diff --git a/data/db.js b/data/db.js
new file mode 100644
index 0000000..1d5db7e
--- /dev/null
+++ b/data/db.js
@@ -0,0 +1,146 @@
+"use strict";
+
+export default class WbDb extends EventTarget {
+  static get EVENT_CHANGE() { return "change"; }
+
+  static get DB_NAME() { return "watterblock"; }
+  static get DB_NAME_TEST() { return "test-watterblock"; }
+  static get DB_VERSION() { return 1; }
+
+  static get OS_SESSIONS() { return "sessions"; }
+
+  /** Whether the WbDb constructor may be called. */
+  static #mayConstruct = false;
+  /** The single instance of this class.
+   * @type {?WbDb} */
+  static #instance = null;
+
+  constructor(testing, version) {
+    if (!WbDb.#mayConstruct) {
+      throw new TypeError("WbDb may not be constructed externally");
+    }
+    WbDb.#mayConstruct = false;
+
+    super();
+
+    let req = indexedDB.open(
+      testing ? WbDb.DB_NAME_TEST : WbDb.DB_NAME,
+      testing ? version : WbDb.DB_VERSION);
+    req.addEventListener("blocked", this.#handleBlocked.bind(this));
+    req.addEventListener("upgradeneeded", this.#handleUpgrade.bind(this));
+    req.addEventListener("error", this.#handleError.bind(this));
+    req.addEventListener("success", this.#handleSuccess.bind(this));
+  }
+
+  /** Get an instance of `WbDb`.
+   *
+   * If `testing` is `true`, a oneof instance is created, that connects to a
+   * testing database. In that case `version` can be used to set the database
+   * up for a specific version, so it can be tested.
+   *
+   * Otherwise all calls return the same instance.
+   *
+   * @param {boolean=} testing Whether to open a regular or testing connection.
+   * @param {number=} version The version to open a testing connection for.
+   */
+  static get(testing, version) {
+    if (testing) {
+      WbDb.#mayConstruct = true;
+      return new WbDb(true, version ?? WbDb.DB_VERSION);
+    }
+
+    if (WbDb.#instance === null) {
+      WbDb.#mayConstruct = true;
+      WbDb.#instance = new WbDb();
+    }
+
+    return WbDb.#instance;
+  }
+
+  /** The actual IndexedDB.
+   * @type{?IDBDatabase}
+   */
+  #db = null;
+  /** Whether the opening of the DB is currently blocked. */
+  #blocked = false;
+  /** Whether opening the DB has failed. */
+  #failed = false;
+
+  /** Get the actual database. */
+  get db() {
+    if (this.#db === null)
+      throw new Error("WbDb is not yet open");
+
+    return this.#db;
+  }
+
+  /** Shorthand for `WbDb.get().db()`; */
+  static getDb() {
+    return WbDb.get().db();
+  }
+
+  /** Check whether the database opening has been blocked. */
+  get blocked() {
+    return this.#blocked;
+  }
+
+  /** Check whether the database is opened yet. */
+  get open() {
+    return this.#db !== null;
+  }
+
+  /** Check whether opening the database has failed. */
+  get failed() {
+    return this.#failed;
+  }
+
+  /** Handle the `blocked` event for opening the DB.
+   * @param {IDBVersionChangeEvent} event The actual event.
+   */
+  #handleBlocked(event) {
+    this.#blocked = true;
+    this.dispatchEvent(new CustomEvent(WbDb.EVENT_CHANGE));
+  }
+
+  /** Handle the `upgradeneeded` event from opening the DB.
+   * @param {IDBVersionChangeEvent} event The actual event.
+   */
+  #handleUpgrade(event) {
+    let {
+      oldVersion: old,
+      newVersion: now,
+      target: { result: db, transaction: trans },
+    } = event;
+
+    if (old < 1 && now >= 1)
+      this.#version1(db, trans);
+  }
+
+  /** Handle the `error` event from opening the DB.
+   * @param {Event} event The actual event.
+   */
+  #handleError(event) {
+    this.#failed = true;
+    this.dispatchEvent(new CustomEvent(WbDb.EVENT_CHANGE));
+  }
+
+  /** Handle the `success` event from opening the DB.
+   * @param {Event} event The actual event.
+   */
+  #handleSuccess(event) {
+    this.#blocked = false;
+    this.#db = event.target.result;
+    this.dispatchEvent(new CustomEvent(WbDb.EVENT_CHANGE));
+  }
+
+  /** Do the migration for db version 1.
+   * @param {IDBDatabase} db The db to upgrade.
+   * @param {IDBTransaction} trans The db transaction.
+   */
+  #version1(db, trans) {
+    db.createObjectStore(WbDb.OS_SESSIONS, {
+      keyPath: "id",
+      autoIncrement: true,
+    });
+  }
+}
diff --git a/data/db.test.js b/data/db.test.js
new file mode 100644
index 0000000..9ab1039
--- /dev/null
+++ b/data/db.test.js
@@ -0,0 +1,142 @@
+"use strict";
+
+import { Round } from "../models/round.js";
+import WbDb from "./db.js";
+
+/** The instance used for the current test.
+ *
+ * Put test instances of `WbDb` into this variable. If it is used, the
+ * connection is automatically closed after the test is done. That in turn
+ * means that the database can then be deleted immediately, thus speeding up
+ * the next test.
+ *
+ * @type {WbDb}
+ */
+let inst = null;
+
+/** Wait for the `WbDb.EVENT_CHANGE` to be fired on `instance`.
+ *
+ * Uses the `inst` global variable if no `instance` parameter is passed.
+ *
+ * @param {WbDb=} instance The instance to wait on.
+ */
+function waitForChange(instance) {
+  return new Promise(function(resolve) {
+    (instance ?? inst).addEventListener(WbDb.EVENT_CHANGE, function() {
+      resolve();
+    });
+  });
+}
+
+export default function() {
+  QUnit.module("db", function(hooks) {
+
+    // delete test database before each test
+    hooks.beforeEach(function() {
+      return new Promise(function(resolve) {
+        let req = indexedDB.deleteDatabase(WbDb.DB_NAME_TEST);
+        req.onsuccess = function() {
+          resolve();
+        };
+      });
+    });
+
+    hooks.afterEach(function() {
+      if (inst !== null)
+        if (inst.open)
+          inst.db.close();
+      inst = null;
+    });
+
+    QUnit.test.if(
+      "cleanup works",
+      // not yet baseline widely available, should be in November 2026
+      // TODO: check in November 2026, make unconditional if possible then
+      "databases" in indexedDB,
+      async function(assert) {
+        let dbs = await indexedDB.databases();
+        assert.true(
+          dbs.every(({name}) => name !== WbDb.DB_NAME_TEST),
+          "no testing db");
+      });
+
+    QUnit.test("cannot call constructor", function(assert) {
+      assert.throws(function() {
+        new WbDb();
+      });
+
+      assert.throws(function() {
+        new WbDb(true);
+      });
+
+      assert.throws(function() {
+        new WbDb(true, 1);
+      });
+    });
+
+    QUnit.test("open db", async function(assert) {
+      inst = WbDb.get(true);
+      await waitForChange();
+
+      assert.false(inst.blocked, "not blocked");
+      assert.false(inst.failed, "not failed");
+      assert.true(inst.open, "is open");
+      assert.notStrictEqual(inst.db, null, "getting db succeeds");
+      assert.strictEqual(inst.db.version, WbDb.DB_VERSION, "correct version");
+    });
+
+    QUnit.test("opening is blocked", async function(assert) {
+      let first = WbDb.get(true, 1);
+      await waitForChange(first);
+      assert.true(first.open, "first instance opened");
+      assert.strictEqual(first.db.version, 1, "first instance is version 1");
+
+      inst = WbDb.get(true, 2);
+      await waitForChange();
+      assert.true(inst.blocked, "second instance blocked");
+      assert.false(inst.open, "second instance not open");
+      assert.false(inst.failed, "second instance not failed");
+
+      first.db.close();
+      await waitForChange();
+      assert.false(inst.blocked, "second instance not blocked");
+      assert.true(inst.open, "second instance open");
+      assert.false(inst.failed, "second instance not failed");
+      assert.strictEqual(inst.db.version, 2, "second instance is version 2");
+    });
+
+    QUnit.test("opening fails", async function(assert) {
+      let first = WbDb.get(true, 2);
+      await waitForChange(first);
+      assert.true(first.open, "first instance opened");
+      assert.strictEqual(first.db.version, 2, "first instance is version 2");
+      first.db.close();
+
+      let second = WbDb.get(true, 1)
+      await waitForChange(second);
+      if (second.blocked)
+        await waitForChange(second);
+
+      assert.false(second.blocked, "second instance not blocked");
+      assert.false(second.open, "second instance not open");
+      assert.true(second.failed, "second instance failed");
+    });
+
+    QUnit.test("schema version 1", async function(assert) {
+      inst = WbDb.get(true, 1);
+      await waitForChange();
+      assert.true(inst.open, "db is opened");
+      assert.strictEqual(inst.db.version, 1, "db is version 1");
+
+      let osn = inst.db.objectStoreNames;
+      assert.strictEqual(osn.length, 1, "correct number of object stores");
+      assert.true(osn.contains(WbDb.OS_SESSIONS), "contains sessions");
+
+      let trans = inst.db.transaction(osn);
+      let sessions = trans.objectStore(WbDb.OS_SESSIONS);
+      assert.strictEqual(sessions.keyPath, "id", "sessions keyPath");
+      assert.true(sessions.autoIncrement, "sessions autoIncrement");
+      assert.strictEqual(sessions.indexNames.length, 0, "sessions no indexes");
+    });
+  });
+}
diff --git a/test.js b/test.js
index 9311c67..92fb8a4 100644
--- a/test.js
+++ b/test.js
@@ -1,11 +1,19 @@
+"use strict";
+
 import round from "./models/round.test.js";
 import roundResult from "./models/round_result.test.js";
 import game from "./models/game.test.js";
 import session from "./models/session.test.js";
 
+import db from "./data/db.test.js";
+
 QUnit.module("models", function() {
   round();
   roundResult();
   game();
   session();
 });
+
+QUnit.module("data", function() {
+  db();
+});