diff --git a/src/ds/money.test.ts b/src/ds/money.test.ts
new file mode 100644
index 0000000..7ebd34d
--- /dev/null
+++ b/src/ds/money.test.ts
@@ -0,0 +1,14 @@
+import { describe, it, expect, beforeEach } from "vitest";
+import { tugrik, tugrikShort, grouped, tugrikRaw, isHidden, setHidden, MASKED } from "./money";
+
+beforeEach(() => { try { localStorage.clear(); } catch {} });
+
+describe("money", () => {
+  it("groups tugrik", () => expect(tugrik("452200")).toBe("452,200₮"));
+  it("groups digits only", () => expect(grouped("500000")).toBe("500,000"));
+  it("abbreviates millions", () => expect(tugrikShort("1200000")).toBe("1,2сая₮"));
+  it("keeps sub-million as full", () => expect(tugrikShort("900000")).toBe("900,000₮"));
+  it("masks when hidden", () => { setHidden(true); expect(tugrik("100")).toBe(MASKED); });
+  it("raw never masks", () => { setHidden(true); expect(tugrikRaw("100")).toBe("100₮"); });
+  it("isHidden reflects storage", () => { setHidden(true); expect(isHidden()).toBe(true); });
+});
diff --git a/src/ds/money.ts b/src/ds/money.ts
new file mode 100644
index 0000000..747b011
--- /dev/null
+++ b/src/ds/money.ts
@@ -0,0 +1,23 @@
+export const MASKED = "••••••";
+const KEY = "mercury.hideAmounts";
+
+export function isHidden(): boolean {
+  try { return localStorage.getItem(KEY) === "true"; } catch { return false; }
+}
+export function setHidden(b: boolean): void {
+  try { localStorage.setItem(KEY, String(b)); } catch {}
+}
+function num(v: string | number): number {
+  return typeof v === "number" ? v : parseFloat(v || "0") || 0;
+}
+export function grouped(v: string | number): string {
+  return new Intl.NumberFormat("en-US", { maximumFractionDigits: 0 }).format(num(v));
+}
+export function tugrikRaw(v: string | number): string { return `${grouped(v)}₮`; }
+export function tugrikShortRaw(v: string | number): string {
+  const m = num(v) / 1_000_000;
+  if (m >= 1) return `${m.toFixed(1).replace(".", ",")}сая₮`;
+  return tugrikRaw(v);
+}
+export function tugrik(v: string | number): string { return isHidden() ? MASKED : tugrikRaw(v); }
+export function tugrikShort(v: string | number): string { return isHidden() ? MASKED : tugrikShortRaw(v); }
diff --git a/vitest.config.ts b/vitest.config.ts
new file mode 100644
index 0000000..643bb3b
--- /dev/null
+++ b/vitest.config.ts
@@ -0,0 +1,6 @@
+import { defineConfig } from "vitest/config";
+import react from "@vitejs/plugin-react";
+export default defineConfig({
+  plugins: [react()],
+  test: { environment: "jsdom", setupFiles: ["./vitest.setup.ts"], globals: true },
+});
diff --git a/vitest.setup.ts b/vitest.setup.ts
new file mode 100644
index 0000000..2a9307e
--- /dev/null
+++ b/vitest.setup.ts
@@ -0,0 +1,24 @@
+import "@testing-library/jest-dom/vitest";
+
+// Polyfill localStorage for jsdom if not available
+if (typeof localStorage === "undefined") {
+  const store: Record<string, string> = {};
+  (global as any).localStorage = {
+    getItem: (key: string) => store[key] || null,
+    setItem: (key: string, value: string) => {
+      store[key] = String(value);
+    },
+    removeItem: (key: string) => {
+      delete store[key];
+    },
+    clear: () => {
+      for (const key in store) {
+        delete store[key];
+      }
+    },
+    key: (index: number) => Object.keys(store)[index] || null,
+    get length() {
+      return Object.keys(store).length;
+    },
+  };
+}