diff --git a/emu.js b/emu.js
index ad4488a..4c93c6b 100644
--- a/emu.js
+++ b/emu.js
@@ -51,6 +51,19 @@ class Emulator {
 		document.addEventListener('keydown', (e) => this.handle_keydown(e));
 		window.addEventListener('resize', () => this.handle_resize());
 
+		this.prof = new Worker("prof.js");
+		this.prof.onmessage = (e) => {
+			const blob = new Blob(
+				[JSON.stringify(e.data)],
+				{ type: "application/json" });
+			const url = URL.createObjectURL(blob);
+			const a = document.createElement("a");
+			a.href = url;
+			a.download = "wipforth-profile.json";
+			a.click();
+			URL.revokeObjectURL(url);
+		};
+
 		this.print("Assembling kernel ");
 		const dots = setInterval(() => this.print("."), DOT_INTERVAL_MS);
 		this.worker = new Worker('boot.js', { type: 'module' });
@@ -59,6 +72,7 @@ class Emulator {
 			clearInterval(dots);
 			this.print(" done\n");
 			this.worker.postMessage({ type: "boot" });
+			this.prof.postMessage({ type: "start", mem: this.mem });
 		};
 
 		fetch('prelude.f')
@@ -85,6 +99,7 @@ class Emulator {
 		if (!this.input_enable) {
 			const sysready = Atomics.load(this.mem_u8, SYSREADY);
 			if (sysready != 0) {
+				this.prof.postMessage({ type: "stop" });
 				this.input_enable = true;
 				this.flush_output();
 				document.getElementById('cursor').classList.add('blinking');