diff --git a/README.md b/README.md
index c0efc5c..6dad6a3 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,11 @@
-# jsplayground
+# JS Playground
+
+This is a small browser-only logic gate simulator. Open `index.html` in a modern
+web browser and drag gates from the sidebar onto the workspace. Connect gate
+pins to create wires, toggle switches by double-clicking them and watch lights
+update live.
+
+Use the **Save** button to download the circuit as a JSON file and **Load** to
+restore a saved design.
+
+Select gates or wires with the mouse and press `Delete` to remove them.
diff --git a/app.js b/app.js
new file mode 100644
index 0000000..8d3705d
--- /dev/null
+++ b/app.js
@@ -0,0 +1,285 @@
+const workspace = document.getElementById('workspace');
+const wiresSvg = document.getElementById('wires');
+const gateOptions = document.querySelectorAll('.gate-option');
+const saveBtn = document.getElementById('save');
+const loadInput = document.getElementById('load');
+const loadBtn = document.getElementById('loadBtn');
+const sidebar = document.getElementById('sidebar');
+
+let gates = [];
+let wires = [];
+let dragData = null;
+let connectData = null;
+let gateId = 0;
+let selectedGate = null;
+let selectedWire = null;
+
+function selectGate(gate) {
+  if (selectedGate && selectedGate.element) {
+    selectedGate.element.classList.remove('selected');
+  }
+  selectedGate = gate;
+  if (gate && gate.element) {
+    gate.element.classList.add('selected');
+  }
+}
+
+function selectWire(wire) {
+  if (selectedWire && selectedWire.el) {
+    selectedWire.el.classList.remove('selected-wire');
+  }
+  selectedWire = wire;
+  if (wire && wire.el) {
+    wire.el.classList.add('selected-wire');
+  }
+}
+
+function createGate(type, x, y) {
+  const gate = {
+    id: gateId++,
+    type,
+    x,
+    y,
+    inputs: [],
+    outputs: [],
+    element: null,
+    state: false,
+  };
+  const el = document.createElement('div');
+  el.classList.add('gate');
+  el.style.left = x + 'px';
+  el.style.top = y + 'px';
+  el.setAttribute('data-id', gate.id);
+  el.innerText = type;
+  if (type === 'SWITCH') el.classList.add('switch');
+  if (type === 'LIGHT') el.classList.add('light');
+  el.addEventListener('mousedown', startDrag);
+  el.addEventListener('click', () => selectGate(gate));
+  workspace.appendChild(el);
+  gate.element = el;
+
+  if (type === 'NOT') {
+    addPin(gate, 'input');
+    addPin(gate, 'output');
+  } else if (type === 'AND' || type === 'OR') {
+    addPin(gate, 'input');
+    addPin(gate, 'input');
+    addPin(gate, 'output');
+  } else if (type === 'SWITCH') {
+    addPin(gate, 'output');
+    el.addEventListener('dblclick', () => {
+      gate.state = !gate.state;
+      el.style.background = gate.state ? '#ff8080' : '#ffe0e0';
+    });
+  } else if (type === 'LIGHT') {
+    addPin(gate, 'input');
+  }
+  gates.push(gate);
+  return gate;
+}
+
+function addPin(gate, kind) {
+  const pin = document.createElement('div');
+  pin.classList.add('pin');
+  pin.classList.add(kind === 'input' ? 'input-pin' : 'output-pin');
+  pin.setAttribute('data-gate', gate.id);
+  pin.setAttribute('data-kind', kind);
+  pin.setAttribute('data-index', kind === 'input' ? gate.inputs.length : gate.outputs.length);
+  pin.addEventListener('mousedown', startConnect);
+  gate.element.appendChild(pin);
+  if (kind === 'input') gate.inputs.push({ state: false, el: pin });
+  else gate.outputs.push({ state: false, el: pin });
+  layoutPins(gate);
+}
+
+function layoutPins(gate) {
+  gate.inputs.forEach((p, i) => { p.el.style.top = (20 * i + 10) + 'px'; });
+  gate.outputs.forEach((p, i) => { p.el.style.top = (20 * i + 10) + 'px'; });
+}
+
+function startDrag(e) {
+  const el = e.currentTarget;
+  dragData = { el, offsetX: e.offsetX, offsetY: e.offsetY };
+  const gid = parseInt(el.getAttribute('data-id'));
+  const gate = gates.find(g => g.id === gid);
+  selectGate(gate);
+  document.addEventListener('mousemove', dragMove);
+  document.addEventListener('mouseup', endDrag);
+}
+
+function dragMove(e) {
+  if (!dragData) return;
+  const x = e.pageX - dragData.offsetX - sidebar.offsetWidth;
+  const y = e.pageY - dragData.offsetY;
+  dragData.el.style.left = x + 'px';
+  dragData.el.style.top = y + 'px';
+  const gate = gates.find(g => g.id == dragData.el.getAttribute('data-id'));
+  gate.x = x;
+  gate.y = y;
+  updateWires();
+}
+
+function endDrag() {
+  dragData = null;
+  document.removeEventListener('mousemove', dragMove);
+  document.removeEventListener('mouseup', endDrag);
+}
+
+function startConnect(e) {
+  e.stopPropagation();
+  const gid = parseInt(e.target.getAttribute('data-gate'));
+  const kind = e.target.getAttribute('data-kind');
+  const idx = parseInt(e.target.getAttribute('data-index'));
+  if (!connectData && kind === 'output') {
+    connectData = { fromGate: gid, fromIndex: idx };
+    selectWire(null);
+  } else if (connectData && kind === 'input') {
+    const wire = { fromGate: connectData.fromGate, fromIndex: connectData.fromIndex, toGate: gid, toIndex: idx, el: null };
+    wires.push(wire);
+    connectData = null;
+    selectWire(wire);
+    updateWires();
+  }
+}
+
+function updateWires() {
+  wiresSvg.innerHTML = '';
+  wires.forEach(w => {
+    const fromGate = gates.find(g => g.id === w.fromGate);
+    const toGate = gates.find(g => g.id === w.toGate);
+    if (!fromGate || !toGate) return;
+    const fromPin = fromGate.outputs[w.fromIndex].el;
+    const toPin = toGate.inputs[w.toIndex].el;
+    const line = document.createElementNS('http://www.w3.org/2000/svg', 'line');
+    const fx = fromGate.x + fromPin.offsetLeft + 5;
+    const fy = fromGate.y + fromPin.offsetTop + 5;
+    const tx = toGate.x + toPin.offsetLeft + 5;
+    const ty = toGate.y + toPin.offsetTop + 5;
+    line.setAttribute('x1', fx);
+    line.setAttribute('y1', fy);
+    line.setAttribute('x2', tx);
+    line.setAttribute('y2', ty);
+    line.setAttribute('stroke', '#000');
+    line.setAttribute('stroke-width', '2');
+    line.style.pointerEvents = 'auto';
+    line.addEventListener('click', (evt) => {
+      evt.stopPropagation();
+      selectWire(w);
+    });
+    wiresSvg.appendChild(line);
+    w.el = line;
+    if (selectedWire === w) {
+      line.classList.add('selected-wire');
+    }
+  });
+}
+
+function evaluate() {
+  gates.forEach(g => g.inputs.forEach(i => i.state = false));
+  wires.forEach(w => {
+    const fromGate = gates.find(g => g.id === w.fromGate);
+    const toGate = gates.find(g => g.id === w.toGate);
+    const value = fromGate.outputs[w.fromIndex].state;
+    toGate.inputs[w.toIndex].state = value;
+  });
+  gates.forEach(g => {
+    if (g.type === 'SWITCH') {
+      g.outputs[0].state = g.state;
+    } else if (g.type === 'AND') {
+      g.outputs[0].state = g.inputs.every(i => i.state);
+    } else if (g.type === 'OR') {
+      g.outputs[0].state = g.inputs.some(i => i.state);
+    } else if (g.type === 'NOT') {
+      g.outputs[0].state = !g.inputs[0].state;
+    } else if (g.type === 'LIGHT') {
+      g.element.style.background = g.inputs[0].state ? '#80ff80' : '#e0ffe0';
+    }
+  });
+}
+
+setInterval(evaluate, 100);
+
+// Drag from sidebar
+gateOptions.forEach(opt => {
+  opt.setAttribute('draggable', 'true');
+  opt.addEventListener('dragstart', e => {
+    e.dataTransfer.setData('text/plain', opt.getAttribute('data-type'));
+  });
+});
+
+workspace.addEventListener('dragover', e => e.preventDefault());
+workspace.addEventListener('drop', e => {
+  const type = e.dataTransfer.getData('text/plain');
+  const x = e.offsetX;
+  const y = e.offsetY;
+  createGate(type, x, y);
+});
+workspace.addEventListener('mousedown', () => {
+  selectGate(null);
+  selectWire(null);
+});
+
+document.addEventListener('keydown', e => {
+  if (e.key === 'Delete') {
+    if (selectedWire) {
+      removeWire(selectedWire);
+    } else if (selectedGate) {
+      removeGate(selectedGate.id);
+    }
+  }
+});
+
+function removeGate(id) {
+  const gate = gates.find(g => g.id === id);
+  if (!gate) return;
+  gate.element.remove();
+  wires = wires.filter(w => w.fromGate !== id && w.toGate !== id);
+  gates = gates.filter(g => g.id !== id);
+  updateWires();
+}
+
+function removeWire(wire) {
+  if (!wire) return;
+  wires = wires.filter(w => w !== wire);
+  if (wire.el) wire.el.remove();
+  selectWire(null);
+  updateWires();
+}
+
+saveBtn.addEventListener('click', () => {
+  const data = {
+    gates: gates.map(g => ({ id: g.id, type: g.type, x: g.x, y: g.y, state: g.state })),
+    wires: wires.map(w => ({ fromGate: w.fromGate, fromIndex: w.fromIndex, toGate: w.toGate, toIndex: w.toIndex }))
+  };
+  const blob = new Blob([JSON.stringify(data)], { type: 'application/json' });
+  const url = URL.createObjectURL(blob);
+  const a = document.createElement('a');
+  a.href = url;
+  a.download = 'circuit.json';
+  a.click();
+  URL.revokeObjectURL(url);
+});
+
+loadBtn.addEventListener('click', () => loadInput.click());
+loadInput.addEventListener('change', e => {
+  const file = e.target.files[0];
+  if (!file) return;
+  const reader = new FileReader();
+  reader.onload = evt => {
+    const data = JSON.parse(evt.target.result);
+    loadCircuit(data);
+  };
+  reader.readAsText(file);
+});
+
+function loadCircuit(data) {
+  gates.forEach(g => g.element.remove());
+  gates = [];
+  wires = [];
+  data.gates.forEach(g => {
+    const gate = createGate(g.type, g.x, g.y);
+    if (g.type === 'SWITCH') gate.state = g.state;
+  });
+  wires = data.wires.map(w => ({ ...w, el: null }));
+  updateWires();
+}
diff --git a/index.html b/index.html
new file mode 100644
index 0000000..8400149
--- /dev/null
+++ b/index.html
@@ -0,0 +1,26 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+<meta charset="UTF-8">
+<title>Logic Gate Simulator</title>
+<link rel="stylesheet" href="style.css">
+</head>
+<body>
+<div id="sidebar">
+  <h3>Gates</h3>
+  <div class="gate-option" data-type="AND">AND</div>
+  <div class="gate-option" data-type="OR">OR</div>
+  <div class="gate-option" data-type="NOT">NOT</div>
+  <div class="gate-option" data-type="SWITCH">Switch</div>
+  <div class="gate-option" data-type="LIGHT">Light</div>
+  <button id="save">Save</button>
+  <input type="file" id="load" style="display:none" />
+  <button id="loadBtn">Load</button>
+</div>
+<div id="workspace-container">
+  <svg id="wires"></svg>
+  <div id="workspace"></div>
+</div>
+<script src="app.js"></script>
+</body>
+</html>
diff --git a/style.css b/style.css
new file mode 100644
index 0000000..be1aae4
--- /dev/null
+++ b/style.css
@@ -0,0 +1,72 @@
+body {
+  margin: 0;
+  font-family: Arial, sans-serif;
+}
+#sidebar {
+  width: 150px;
+  background: #f0f0f0;
+  padding: 10px;
+  box-sizing: border-box;
+  position: fixed;
+  top: 0;
+  bottom: 0;
+  overflow-y: auto;
+}
+#workspace-container {
+  margin-left: 150px;
+  position: relative;
+  height: 100vh;
+}
+#workspace {
+  position: absolute;
+  top: 0;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  background: #fff;
+  overflow: hidden;
+}
+#gates svg {
+  pointer-events: none;
+}
+.gate {
+  position: absolute;
+  border: 1px solid #444;
+  padding: 5px;
+  background: #ddd;
+  cursor: move;
+  user-select: none;
+}
+.gate.selected {
+  border-color: red;
+}
+.pin {
+  width: 10px;
+  height: 10px;
+  background: #666;
+  border-radius: 50%;
+  position: absolute;
+}
+.input-pin {
+  left: -5px;
+}
+.output-pin {
+  right: -5px;
+}
+.switch {
+  background: #ffe0e0;
+}
+.light {
+  background: #e0ffe0;
+}
+svg#wires {
+  position: absolute;
+  top: 0;
+  left: 0;
+  width: 100%;
+  height: 100%;
+  pointer-events: none;
+}
+line.selected-wire {
+  stroke: red;
+}