diff --git a/web/server/__tests__/db.test.js b/web/server/__tests__/db.test.js
new file mode 100644
index 0000000..1d0a578
--- /dev/null
+++ b/web/server/__tests__/db.test.js
@@ -0,0 +1,250 @@
+/**
+ * Tests for the Inventory Manager database layer (db.js).
+ *
+ * Uses a temporary on-disk SQLite file per test to exercise real SQL
+ * without touching production data.  The DB_PATH env var is set BEFORE
+ * the dynamic import so better-sqlite3 opens the right file.
+ */
+
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import fs from 'fs';
+import os from 'os';
+import path from 'path';
+
+// ── helpers ────────────────────────────────────────────────────────────
+
+/** Create a fresh temp DB path and set the env var before importing db.js */
+async function createTestDb() {
+  const tmp = path.join(os.tmpdir(), `inv-test-${Date.now()}-${Math.random().toString(36).slice(2)}.db`);
+  process.env.DB_PATH = tmp;
+
+  // Use a cache-buster query string so Node gives us a fresh module
+  const mod = await import(`../db.js?t=${Date.now()}-${Math.random()}`);
+  return { mod, tmp };
+}
+
+function cleanup(tmp) {
+  try { fs.unlinkSync(tmp); } catch { /* ignore */ }
+  try { fs.unlinkSync(tmp + '-wal'); } catch { /* ignore */ }
+  try { fs.unlinkSync(tmp + '-shm'); } catch { /* ignore */ }
+}
+
+// ── tests ──────────────────────────────────────────────────────────────
+
+describe('db – item persistence', () => {
+  let db, tmp;
+
+  beforeEach(async () => {
+    ({ mod: db, tmp } = await createTestDb());
+  });
+
+  afterEach(() => {
+    try { db.closeDb(); } catch { /* already closed */ }
+    cleanup(tmp);
+  });
+
+  it('saveItems + loadItems round-trips item data', () => {
+    const items = [
+      { name: 'minecraft:diamond', count: 64, displayName: 'Diamond' },
+      { name: 'minecraft:iron_ingot', count: 128, displayName: 'Iron Ingot' },
+    ];
+    db.saveItems(items);
+
+    const loaded = db.loadItems();
+    expect(loaded).toHaveLength(2);
+
+    // loadItems returns ORDER BY count DESC
+    expect(loaded[0].name).toBe('minecraft:iron_ingot');
+    expect(loaded[0].count).toBe(128);
+    expect(loaded[1].name).toBe('minecraft:diamond');
+    expect(loaded[1].count).toBe(64);
+  });
+
+  it('saveItems upserts — updates existing rows instead of duplicating', () => {
+    db.saveItems([{ name: 'minecraft:diamond', count: 10, displayName: 'Diamond' }]);
+    db.saveItems([{ name: 'minecraft:diamond', count: 99, displayName: 'Diamond' }]);
+
+    const loaded = db.loadItems();
+    expect(loaded).toHaveLength(1);
+    expect(loaded[0].count).toBe(99);
+  });
+});
+
+describe('db – state key-value store', () => {
+  let db, tmp;
+
+  beforeEach(async () => {
+    ({ mod: db, tmp } = await createTestDb());
+  });
+
+  afterEach(() => {
+    try { db.closeDb(); } catch { /* already closed */ }
+    cleanup(tmp);
+  });
+
+  it('saveState + loadState round-trips JSON', () => {
+    db.saveState('smeltingPaused', true);
+    expect(db.loadState('smeltingPaused')).toBe(true);
+
+    db.saveState('disabledRecipes', { 'minecraft:iron_ingot': true });
+    expect(db.loadState('disabledRecipes')).toEqual({ 'minecraft:iron_ingot': true });
+  });
+
+  it('loadState returns defaultValue when key missing', () => {
+    expect(db.loadState('nonexistent', 42)).toBe(42);
+    expect(db.loadState('nonexistent')).toBeNull();
+  });
+});
+
+describe('db – furnace persistence', () => {
+  let db, tmp;
+
+  beforeEach(async () => {
+    ({ mod: db, tmp } = await createTestDb());
+  });
+
+  afterEach(() => {
+    try { db.closeDb(); } catch { /* already closed */ }
+    cleanup(tmp);
+  });
+
+  it('saveFurnaces + loadFurnaces round-trips furnace status', () => {
+    const furnaces = {
+      'minecraft:furnace_0': {
+        active: true,
+        type: 'minecraft:furnace',
+        input: { name: 'minecraft:raw_iron', count: 8 },
+        fuel: { name: 'minecraft:coal', count: 3 },
+        output: null,
+      },
+    };
+
+    db.saveFurnaces(furnaces);
+    const loaded = db.loadFurnaces();
+
+    expect(loaded['minecraft:furnace_0']).toBeDefined();
+    expect(loaded['minecraft:furnace_0'].active).toBe(true);
+    expect(loaded['minecraft:furnace_0'].input.name).toBe('minecraft:raw_iron');
+  });
+});
+
+describe('db – alert persistence', () => {
+  let db, tmp;
+
+  beforeEach(async () => {
+    ({ mod: db, tmp } = await createTestDb());
+  });
+
+  afterEach(() => {
+    try { db.closeDb(); } catch { /* already closed */ }
+    cleanup(tmp);
+  });
+
+  it('saveAlerts + loadAlerts round-trips triggered alerts', () => {
+    db.saveAlerts([
+      { item: 'minecraft:diamond', triggered: true, current: 5, threshold: 10 },
+      { item: 'minecraft:coal', triggered: false, current: 200, threshold: 50 },
+    ]);
+
+    const loaded = db.loadAlerts();
+    // loadAlerts only returns triggered=1
+    expect(loaded).toHaveLength(1);
+    expect(loaded[0].item).toBe('minecraft:diamond');
+    expect(loaded[0].triggered).toBe(true);
+    expect(loaded[0].current).toBe(5);
+    expect(loaded[0].threshold).toBe(10);
+  });
+});
+
+describe('db – item history', () => {
+  let db, tmp;
+
+  beforeEach(async () => {
+    ({ mod: db, tmp } = await createTestDb());
+  });
+
+  afterEach(() => {
+    try { db.closeDb(); } catch { /* already closed */ }
+    cleanup(tmp);
+  });
+
+  it('getHistory returns recorded snapshots ordered newest-first', () => {
+    // recordItemHistory is throttled (5-min internal cooldown), so we
+    // call it twice — first call records, second is throttled.
+    db.recordItemHistory([
+      { name: 'minecraft:diamond', count: 64 },
+      { name: 'minecraft:iron_ingot', count: 128 },
+    ]);
+
+    const history = db.getHistory('minecraft:diamond', 10);
+    expect(history.length).toBeGreaterThanOrEqual(1);
+    expect(history[0].count).toBe(64);
+  });
+
+  it('getHistorySummary groups by timestamp', () => {
+    db.recordItemHistory([
+      { name: 'a', count: 10 },
+      { name: 'b', count: 20 },
+    ]);
+
+    const summary = db.getHistorySummary();
+    expect(summary.length).toBeGreaterThanOrEqual(1);
+    expect(summary[0].total).toBe(30); // 10 + 20
+  });
+});
+
+describe('db – full state round-trip', () => {
+  let db, tmp;
+
+  beforeEach(async () => {
+    ({ mod: db, tmp } = await createTestDb());
+  });
+
+  afterEach(() => {
+    try { db.closeDb(); } catch { /* already closed */ }
+    cleanup(tmp);
+  });
+
+  it('saveFullState + flushPendingSave + loadFullState restores everything', () => {
+    const state = {
+      inventoryState: {
+        itemList: [
+          { name: 'minecraft:diamond', count: 64, displayName: 'Diamond' },
+        ],
+        grandTotal: 64,
+        chestCount: 2,
+        totalSlots: 54,
+        usedSlots: 1,
+        freeSlots: 53,
+        usedRatio: 0.02,
+        dropperOk: true,
+        barrelOk: false,
+        furnaceCount: 1,
+        furnaceStatus: {
+          'furnace_0': { active: false, type: 'minecraft:furnace', input: null, fuel: null, output: null },
+        },
+        droppers: ['dropper_0'],
+      },
+      activityState: { lastScan: 12345 },
+      alertsState: [{ item: 'minecraft:coal', triggered: true, current: 3, threshold: 10 }],
+      smeltingPaused: false,
+      disabledRecipes: { 'minecraft:charcoal': true },
+      smeltableRecipes: { 'minecraft:raw_iron': 'minecraft:iron_ingot' },
+      craftableRecipes: [{ output: 'minecraft:chest', count: 1, slots: { 1: 'minecraft:planks' } }],
+      craftTurtleOk: true,
+    };
+
+    db.saveFullState(state);
+    db.flushPendingSave(); // force the debounced write
+
+    const restored = db.loadFullState();
+    expect(restored.inventoryState.itemList).toHaveLength(1);
+    expect(restored.inventoryState.itemList[0].name).toBe('minecraft:diamond');
+    expect(restored.inventoryState.grandTotal).toBe(64);
+    expect(restored.smeltingPaused).toBe(false);
+    expect(restored.disabledRecipes).toEqual({ 'minecraft:charcoal': true });
+    expect(restored.craftTurtleOk).toBe(true);
+    expect(restored.alertsState).toHaveLength(1);
+    expect(restored.alertsState[0].item).toBe('minecraft:coal');
+  });
+});