diff --git a/src/benchmark/benchmark.css b/src/benchmark/benchmark.css
new file mode 100644
index 000000000..e843b5e94
--- /dev/null
+++ b/src/benchmark/benchmark.css
@@ -0,0 +1,7 @@
+@media (min-width: 960px) {
+    .profile-tables {
+        position: absolute;
+        top: 0;
+        left: 520px;
+    }
+}
diff --git a/src/benchmark/benchmark.js b/src/benchmark/benchmark.js
new file mode 100644
index 000000000..d8540404a
--- /dev/null
+++ b/src/benchmark/benchmark.js
@@ -0,0 +1,460 @@
+const Scratch = window.Scratch = window.Scratch || {};
+
+const ASSET_SERVER = 'https://cdn.assets.scratch.mit.edu/';
+const PROJECT_SERVER = 'https://cdn.projects.scratch.mit.edu/';
+
+const SLOW = .1;
+
+const loadProject = function () {
+    let id = location.hash.substring(1);
+    if (id.length < 1 || !isFinite(id)) {
+        id = '119615668';
+    }
+    Scratch.vm.downloadProjectId(id);
+};
+
+/**
+ * @param {Asset} asset - calculate a URL for this asset.
+ * @returns {string} a URL to download a project file.
+ */
+const getProjectUrl = function (asset) {
+    const assetIdParts = asset.assetId.split('.');
+    const assetUrlParts = [PROJECT_SERVER, 'internalapi/project/', assetIdParts[0], '/get/'];
+    if (assetIdParts[1]) {
+        assetUrlParts.push(assetIdParts[1]);
+    }
+    return assetUrlParts.join('');
+};
+
+/**
+ * @param {Asset} asset - calculate a URL for this asset.
+ * @returns {string} a URL to download a project asset (PNG, WAV, etc.)
+ */
+const getAssetUrl = function (asset) {
+    const assetUrlParts = [
+        ASSET_SERVER,
+        'internalapi/asset/',
+        asset.assetId,
+        '.',
+        asset.dataFormat,
+        '/get/'
+    ];
+    return assetUrlParts.join('');
+};
+
+class LoadingProgress {
+    constructor (callback) {
+        this.total = 0;
+        this.complete = 0;
+        this.callback = callback;
+    }
+
+    on (storage) {
+        const _this = this;
+        const _load = storage.webHelper.load;
+        storage.webHelper.load = function (...args) {
+            const result = _load.call(this, ...args);
+            _this.total += 1;
+            _this.callback(_this);
+            result.then(() => {
+                _this.complete += 1;
+                _this.callback(_this);
+            });
+            return result;
+        };
+    }
+}
+
+class StatTable {
+    constructor ({table, keys, viewOf, isSlow}) {
+        this.table = table;
+        if (keys) {
+            this.keys = keys;
+        }
+        if (viewOf) {
+            this.viewOf = viewOf;
+        }
+        if (isSlow) {
+            this.isSlow = isSlow;
+        }
+    }
+
+    render () {
+        const table = this.table;
+        Array.from(table.children)
+            .forEach(node => table.removeChild(node));
+        const keys = this.keys();
+        for (const key of keys) {
+            this.viewOf(key).render({
+                table,
+                isSlow: frame => this.isSlow(key, frame)
+            });
+        }
+    }
+}
+
+class StatView {
+    constructor (name) {
+        this.name = name;
+        this.executions = 0;
+        this.selfTime = 0;
+        this.totalTime = 0;
+    }
+
+    update (selfTime, totalTime) {
+        this.executions++;
+        this.selfTime += selfTime;
+        this.totalTime += totalTime;
+    }
+
+    render ({table, isSlow}) {
+        const row = document.createElement('tr');
+        let cell = document.createElement('td');
+        cell.innerText = this.name;
+        row.appendChild(cell);
+
+        if (isSlow(this)) {
+            row.setAttribute('class', 'slow');
+        }
+
+        cell = document.createElement('td');
+        cell.innerText = (this.selfTime / 1000).toPrecision(3);
+        row.appendChild(cell);
+
+        cell = document.createElement('td');
+        cell.innerText = (this.totalTime / 1000).toPrecision(3);
+        row.appendChild(cell);
+
+        cell = document.createElement('td');
+        cell.innerText = this.executions;
+        row.appendChild(cell);
+
+        table.appendChild(row);
+    }
+}
+
+class RunningStats {
+    constructor (profiler) {
+        this.stepThreadsInnerId = profiler.idByName('Sequencer.stepThreads#inner');
+        this.blockFunctionId = profiler.idByName('blockFunction');
+        this.stpeThreadsId = profiler.idByName('Sequencer.stepThreads');
+
+        this.recordedTime = 0;
+        this.executed = {
+            steps: 0,
+            blocks: 0
+        };
+    }
+
+    update (id, selfTime, totalTime) {
+        if (id === this.stpeThreadsId) {
+            this.recordedTime += totalTime;
+        } else if (id === this.stepThreadsInnerId) {
+            this.executed.steps++;
+        } else if (id === this.blockFunctionId) {
+            this.executed.blocks++;
+        }
+    }
+}
+
+const WORK_TIME = 0.75;
+
+class RunningStatsView {
+    constructor ({runningStats, maxRecordedTime, dom}) {
+        this.recordedTimeDom =
+            dom.getElementsByClassName('profile-count-amount-recorded')[0];
+        this.stepsLoopedDom =
+            dom.getElementsByClassName('profile-count-steps-looped')[0];
+        this.blocksExecutedDom =
+            dom.getElementsByClassName('profile-count-blocks-executed')[0];
+
+        this.maxRecordedTime = maxRecordedTime;
+        this.maxWorkedTime = maxRecordedTime * WORK_TIME;
+        this.runningStats = runningStats;
+    }
+
+    render () {
+        const {
+            runningStats,
+            recordedTimeDom,
+            stepsLoopedDom,
+            blocksExecutedDom
+        } = this;
+        const {executed} = runningStats;
+        const fractionWorked = runningStats.recordedTime / this.maxWorkedTime;
+        recordedTimeDom.innerText = `${(fractionWorked * 100).toFixed(1)} %`;
+        stepsLoopedDom.innerText = executed.steps;
+        blocksExecutedDom.innerText = executed.blocks;
+    }
+}
+
+class Frames {
+    constructor (profiler) {
+        this.profiler = profiler;
+
+        this.frames = [];
+    }
+
+    update (id, selfTime, totalTime) {
+        if (!this.frames[id]) {
+            this.frames[id] = new StatView(this.profiler.nameById(id));
+        }
+        this.frames[id].update(selfTime, totalTime);
+    }
+}
+
+const frameOrder = [
+    'blockFunction',
+    'execute',
+    'Sequencer.stepThread',
+    'Sequencer.stepThreads#inner',
+    'Sequencer.stepThreads',
+    'RenderWebGL.draw',
+    'Runtime._step'
+];
+
+class FramesTable extends StatTable {
+    constructor (options) {
+        super(options);
+
+        this.profiler = options.profiler;
+        this.frames = options.frames;
+    }
+
+    keys () {
+        const keys = Object.keys(this.frames.frames)
+            .map(id => this.profiler.nameById(Number(id)));
+        keys.sort((a, b) => frameOrder.indexOf(a) - frameOrder.indexOf(b));
+        return keys;
+    }
+
+    viewOf (key) {
+        return this.frames.frames[this.profiler.idByName(key)];
+    }
+
+    isSlow (key, frame) {
+        return ([
+            'Sequencer.stepThreads',
+            'Sequencer.stepThreads#inner',
+            'Sequencer.stepThread',
+            'execute'
+        ].indexOf(key) > 0 &&
+        frame.selfTime / frame.totalTime > SLOW);
+    }
+}
+
+class Opcodes {
+    constructor (profiler) {
+        this.blockFunctionId = profiler.idByName('blockFunction');
+
+        this.opcodes = {};
+    }
+
+    update (id, selfTime, totalTime, arg) {
+        if (id === this.blockFunctionId) {
+            if (!this.opcodes[arg]) {
+                this.opcodes[arg] = new StatView(arg);
+            }
+            this.opcodes[arg].update(selfTime, totalTime);
+        }
+    }
+}
+
+class OpcodeTable extends StatTable {
+    constructor (options) {
+        super(options);
+
+        this.profiler = options.profiler;
+        this.opcodes = options.opcodes;
+        this.frames = options.frames;
+    }
+
+    keys () {
+        const keys = Object.keys(this.opcodes.opcodes);
+        keys.sort();
+        return keys;
+    }
+
+    viewOf (key) {
+        return this.opcodes.opcodes[key];
+    }
+
+    isSlow (key) {
+        const blockFunctionTotalTime = this.frames.frames[this.profiler.idByName('blockFunction')].totalTime;
+        const rowTotalTime = this.opcodes.opcodes[key].totalTime;
+        const percentOfRun = rowTotalTime / blockFunctionTotalTime;
+        return percentOfRun > SLOW;
+    }
+}
+
+class ProfilerRun {
+    constructor ({vm, maxRecordedTime, warmUpTime}) {
+        this.vm = vm;
+        this.maxRecordedTime = maxRecordedTime;
+        this.warmUpTime = warmUpTime;
+
+        vm.runtime.enableProfiling();
+        const profiler = this.profiler = vm.runtime.profiler;
+        vm.runtime.profiler = null;
+
+        const runningStats = this.runningStats = new RunningStats(profiler);
+        const runningStatsView = this.runningStatsView = new RunningStatsView({
+            dom: document.getElementsByClassName('profile-count-group')[0],
+
+            runningStats,
+            maxRecordedTime: 6000
+        });
+
+        const frames = this.frames = new Frames(profiler);
+        this.frameTable = new FramesTable({
+            table: document
+                .getElementsByClassName('profile-count-frame-table')[0]
+                .getElementsByTagName('tbody')[0],
+
+            profiler,
+            frames
+        });
+
+        const opcodes = this.opcodes = new Opcodes(profiler);
+        this.opcodeTable = new OpcodeTable({
+            table: document
+                .getElementsByClassName('profile-count-opcode-table')[0]
+                .getElementsByTagName('tbody')[0],
+
+            profiler,
+            opcodes,
+            frames
+        });
+
+        const stepId = profiler.idByName('Runtime._step');
+        profiler.onFrame = ({id, selfTime, totalTime, arg}) => {
+            if (id === stepId) {
+                runningStatsView.render();
+            }
+            runningStats.update(id, selfTime, totalTime, arg);
+            opcodes.update(id, selfTime, totalTime, arg);
+            frames.update(id, selfTime, totalTime, arg);
+        };
+    }
+
+    run () {
+        loadProject();
+
+        this.vm.on('workspaceUpdate', () => {
+            setTimeout(() => {
+                this.vm.greenFlag();
+            }, 100);
+            setTimeout(() => {
+                this.vm.runtime.profiler = this.profiler;
+            }, 100 + this.warmUpTime);
+            setTimeout(() => {
+                this.vm.stopAll();
+                clearTimeout(this.vm.runtime._steppingInterval);
+                this.vm.runtime.profiler = null;
+
+                this.frameTable.render();
+                this.opcodeTable.render();
+            }, 100 + this.warmUpTime + this.maxRecordedTime);
+        });
+    }
+}
+
+window.onload = function () {
+    // Lots of global variables to make debugging easier
+    // Instantiate the VM.
+    const vm = new window.VirtualMachine();
+    Scratch.vm = vm;
+
+    vm.setTurboMode(true);
+
+    const storage = new ScratchStorage(); /* global ScratchStorage */
+    const AssetType = storage.AssetType;
+    storage.addWebSource([AssetType.Project], getProjectUrl);
+    storage.addWebSource([AssetType.ImageVector, AssetType.ImageBitmap, AssetType.Sound], getAssetUrl);
+    vm.attachStorage(storage);
+
+    new LoadingProgress(progress => {
+        document.getElementsByClassName('loading-total')[0]
+            .innerText = progress.total;
+        document.getElementsByClassName('loading-complete')[0]
+            .innerText = progress.complete;
+    }).on(storage);
+
+    new ProfilerRun({
+        vm,
+        warmUpTime: 4000,
+        maxRecordedTime: 6000
+    }).run();
+
+    // Instantiate the renderer and connect it to the VM.
+    const canvas = document.getElementById('scratch-stage');
+    const renderer = new window.RenderWebGL(canvas);
+    Scratch.renderer = renderer;
+    vm.attachRenderer(renderer);
+    const audioEngine = new window.AudioEngine();
+    vm.attachAudioEngine(audioEngine);
+
+    // Feed mouse events as VM I/O events.
+    document.addEventListener('mousemove', e => {
+        const rect = canvas.getBoundingClientRect();
+        const coordinates = {
+            x: e.clientX - rect.left,
+            y: e.clientY - rect.top,
+            canvasWidth: rect.width,
+            canvasHeight: rect.height
+        };
+        Scratch.vm.postIOData('mouse', coordinates);
+    });
+    canvas.addEventListener('mousedown', e => {
+        const rect = canvas.getBoundingClientRect();
+        const data = {
+            isDown: true,
+            x: e.clientX - rect.left,
+            y: e.clientY - rect.top,
+            canvasWidth: rect.width,
+            canvasHeight: rect.height
+        };
+        Scratch.vm.postIOData('mouse', data);
+        e.preventDefault();
+    });
+    canvas.addEventListener('mouseup', e => {
+        const rect = canvas.getBoundingClientRect();
+        const data = {
+            isDown: false,
+            x: e.clientX - rect.left,
+            y: e.clientY - rect.top,
+            canvasWidth: rect.width,
+            canvasHeight: rect.height
+        };
+        Scratch.vm.postIOData('mouse', data);
+        e.preventDefault();
+    });
+
+    // Feed keyboard events as VM I/O events.
+    document.addEventListener('keydown', e => {
+        // Don't capture keys intended for Blockly inputs.
+        if (e.target !== document && e.target !== document.body) {
+            return;
+        }
+        Scratch.vm.postIOData('keyboard', {
+            keyCode: e.keyCode,
+            isDown: true
+        });
+        e.preventDefault();
+    });
+    document.addEventListener('keyup', e => {
+        // Always capture up events,
+        // even those that have switched to other targets.
+        Scratch.vm.postIOData('keyboard', {
+            keyCode: e.keyCode,
+            isDown: false
+        });
+        // E.g., prevent scroll.
+        if (e.target !== document && e.target !== document.body) {
+            e.preventDefault();
+        }
+    });
+
+    // Run threads
+    vm.start();
+};
diff --git a/src/benchmark/index.html b/src/benchmark/index.html
new file mode 100644
index 000000000..7ddc98dc3
--- /dev/null
+++ b/src/benchmark/index.html
@@ -0,0 +1,69 @@
+<!doctype html>
+
+<html lang="en">
+<head>
+    <meta charset="utf-8">
+    <title>Scratch VM Benchmark</title>
+    <style>
+        canvas {
+          border: 5px solid black;
+        }
+    </style>
+    <link rel="stylesheet" href="./benchmark.css" type="text/css" media="screen">
+</head>
+<body>
+    <h2>Scratch VM Benchmark</h2>
+    <canvas id="scratch-stage" style="width: 480px; height: 360px;"></canvas><br />
+  <div class="loading">
+    <label>Loading:</label>
+    <span class="loading-complete">0</span> / <span class="loading-total">0</span>
+  </div>
+  <div class="profile-count-group">
+    <div class="profile-count">
+      <label>Percent of time worked:</label>
+      <span class="profile-count-value profile-count-amount-recorded">...</span>
+    </div>
+    <div class="profile-count">
+      <label>Steps looped:</label>
+      <span class="profile-count-value profile-count-steps-looped">...</span>
+    </div>
+    <div class="profile-count">
+      <label>Blocks executed:</label>
+      <span class="profile-count-value profile-count-blocks-executed">...</span>
+    </div>
+  </div>
+
+  <div class="profile-tables">
+  <table class="profile-count-frame-table" cellspacing="0">
+    <thead>
+    <tr class="profile-count-frame-head"><th>Frame</th><th>Self Time</th><th>Total Time</th><th>Executions</th></tr>
+    </thead>
+    <tbody>
+    <tr class="profiler-count-running"><td colspan="4"></td></tr>
+    </tbody>
+  </table>
+
+  <table class="profile-count-opcode-table" cellspacing="0">
+    <thead>
+    <tr class="profile-count-opcode-head">
+      <th>opcode</th><th>Self Time</th><th>Total Time</th><th>Executions</th>
+    </tr>
+    </thead>
+    <tbody>
+    <tr class="profiler-count-running"><td colspan="4"></td></tr>
+    </tbody>
+  </table>
+  </div>
+
+  <div id="blocks"></div>
+
+  <!-- FPS counter, Syntax highlighter, Blocks, Renderer -->
+  <script src="../playground/vendor.js"></script>
+  <!-- Storage module -->
+  <script src="../playground/scratch-storage.js"></script>
+  <!-- VM -->
+  <script src="../playground/scratch-vm.js"></script>
+  <!-- Playground -->
+  <script src="./benchmark.js"></script>
+</body>
+</html>
diff --git a/webpack.config.js b/webpack.config.js
index f2d4c880c..6b32c6d83 100644
--- a/webpack.config.js
+++ b/webpack.config.js
@@ -130,5 +130,68 @@ module.exports = [
                 from: 'src/playground'
             }])
         ])
+    }),
+    // Benchmark
+    defaultsDeep({}, base, {
+        target: 'web',
+        entry: {
+            'scratch-vm': './src/index.js',
+            'vendor': [
+                // FPS counter
+                'stats.js/build/stats.min.js',
+                // Syntax highlighter
+                'highlightjs/highlight.pack.min.js',
+                // Scratch Blocks
+                'scratch-blocks/dist/vertical.js',
+                // Audio
+                'scratch-audio',
+                // Renderer
+                'scratch-render'
+            ]
+        },
+        output: {
+            path: path.resolve(__dirname, 'benchmark'),
+            filename: '[name].js'
+        },
+        module: {
+            rules: base.module.rules.concat([
+                {
+                    test: require.resolve('./src/index.js'),
+                    loader: 'expose-loader?VirtualMachine'
+                },
+                {
+                    test: require.resolve('stats.js/build/stats.min.js'),
+                    loader: 'script-loader'
+                },
+                {
+                    test: require.resolve('highlightjs/highlight.pack.min.js'),
+                    loader: 'script-loader'
+                },
+                {
+                    test: require.resolve('scratch-blocks/dist/vertical.js'),
+                    loader: 'expose-loader?Blockly'
+                },
+                {
+                    test: require.resolve('scratch-audio'),
+                    loader: 'expose-loader?AudioEngine'
+                },
+                {
+                    test: require.resolve('scratch-render'),
+                    loader: 'expose-loader?RenderWebGL'
+                }
+            ])
+        },
+        plugins: base.plugins.concat([
+            new CopyWebpackPlugin([{
+                from: 'node_modules/scratch-blocks/media',
+                to: 'media'
+            }, {
+                from: 'node_modules/highlightjs/styles/zenburn.css'
+            }, {
+                from: 'node_modules/scratch-storage/dist/web'
+            }, {
+                from: 'src/benchmark'
+            }])
+        ])
     })
 ];