-                defaultSquare: 3, // TODO: GRID GENERATION
+                squareSize: 3, // TODO: GRID GENERATION
                 dropTimerOnReset: true,
-                markWrongCellsOnFly: false, // TODO: NOT IMPLEMENTED AT ALL
+                markWrongCellsOnFly: false,
                 markWrongCellsOnFinish: true,
-                useTimer: true, // TODO: NOT IMPLEMENT AT ALL
-                timerOnly: true, // TODO: WTF IS THIS? START ONLY WITH TIMER ENABLED?!?!?!
+                useTimer: true,
+                timerOnly: true,
+                useCustomButtons: false, // TODO: NOT IMPLEMENT AT ALL
                 sudokuMixIterations: 500
             },
             options = $.extend({}, defaults, options),
@@ -24,9 +25,10 @@ window.sudoku = {
 
         /**
          * Initialise script
-         * @param {element} element 
+         * @param {object} element 
          */
         function create(element) {
+            element.addClass('sudoku');
             generateGui(element);
             init();
         }
@@ -40,6 +42,7 @@ window.sudoku = {
             mixMatrix();
             prepareEmptyMatrix();
             fillGrid();
+            enableFields(false);
         }
 
         /**
@@ -47,14 +50,17 @@ window.sudoku = {
          * @param {object} element 
          */
         function generateGui(element) {
-            element.prepend('<label id="sudoku-minutes">00</label>:<label id="sudoku-seconds">00</label>');
+            if (options.useTimer) {
+                element.prepend('<label id="sudoku-minutes">00</label>:<label id="sudoku-seconds">00</label>');
+            }
+
             $('<table class="table table-bordered"></table>').appendTo(element);
             var i = 0,
                 k = 0;
 
-            while (i < 9) {
+            while (i < options.squareSize ** 2) {
                 var row = $('<tr class="sudoku-row"></tr>').appendTo(element.find('table'));
-                while (k < 9) {
+                while (k < options.squareSize ** 2) {
                     $('<td class="sudoku-cell"><input size="1" maxlength="1" onkeypress="return window.sudoku.listenKeyPress(event);"></td>').appendTo(row);
                     k++;
                 }
@@ -62,6 +68,7 @@ window.sudoku = {
                 i++;
             }
 
+            enableFields(false);
             initGridButtons(element);
         }
 
@@ -75,19 +82,37 @@ window.sudoku = {
             if ((event.keyCode == 8 || event.keyCode == 46) || (key > 47 && key < 58)) {
                 return true;
             }
-            
+
             return false;
         }
 
-        function checkSudokuSuccess() {
-            var emptyCells = $('.sudoku-cell').find('input').filter(function() {
+        /**
+         * Validate sudoku and mark invalid cells
+         * @param {object} element
+         */
+        function validateSudoku(element) {
+            var emptyCells = $('.sudoku-cell').find('input').filter(function () {
                 return this.value === '';
             });
 
-            if (!emptyCells.length) {
+            if (options.markWrongCellsOnFly) {
+                var cell = $(element).parent(),
+                    rowPos = cell.parent().index(),
+                    colPos = cell.index();
+
+                if (parseInt($(element).val()) === window.sudoku.fullMatrix[rowPos][colPos] ||
+                    $(element).val() === ''
+                ) {
+                    cell.removeClass('invalid-cell');
+                } else {
+                    cell.addClass('invalid-cell');
+                }
+            }
+
+            if (options.markWrongCellsOnFinish && !emptyCells.length) {
                 var filledMatrix = [];
 
-                $('.sudoku .sudoku-row').each(function(index) {
+                $('.sudoku .sudoku-row').each(function (index) {
                     filledMatrix.push([]);
                     $(this).find('input').each(function () {
                         filledMatrix[index].push(parseInt($(this).val()));
@@ -96,13 +121,12 @@ window.sudoku = {
 
                 if (checkResults(filledMatrix, window.sudoku.fullMatrix)) {
                     $(document).trigger('startConfetti');
-                } else {
                 }
             }
         }
 
         /**
-         * Toggle sudoku loading overlay
+         * Toggle sudoku loading overlay | TODO
          * @param {bool} enable 
          */
         function toggleLoadingOverlay(enable) {
@@ -119,50 +143,77 @@ window.sudoku = {
          */
         function initGridButtons(element) {
             var buttonGroup = $('<div>').addClass('btn-group'),
-                startButton = $('<button>').addClass('btn btn-success btn-sm')
-                    .attr('id', 'start-sudoku')
-                    .text('Start'),
                 resetButton = $('<button>').addClass('btn btn-danger btn-sm')
-                    .attr('id', 'r-sudoku')
-                    .text('Reset sudoku'),
+                .attr('id', 'r-sudoku').text('Reset sudoku'),
                 generateButton = $('<button>').addClass('btn btn-primary btn-sm')
-                    .attr('id', 'gn-sudoku')
-                    .text('Generate new sudoku');
+                .attr('id', 'gn-sudoku').text('Generate new sudoku');
+
+            if (options.useTimer) {
+                var startButton = $('<button>').addClass('btn btn-success btn-sm')
+                    .attr('id', 'start-sudoku').text('Start');
+
+                buttonGroup.append(startButton);
+
+                startButton.on('click', function () {
+                    initTimer(); // DOENST WORK, NOT INITIALISED YET
+                    enableFields(true);
+                    startButton.prop('disabled', true);
+                });
+            }
 
-            buttonGroup.append(startButton).append(resetButton)
-                .append(generateButton);
+            buttonGroup.append(resetButton).append(generateButton);
             element.append(buttonGroup);
 
-            $('#start-sudoku').on('click', function() {
-                initTimer();
-                $('#start-sudoku').prop('disabled', true);
-            });
-            $('#r-sudoku').on('click', function() {
+            $('#r-sudoku').on('click', function () {
                 var popup = confirm('Are you sure?');
                 if (popup == true) {
                     fillGrid();
                     $('.sudoku-cell').removeClass('invalid-cell');
 
-                    if (options.dropTimerOnReset) {
+                    if (options.useTimer && options.dropTimerOnReset) {
                         resetTimer(false);
                     }
                 }
             });
-            $('#gn-sudoku').on('click', function() {
+
+            $('#gn-sudoku').on('click', function () {
                 var popup = confirm('Are you sure?');
                 if (popup == true) {
                     $(document).trigger('stopConfetti');
-                    $('.sudoku-cell input:disabled').prop('disabled', false);
-                    $('#start-sudoku').prop('disabled', false);
+                    $('.sudoku-cell input:disabled:not(.default-cell)').prop('disabled', false);
                     $('.sudoku-cell').removeClass('invalid-cell');
-                    resetTimer(true);
+                    $('.sudoku-cell input.default-cell').removeClass('default-cell');
+
+                    if (options.useTimer) {
+                        $('#start-sudoku:not(.default-cell)').prop('disabled', false);
+                        resetTimer(true);
+                    }
+
                     init();
                 }
             });
         }
 
+        /**
+         * Toggle input fields
+         * Triggered only if options.timerOnly === true and options.useTimer === true
+         * @param {bool} enable 
+         */
+        function enableFields(enable) {
+            if (!options.timerOnly || !options.useTimer) {
+                return;
+            }
+
+            if (enable) {
+                $('.sudoku-cell input:not(.default-cell)').prop('disabled', false);
+            } else {
+                $('.sudoku-cell input:not(.default-cell)').prop('disabled', true);
+            }
+        }
+
         /**
          * Initialise playing timer
+         * Triggered only if options.useTimer === true
          */
         function initTimer() {
             var minutesLabel = $('#sudoku-minutes'),
@@ -189,6 +240,7 @@ window.sudoku = {
 
         /**
          * Reset timer on new sudoku start on reset
+         * Triggered only if options.useTimer === true
          * @param {bool} stopTimer
          */
         function resetTimer(stopTimer) {
@@ -214,11 +266,11 @@ window.sudoku = {
          * Generate sudoku matrix
          */
         function generateMatrix() {
-            var n = options.defaultSquare,
+            var n = options.squareSize,
                 result = [];
-            for (let i = 0; i < 9; i++) {
+            for (let i = 0; i < options.squareSize ** 2; i++) {
                 var row = [];
-                for (let j = 0; j < 9; j++) {
+                for (let j = 0; j < options.squareSize ** 2; j++) {
                     var val = ((i * n + i / n + j) % (n * n) + 1);
                     row.push(parseInt(val));
                 }
@@ -232,24 +284,23 @@ window.sudoku = {
          * Fill sudoku grid with numbers
          */
         function fillGrid() {
-            $('.sudoku-row').each(function(i) {
-                $(this).find('td').each(function(j) {
+            $('.sudoku-row').each(function (i) {
+                $(this).find('td').each(function (j) {
                     var val = window.sudoku.emptyMatrix[i][j],
                         input = $(this).find('input');
 
                     input.val(val);
 
                     if (val !== '') {
-                        input.prop('disabled', true);
+                        input.prop('disabled', true).addClass('default-cell');
                     }
                 });
             });
 
             toggleLoadingOverlay(false);
 
-            $('.sudoku-cell input').off('input');
-            $('.sudoku-cell input').on('input', function () {
-                checkSudokuSuccess();
+            $('.sudoku-cell input').off('input').on('input', function (event) {
+                validateSudoku(event.target);
             });
         }
 
@@ -257,8 +308,8 @@ window.sudoku = {
          * Transpose matrix
          */
         function transposeMatrix() {
-            window.sudoku.fullMatrix = window.sudoku.fullMatrix[0].map(function(i, k) {
-                return window.sudoku.fullMatrix.map(function(array) {
+            window.sudoku.fullMatrix = window.sudoku.fullMatrix[0].map(function (i, k) {
+                return window.sudoku.fullMatrix.map(function (array) {
                     return array[k]
                 });
             });
@@ -270,16 +321,16 @@ window.sudoku = {
          * Swap two random rows in matrix
          */
         function swapTwoRows() {
-            var areaToSwap = Math.floor(Math.random() * options.defaultSquare),
-                line1 = Math.floor(Math.random() * options.defaultSquare),
-                line2 = Math.floor(Math.random() * options.defaultSquare),
-                row1 = areaToSwap * options.defaultSquare + line1;
+            var areaToSwap = Math.floor(Math.random() * options.squareSize),
+                line1 = Math.floor(Math.random() * options.squareSize),
+                line2 = Math.floor(Math.random() * options.squareSize),
+                row1 = areaToSwap * options.squareSize + line1;
 
             while (line1 == line2) {
-                line2 = Math.floor(Math.random() * options.defaultSquare);
+                line2 = Math.floor(Math.random() * options.squareSize);
             }
 
-            var row2 = areaToSwap * options.defaultSquare + line2,
+            var row2 = areaToSwap * options.squareSize + line2,
                 oldRowData1 = window.sudoku.fullMatrix[row1],
                 oldRowData2 = window.sudoku.fullMatrix[row2];
 
@@ -302,16 +353,16 @@ window.sudoku = {
          * Swap two random large rows (x3 rows) in matrix
          */
         function swapTwoLargeRows() {
-            var areaToSwap1 = Math.floor(Math.random() * options.defaultSquare),
-                areaToSwap2 = Math.floor(Math.random() * options.defaultSquare);
+            var areaToSwap1 = Math.floor(Math.random() * options.squareSize),
+                areaToSwap2 = Math.floor(Math.random() * options.squareSize);
 
             while (areaToSwap1 == areaToSwap2) {
-                areaToSwap2 = Math.floor(Math.random() * options.defaultSquare);
+                areaToSwap2 = Math.floor(Math.random() * options.squareSize);
             }
 
-            for (let i = 0; i < options.defaultSquare; i++) {
-                var row1 = areaToSwap1 * options.defaultSquare + i,
-                    row2 = areaToSwap2 * options.defaultSquare + i,
+            for (let i = 0; i < options.squareSize; i++) {
+                var row1 = areaToSwap1 * options.squareSize + i,
+                    row2 = areaToSwap2 * options.squareSize + i,
                     oldLargeRowData1 = window.sudoku.fullMatrix[row1],
                     oldLargeRowData2 = window.sudoku.fullMatrix[row2];
                 window.sudoku.fullMatrix[row1] = oldLargeRowData2;
@@ -362,22 +413,22 @@ window.sudoku = {
         function prepareEmptyMatrix() {
             window.sudoku.emptyMatrix = [];
 
-            for (let i = 0; i < options.defaultSquare * options.defaultSquare; i++) {
+            for (let i = 0; i < options.squareSize * options.squareSize; i++) {
                 window.sudoku.emptyMatrix.push([]);
-                for (let k = 0; k < options.defaultSquare * options.defaultSquare; k++) {
+                for (let k = 0; k < options.squareSize * options.squareSize; k++) {
                     window.sudoku.emptyMatrix[i].push('');
                 }
             }
 
             let iterator = 0;
 
-            while (iterator < options.defaultSquare ** 4) {
-                let i = Math.floor(Math.random() * (options.defaultSquare ** 2)),
-                    j = Math.floor(Math.random() * (options.defaultSquare ** 2));
+            while (iterator < options.squareSize ** 4) {
+                let i = Math.floor(Math.random() * (options.squareSize ** 2)),
+                    j = Math.floor(Math.random() * (options.squareSize ** 2));
                 if (window.sudoku.emptyMatrix[i][j] === '') {
                     iterator++;
 
-                    if (Math.random() * 10 > 6){
+                    if (Math.random() * 10 > 6) {
                         window.sudoku.emptyMatrix[i][j] = window.sudoku.fullMatrix[i][j];
                     }
                 }
diff --git a/src/sudoku.scss b/src/sudoku.scss
index 0c371ef..e400164 100644
--- a/src/sudoku.scss
+++ b/src/sudoku.scss
@@ -24,6 +24,7 @@
     }
 
     .sudoku-cell {
+        text-align: center;
         padding: 0;
 
         &.invalid-cell input {
@@ -61,5 +62,10 @@
             background: #f5f5f5;
             cursor: not-allowed;
         }
+
+        &.timer-disabled {
+            cursor: not-allowed;
+            
+        }
     }
 }