diff --git a/frontend/src/__tests__/AccuracyTracker.test.ts b/frontend/src/__tests__/AccuracyTracker.test.ts
new file mode 100644
index 0000000..d9823c0
--- /dev/null
+++ b/frontend/src/__tests__/AccuracyTracker.test.ts
@@ -0,0 +1,256 @@
+import { describe, it, expect, beforeEach, afterEach } from "vitest";
+import bus from "../engine/EventBus";
+import { accuracyTracker } from "../engine/AccuracyTracker";
+import type { NoteEvent } from "../../../shared/types/MusicData";
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+function makeNote(
+  id: string,
+  midi: number,
+  hand: "left" | "right" | "unknown" = "right"
+): NoteEvent {
+  return {
+    id,
+    midi,
+    pitch: "C4",
+    startTick: 0,
+    durationTick: 480,
+    startSeconds: 0,
+    endSeconds: 1,
+    hand,
+    finger: null,
+    velocity: 80,
+    channel: 0,
+  };
+}
+
+type AccuracyUpdate = { correct: number; wrong: number; missed: number; score: number };
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+describe("AccuracyTracker", () => {
+  let updates: AccuracyUpdate[] = [];
+
+  const listener = (data: AccuracyUpdate) => {
+    updates.push(data);
+  };
+
+  beforeEach(() => {
+    updates = [];
+    bus.on("accuracy:update", listener);
+    accuracyTracker.enable(true);
+    accuracyTracker.reset();
+  });
+
+  afterEach(() => {
+    bus.off("accuracy:update", listener);
+    accuracyTracker.enable(false);
+  });
+
+  // ── Initial state ─────────────────────────────────────────────────────────
+
+  it("starts with score 0 and no counts", () => {
+    expect(accuracyTracker.score).toBe(0);
+  });
+
+  // ── Correct hit ───────────────────────────────────────────────────────────
+
+  it("records a correct hit when input arrives within the window", () => {
+    const note = makeNote("n1", 60);
+    bus.emit("note:on", note);
+    bus.emit("input:note:on", { midi: 60, velocity: 80 });
+
+    const last = updates[updates.length - 1];
+    expect(last.correct).toBe(1);
+    expect(last.wrong).toBe(0);
+    expect(last.missed).toBe(0);
+    expect(last.score).toBe(100);
+  });
+
+  it("score is 100 after a single correct hit", () => {
+    const note = makeNote("n1", 60);
+    bus.emit("note:on", note);
+    bus.emit("input:note:on", { midi: 60, velocity: 80 });
+
+    expect(accuracyTracker.score).toBe(100);
+  });
+
+  // ── Miss ─────────────────────────────────────────────────────────────────
+
+  it("records a miss when note:off fires without any input", () => {
+    const note = makeNote("n1", 60);
+    bus.emit("note:on", note);
+    bus.emit("note:off", note);
+
+    const last = updates[updates.length - 1];
+    expect(last.missed).toBe(1);
+    expect(last.correct).toBe(0);
+    expect(last.score).toBe(0);
+  });
+
+  it("ignores note:off for a note that was already hit", () => {
+    const note = makeNote("n1", 60);
+    bus.emit("note:on", note);
+    bus.emit("input:note:on", { midi: 60, velocity: 80 }); // correct hit
+    const countBefore = updates.length;
+    bus.emit("note:off", note); // already hit — should not emit again
+
+    // No new accuracy:update should have been emitted for the note:off
+    expect(updates.length).toBe(countBefore);
+    const last = updates[updates.length - 1];
+    expect(last.missed).toBe(0);
+  });
+
+  // ── Wrong ─────────────────────────────────────────────────────────────────
+
+  it("records wrong when input MIDI does not match any pending note", () => {
+    const note = makeNote("n1", 60);
+    bus.emit("note:on", note);
+    bus.emit("input:note:on", { midi: 61, velocity: 80 }); // wrong key
+
+    const last = updates[updates.length - 1];
+    expect(last.wrong).toBe(1);
+    expect(last.correct).toBe(0);
+  });
+
+  it("records wrong when no notes are pending at all", () => {
+    bus.emit("input:note:on", { midi: 60, velocity: 80 });
+
+    const last = updates[updates.length - 1];
+    expect(last.wrong).toBe(1);
+  });
+
+  it("second input for the same already-hit note counts as wrong", () => {
+    const note = makeNote("n1", 60);
+    bus.emit("note:on", note);
+    bus.emit("input:note:on", { midi: 60, velocity: 80 }); // correct
+    bus.emit("input:note:on", { midi: 60, velocity: 80 }); // note already marked hit → wrong
+
+    const last = updates[updates.length - 1];
+    expect(last.correct).toBe(1);
+    expect(last.wrong).toBe(1);
+  });
+
+  // ── Score formula ─────────────────────────────────────────────────────────
+
+  it("score = correct / total * 100, rounded", () => {
+    // 2 correct + 1 wrong + 1 missed = 4 total → 50%
+    const n1 = makeNote("n1", 60);
+    const n2 = makeNote("n2", 62);
+    const n3 = makeNote("n3", 64);
+
+    bus.emit("note:on", n1);
+    bus.emit("input:note:on", { midi: 60, velocity: 80 }); // correct
+
+    bus.emit("note:on", n2);
+    bus.emit("input:note:on", { midi: 62, velocity: 80 }); // correct
+
+    bus.emit("note:on", n3);
+    bus.emit("note:off", n3); // missed
+
+    bus.emit("input:note:on", { midi: 99, velocity: 80 }); // wrong (no pending note)
+
+    const last = updates[updates.length - 1];
+    expect(last.correct).toBe(2);
+    expect(last.missed).toBe(1);
+    expect(last.wrong).toBe(1);
+    expect(last.score).toBe(50);
+  });
+
+  it("score rounds to nearest integer", () => {
+    // 2 correct + 1 wrong = 3 total → 66.67% → rounds to 67
+    const n1 = makeNote("n1", 60);
+    const n2 = makeNote("n2", 62);
+
+    bus.emit("note:on", n1);
+    bus.emit("input:note:on", { midi: 60, velocity: 80 }); // correct
+
+    bus.emit("note:on", n2);
+    bus.emit("input:note:on", { midi: 62, velocity: 80 }); // correct
+
+    bus.emit("input:note:on", { midi: 99, velocity: 80 }); // wrong
+
+    expect(accuracyTracker.score).toBe(67);
+  });
+
+  // ── Multiple simultaneous pending notes ───────────────────────────────────
+
+  it("hits the correct note among multiple simultaneously pending notes", () => {
+    const c = makeNote("n1", 60);
+    const e = makeNote("n2", 64);
+    const g = makeNote("n3", 67);
+
+    bus.emit("note:on", c);
+    bus.emit("note:on", e);
+    bus.emit("note:on", g);
+
+    bus.emit("input:note:on", { midi: 64, velocity: 80 }); // hits E
+    bus.emit("input:note:on", { midi: 60, velocity: 80 }); // hits C
+    bus.emit("note:off", g); // G not played → missed
+
+    const last = updates[updates.length - 1];
+    expect(last.correct).toBe(2);
+    expect(last.missed).toBe(1);
+    expect(last.wrong).toBe(0);
+  });
+
+  // ── Reset ─────────────────────────────────────────────────────────────────
+
+  it("reset clears all counts and emits zeros", () => {
+    const note = makeNote("n1", 60);
+    bus.emit("note:on", note);
+    bus.emit("note:off", note); // missed
+
+    accuracyTracker.reset();
+
+    const last = updates[updates.length - 1];
+    expect(last.correct).toBe(0);
+    expect(last.wrong).toBe(0);
+    expect(last.missed).toBe(0);
+    expect(last.score).toBe(0);
+    expect(accuracyTracker.score).toBe(0);
+  });
+
+  // ── Disabled ─────────────────────────────────────────────────────────────
+
+  it("emits nothing and records nothing when disabled", () => {
+    accuracyTracker.enable(false);
+    const countBefore = updates.length;
+
+    const note = makeNote("n1", 60);
+    bus.emit("note:on", note);
+    bus.emit("input:note:on", { midi: 60, velocity: 80 });
+    bus.emit("note:off", note);
+
+    expect(updates.length).toBe(countBefore);
+    expect(accuracyTracker.score).toBe(0);
+  });
+
+  // ── Transport events ──────────────────────────────────────────────────────
+
+  it("resets when transport stops", () => {
+    const note = makeNote("n1", 60);
+    bus.emit("note:on", note);
+    bus.emit("note:off", note); // missed → score 0%
+
+    bus.emit("transport:stateChange", { status: "stopped", seconds: 0 });
+
+    expect(accuracyTracker.score).toBe(0);
+    const last = updates[updates.length - 1];
+    expect(last.missed).toBe(0);
+  });
+
+  it("seek clears pending notes so subsequent note:off does not count as missed", () => {
+    const note = makeNote("n1", 60);
+    bus.emit("note:on", note); // enters pending
+    bus.emit("transport:seek", { seconds: 5 }); // clears pending
+
+    const countBefore = updates.length;
+    bus.emit("note:off", note); // pending was cleared — should be a no-op
+
+    // No new accuracy:update should have fired
+    expect(updates.length).toBe(countBefore);
+    expect(accuracyTracker.score).toBe(0);
+  });
+});
diff --git a/frontend/src/__tests__/MidiClock.test.ts b/frontend/src/__tests__/MidiClock.test.ts
new file mode 100644
index 0000000..f48a15f
--- /dev/null
+++ b/frontend/src/__tests__/MidiClock.test.ts
@@ -0,0 +1,151 @@
+/**
+ * MidiClock tests
+ *
+ * MidiClock's core job is to track "doc-time" (song position in seconds)
+ * using this formula:
+ *
+ *   currentSeconds = _startOffset + Tone.getTransport().seconds * tempoMultiplier
+ *
+ * We mock Tone.js so we can control Transport.seconds without a real audio context.
+ */
+import { describe, it, expect, beforeEach, vi } from "vitest";
+
+// ── Tone.js mock ──────────────────────────────────────────────────────────────
+// vi.hoisted() runs before module-level code so the value is available inside
+// the vi.mock factory despite vi.mock being hoisted to the top of the file.
+
+const mockTransport = vi.hoisted(() => ({
+  seconds: 0,
+  bpm: { value: 120 },
+  state: "stopped" as "started" | "stopped" | "paused",
+  cancel: vi.fn(),
+  start: vi.fn(),
+  pause: vi.fn(),
+  stop: vi.fn(),
+  scheduleRepeat: vi.fn(),
+  scheduleOnce: vi.fn(),
+}));
+
+vi.mock("tone", () => ({
+  getTransport: () => mockTransport,
+  start: vi.fn().mockResolvedValue(undefined),
+}));
+
+import { MidiClock } from "../engine/MidiClock";
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+describe("MidiClock", () => {
+  let clock: MidiClock;
+
+  beforeEach(() => {
+    mockTransport.seconds = 0;
+    mockTransport.cancel.mockClear();
+    mockTransport.scheduleRepeat.mockClear();
+    clock = new MidiClock();
+  });
+
+  // ── currentSeconds formula ────────────────────────────────────────────────
+
+  it("returns 0 on creation (no offset, no transport time)", () => {
+    expect(clock.currentSeconds).toBe(0);
+  });
+
+  it("currentSeconds = startOffset + transport.seconds * multiplier", () => {
+    clock.seek(2); // _startOffset = 2, transport.seconds = 0
+    mockTransport.seconds = 3;
+    // 2 + 3 * 1.0 = 5
+    expect(clock.currentSeconds).toBe(5);
+  });
+
+  it("applies tempoMultiplier to transport.seconds", () => {
+    clock.seek(0);
+    mockTransport.seconds = 4;
+    clock.tempoMultiplier = 0.5;
+    // After setting multiplier, _startOffset is recomputed to preserve currentSeconds.
+    // currentSeconds before set = 0 + 4*1 = 4; after set: offset = 4 - 4*0.5 = 2
+    // currentSeconds after = 2 + 4*0.5 = 4
+    expect(clock.currentSeconds).toBeCloseTo(4);
+  });
+
+  // ── seek ─────────────────────────────────────────────────────────────────
+
+  it("seek sets startOffset and resets transport.seconds to 0", () => {
+    mockTransport.seconds = 10;
+    clock.seek(5);
+    expect(mockTransport.seconds).toBe(0);
+    expect(clock.currentSeconds).toBe(5);
+  });
+
+  it("seek to 0 resets position to start", () => {
+    clock.seek(30);
+    clock.seek(0);
+    expect(clock.currentSeconds).toBe(0);
+  });
+
+  // ── tempoMultiplier ───────────────────────────────────────────────────────
+
+  describe("tempoMultiplier", () => {
+    it("defaults to 1.0", () => {
+      expect(clock.tempoMultiplier).toBe(1.0);
+    });
+
+    it("clamps values below 0.25 to 0.25", () => {
+      clock.tempoMultiplier = 0.1;
+      expect(clock.tempoMultiplier).toBe(0.25);
+    });
+
+    it("clamps values above 2.0 to 2.0", () => {
+      clock.tempoMultiplier = 5.0;
+      expect(clock.tempoMultiplier).toBe(2.0);
+    });
+
+    it("accepts boundary value 0.25", () => {
+      clock.tempoMultiplier = 0.25;
+      expect(clock.tempoMultiplier).toBe(0.25);
+    });
+
+    it("accepts boundary value 2.0", () => {
+      clock.tempoMultiplier = 2.0;
+      expect(clock.tempoMultiplier).toBe(2.0);
+    });
+
+    it("preserves currentSeconds when multiplier changes (no time jump)", () => {
+      // Set a known position: offset=3, transport=2 → currentSeconds=5
+      clock.seek(3);
+      mockTransport.seconds = 2;
+      expect(clock.currentSeconds).toBe(5);
+
+      // Change multiplier — currentSeconds must remain 5
+      clock.tempoMultiplier = 0.5;
+      expect(clock.currentSeconds).toBeCloseTo(5);
+    });
+
+    it("preserves currentSeconds when multiplier increases", () => {
+      clock.seek(1);
+      mockTransport.seconds = 4;
+      // currentSeconds = 1 + 4*1 = 5
+      clock.tempoMultiplier = 2.0;
+      // _startOffset = 5 - 4*2 = -3; currentSeconds = -3 + 4*2 = 5
+      expect(clock.currentSeconds).toBeCloseTo(5);
+    });
+  });
+
+  // ── reschedule ────────────────────────────────────────────────────────────
+
+  it("reschedule resets transport.seconds and re-registers the tick callback", () => {
+    clock.reschedule(7);
+    expect(mockTransport.seconds).toBe(0);
+    expect(mockTransport.scheduleRepeat).toHaveBeenCalledOnce();
+    expect(clock.currentSeconds).toBe(7);
+  });
+
+  // ── state ─────────────────────────────────────────────────────────────────
+
+  it("state reflects the mock transport state", () => {
+    mockTransport.state = "paused";
+    expect(clock.state).toBe("paused");
+    mockTransport.state = "started";
+    expect(clock.state).toBe("started");
+  });
+});