diff --git a/backend/src/lib/db.ts b/backend/src/lib/db.ts
new file mode 100644
index 0000000..f2542f3
--- /dev/null
+++ b/backend/src/lib/db.ts
@@ -0,0 +1,212 @@
+import Database from 'better-sqlite3';
+import path from 'path';
+import { seedDatabase } from './seed';
+
+const DB_PATH = process.env.DB_PATH || path.join(process.cwd(), 'data', 'zombie_invasion.db');
+
+let db: Database.Database;
+
+export function getDb(): Database.Database {
+  if (!db) {
+    const fs = require('fs');
+    const dir = path.dirname(DB_PATH);
+    if (!fs.existsSync(dir)) {
+      fs.mkdirSync(dir, { recursive: true });
+    }
+    db = new Database(DB_PATH);
+    db.pragma('journal_mode = WAL');
+    db.pragma('foreign_keys = ON');
+    initSchema(db);
+    seedDatabase();
+  }
+  return db;
+}
+
+function initSchema(db: Database.Database) {
+  db.exec(`
+    CREATE TABLE IF NOT EXISTS players (
+      steam_id TEXT PRIMARY KEY,
+      player_name TEXT NOT NULL,
+      profile_level INTEGER DEFAULT 1,
+      free_currency INTEGER DEFAULT 0,
+      donate_currency INTEGER DEFAULT 0,
+      dust_currency INTEGER DEFAULT 0,
+      arcade_pack_credits TEXT DEFAULT '{"standard":0,"premium":0}',
+      sounds_wheel TEXT DEFAULT '{}',
+      created_at TEXT DEFAULT (datetime('now')),
+      updated_at TEXT DEFAULT (datetime('now'))
+    );
+
+    CREATE TABLE IF NOT EXISTS game_sessions (
+      game_id TEXT PRIMARY KEY,
+      match_id INTEGER,
+      session_id TEXT,
+      status TEXT DEFAULT 'active',
+      created_at TEXT DEFAULT (datetime('now'))
+    );
+
+    CREATE TABLE IF NOT EXISTS game_history (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      steam_id TEXT NOT NULL,
+      game_id TEXT,
+      match_id INTEGER,
+      result TEXT,
+      hero TEXT,
+      hero_level INTEGER,
+      difficulty TEXT,
+      duration INTEGER,
+      kills INTEGER DEFAULT 0,
+      deaths INTEGER DEFAULT 0,
+      score INTEGER DEFAULT 0,
+      outgoing_damage REAL DEFAULT 0,
+      incoming_damage REAL DEFAULT 0,
+      items TEXT,
+      modifiers TEXT,
+      aghanim_scepter INTEGER DEFAULT 0,
+      aghanim_shard INTEGER DEFAULT 0,
+      gold_earned INTEGER DEFAULT 0,
+      session_id TEXT,
+      created_at TEXT DEFAULT (datetime('now'))
+    );
+
+    CREATE TABLE IF NOT EXISTS battle_passes (
+      steam_id TEXT PRIMARY KEY,
+      level INTEGER DEFAULT 0,
+      experience INTEGER DEFAULT 0,
+      has_premium INTEGER DEFAULT 0,
+      claimed_rewards TEXT DEFAULT '[]',
+      claimed_premium_rewards TEXT DEFAULT '[]',
+      created_at TEXT DEFAULT (datetime('now')),
+      updated_at TEXT DEFAULT (datetime('now'))
+    );
+
+    CREATE TABLE IF NOT EXISTS battle_pass_quests (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      steam_id TEXT NOT NULL,
+      quest_id TEXT NOT NULL,
+      type TEXT NOT NULL,
+      name TEXT,
+      description TEXT,
+      progress INTEGER DEFAULT 0,
+      target INTEGER DEFAULT 1,
+      completed INTEGER DEFAULT 0,
+      claimed INTEGER DEFAULT 0,
+      reward_exp INTEGER DEFAULT 0,
+      reward_free_currency INTEGER DEFAULT 0,
+      quality TEXT,
+      npc TEXT,
+      target_item TEXT,
+      created_at TEXT DEFAULT (datetime('now')),
+      updated_at TEXT DEFAULT (datetime('now'))
+    );
+
+    CREATE TABLE IF NOT EXISTS purchases (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      steam_id TEXT NOT NULL,
+      item_id TEXT NOT NULL,
+      item_category TEXT,
+      card_id INTEGER,
+      price_free INTEGER DEFAULT 0,
+      price_donate INTEGER DEFAULT 0,
+      price_dust INTEGER DEFAULT 0,
+      created_at TEXT DEFAULT (datetime('now'))
+    );
+
+    CREATE TABLE IF NOT EXISTS active_effects (
+      steam_id TEXT PRIMARY KEY,
+      effects TEXT DEFAULT '{}',
+      updated_at TEXT DEFAULT (datetime('now'))
+    );
+
+    CREATE TABLE IF NOT EXISTS promo_codes (
+      code TEXT PRIMARY KEY,
+      free_currency INTEGER DEFAULT 0,
+      donate_currency INTEGER DEFAULT 0,
+      dust_currency INTEGER DEFAULT 0,
+      max_uses INTEGER DEFAULT 1,
+      current_uses INTEGER DEFAULT 0,
+      expires_at TEXT
+    );
+
+    CREATE TABLE IF NOT EXISTS promo_redemptions (
+      steam_id TEXT,
+      code TEXT,
+      redeemed_at TEXT DEFAULT (datetime('now')),
+      PRIMARY KEY (steam_id, code)
+    );
+
+    CREATE TABLE IF NOT EXISTS card_levels (
+      steam_id TEXT PRIMARY KEY,
+      card_levels TEXT DEFAULT '{}',
+      updated_at TEXT DEFAULT (datetime('now'))
+    );
+
+    CREATE TABLE IF NOT EXISTS decks (
+      steam_id TEXT,
+      deck_index INTEGER,
+      name TEXT DEFAULT 'My Deck',
+      cards TEXT DEFAULT '[]',
+      updated_at TEXT DEFAULT (datetime('now')),
+      PRIMARY KEY (steam_id, deck_index)
+    );
+
+    CREATE TABLE IF NOT EXISTS equipment (
+      steam_id TEXT PRIMARY KEY,
+      equipment TEXT DEFAULT '{}',
+      updated_at TEXT DEFAULT (datetime('now'))
+    );
+
+    CREATE TABLE IF NOT EXISTS arsenal_loadouts (
+      steam_id TEXT,
+      hero_name TEXT,
+      loadout TEXT DEFAULT '{}',
+      updated_at TEXT DEFAULT (datetime('now')),
+      PRIMARY KEY (steam_id, hero_name)
+    );
+
+    CREATE TABLE IF NOT EXISTS arsenal_inventory (
+      steam_id TEXT,
+      instance_id TEXT,
+      item_name TEXT,
+      quality TEXT,
+      upgrade_level INTEGER DEFAULT 0,
+      serial INTEGER,
+      global_serial INTEGER,
+      owner_name TEXT,
+      pinned INTEGER DEFAULT 0,
+      favorite INTEGER DEFAULT 0,
+      stats TEXT DEFAULT '[]',
+      PRIMARY KEY (steam_id, instance_id)
+    );
+
+    CREATE TABLE IF NOT EXISTS arsenal_market_listings (
+      listing_id TEXT PRIMARY KEY,
+      steam_id TEXT NOT NULL,
+      instance_id TEXT,
+      item_name TEXT,
+      quality TEXT,
+      upgrade_level INTEGER DEFAULT 0,
+      serial INTEGER,
+      global_serial INTEGER,
+      price_free INTEGER DEFAULT 0,
+      status TEXT DEFAULT 'active',
+      created_at TEXT DEFAULT (datetime('now'))
+    );
+
+    CREATE TABLE IF NOT EXISTS arsenal_market_sales (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      listing_id TEXT,
+      seller_steam_id TEXT,
+      buyer_steam_id TEXT,
+      item_name TEXT,
+      price_free INTEGER,
+      created_at TEXT DEFAULT (datetime('now'))
+    );
+
+    CREATE TABLE IF NOT EXISTS death_sentence_contracts (
+      steam_id TEXT PRIMARY KEY,
+      contracts TEXT DEFAULT '{}',
+      updated_at TEXT DEFAULT (datetime('now'))
+    );
+  `);
+}
diff --git a/backend/src/lib/seed.ts b/backend/src/lib/seed.ts
new file mode 100644
index 0000000..83aea4f
--- /dev/null
+++ b/backend/src/lib/seed.ts
@@ -0,0 +1,28 @@
+import { getDb } from './db';
+
+export function seedDatabase() {
+  const db = getDb();
+  const count = db.prepare('SELECT COUNT(*) as c FROM promo_codes').get() as { c: number };
+  if (count.c > 0) return;
+
+  const insert = db.prepare(`
+    INSERT INTO promo_codes (code, free_currency, donate_currency, dust_currency, max_uses, expires_at)
+    VALUES (?, ?, ?, ?, ?, ?)
+  `);
+
+  const codes = [
+    ['WELCOME100', 100, 0, 0, 100, null],
+    ['ZOMBIE500', 500, 50, 0, 50, null],
+    ['DONATE100', 0, 100, 0, 20, null],
+    ['DUST250', 0, 0, 250, 30, null],
+  ];
+
+  const tx = db.transaction(() => {
+    for (const c of codes) {
+      insert.run(...c);
+    }
+  });
+  tx();
+
+  console.log('Database seeded with promo codes');
+}