diff --git a/apps/cyberstorm-remix/public/cyberstorm-static/scripts/beta-switch.js b/apps/cyberstorm-remix/public/cyberstorm-static/scripts/beta-switch.js
index ee575756a..2d28ecdfb 100644
--- a/apps/cyberstorm-remix/public/cyberstorm-static/scripts/beta-switch.js
+++ b/apps/cyberstorm-remix/public/cyberstorm-static/scripts/beta-switch.js
@@ -1,39 +1,3 @@
-const legacyProd = {
-  protocol: "https://",
-  hostname: "thunderstore.io",
-  port: "",
-  tld: "io",
-};
-const betaProd = {
-  protocol: "https://",
-  hostname: "new.thunderstore.io",
-  port: "",
-  tld: "io",
-};
-const legacyQA = {
-  protocol: "https://",
-  hostname: "thunderstore.dev",
-  port: "",
-  tld: "dev",
-};
-const betaQA = {
-  protocol: "https://",
-  hostname: "new.thunderstore.dev",
-  port: "",
-  tld: "dev",
-};
-const legacyDev = {
-  protocol: "http://",
-  hostname: "thunderstore.temp",
-  port: "",
-  tld: "temp",
-};
-const betaDev = {
-  protocol: "http://",
-  hostname: "new.thunderstore.temp",
-  port: "",
-  tld: "temp",
-};
 async function checkBetaRedirect(legacy, beta, goToBetaRoR2) {
   const legacyOnlyPages = [
     "/settings",
@@ -124,25 +88,79 @@ async function insertSwitchButton(legacy, beta) {
     }
   }
 }
-const legacy = window.location.hostname.endsWith(legacyProd.tld)
-  ? legacyProd
-  : window.location.hostname.endsWith(legacyQA.tld)
-    ? legacyQA
-    : legacyDev;
-const beta = window.location.hostname.endsWith(betaProd.tld)
-  ? betaProd
-  : window.location.hostname.endsWith(betaQA.tld)
-    ? betaQA
-    : betaDev;
-async function insertSwitchButtonListener() {
-  insertSwitchButton(legacy, beta);
-  document.removeEventListener("DOMContentLoaded", insertSwitchButtonListener);
+function hasBrowserGlobals() {
+  return typeof window !== "undefined" && typeof document !== "undefined";
 }
-if (
-  document.readyState === "complete" ||
-  document.readyState === "interactive"
-) {
-  insertSwitchButton(legacy, beta);
-} else {
-  document.addEventListener("DOMContentLoaded", insertSwitchButtonListener);
+export function initBetaSwitch() {
+  if (!hasBrowserGlobals()) {
+    return;
+  }
+  const globalWindow = window;
+  const initFlag = "__thunderstore_beta_switch_initialized__";
+  if (globalWindow[initFlag]) {
+    return;
+  }
+  globalWindow[initFlag] = true;
+  const legacyProd = {
+    protocol: "https://",
+    hostname: "thunderstore.io",
+    port: "",
+    tld: "io",
+  };
+  const betaProd = {
+    protocol: "https://",
+    hostname: "new.thunderstore.io",
+    port: "",
+    tld: "io",
+  };
+  const legacyQA = {
+    protocol: "https://",
+    hostname: "thunderstore.dev",
+    port: "",
+    tld: "dev",
+  };
+  const betaQA = {
+    protocol: "https://",
+    hostname: "new.thunderstore.dev",
+    port: "",
+    tld: "dev",
+  };
+  const legacyDev = {
+    protocol: "http://",
+    hostname: "thunderstore.localhost",
+    port: "",
+    tld: "localhost",
+  };
+  const betaDev = {
+    protocol: "http://",
+    hostname: "new.thunderstore.localhost",
+    port: "",
+    tld: "localhost",
+  };
+  const legacy = window.location.hostname.endsWith(legacyProd.tld)
+    ? legacyProd
+    : window.location.hostname.endsWith(legacyQA.tld)
+      ? legacyQA
+      : legacyDev;
+  const beta = window.location.hostname.endsWith(betaProd.tld)
+    ? betaProd
+    : window.location.hostname.endsWith(betaQA.tld)
+      ? betaQA
+      : betaDev;
+  async function insertSwitchButtonListener() {
+    insertSwitchButton(legacy, beta);
+    document.removeEventListener(
+      "DOMContentLoaded",
+      insertSwitchButtonListener
+    );
+  }
+  if (
+    document.readyState === "complete" ||
+    document.readyState === "interactive"
+  ) {
+    insertSwitchButton(legacy, beta);
+  } else {
+    document.addEventListener("DOMContentLoaded", insertSwitchButtonListener);
+  }
 }
+initBetaSwitch();
diff --git a/packages/beta-switch/src/__tests__/beta-switch.test.ts b/packages/beta-switch/src/__tests__/beta-switch.test.ts
new file mode 100644
index 000000000..e49b31edd
--- /dev/null
+++ b/packages/beta-switch/src/__tests__/beta-switch.test.ts
@@ -0,0 +1,95 @@
+import { describe, expect, it, vi } from "vitest";
+
+type TestWindow = {
+  location: {
+    hostname: string;
+    pathname: string;
+    assign: (url: string) => void;
+  };
+};
+
+type TestElement = {
+  tag: string;
+  attributes: Map<string, string>;
+  setAttribute: (key: string, value: string) => void;
+  onclick?: (() => void) | null;
+  innerHTML: string;
+  cloneNode: (deep?: boolean) => TestElement;
+};
+
+type TestDocument = {
+  readyState: "complete" | "interactive" | "loading";
+  createElement: (tag: string) => TestElement;
+  addEventListener: (type: string, listener: () => void) => void;
+  removeEventListener: (type: string, listener: () => void) => void;
+  querySelector: (
+    selector: string
+  ) => { appendChild: (child: TestElement) => void } | null;
+};
+
+describe("@thunderstore/beta-switch", () => {
+  it("can be imported without window/document (SSR-safe)", async () => {
+    // Ensure SSR-like environment
+    const g = globalThis as unknown as { window?: unknown; document?: unknown };
+    delete g.window;
+    delete g.document;
+
+    await expect(import("../index")).resolves.toBeTruthy();
+  });
+
+  it("inserts switch button into #nimbusBeta when container exists", async () => {
+    const appended: TestElement[] = [];
+
+    const desktopContainer = {
+      appendChild: (child: TestElement) => appended.push(child),
+    };
+
+    const createElement = (tag: string) => {
+      const element: TestElement = {
+        tag,
+        attributes: new Map<string, string>(),
+        setAttribute: (k: string, v: string) => element.attributes.set(k, v),
+        onclick: undefined,
+        innerHTML: "",
+        cloneNode: () => ({
+          ...element,
+          attributes: new Map(element.attributes),
+        }),
+      };
+      return element;
+    };
+
+    const addEventListener = vi.fn();
+    const removeEventListener = vi.fn();
+
+    const g = globalThis as unknown as { window?: unknown; document?: unknown };
+
+    const w: TestWindow = {
+      location: {
+        hostname: "thunderstore.temp",
+        pathname: "/",
+        assign: vi.fn(),
+      },
+    };
+
+    const d: TestDocument = {
+      readyState: "complete",
+      createElement,
+      addEventListener:
+        addEventListener as unknown as TestDocument["addEventListener"],
+      removeEventListener:
+        removeEventListener as unknown as TestDocument["removeEventListener"],
+      querySelector: (selector: string) =>
+        selector === "#nimbusBeta" ? desktopContainer : null,
+    };
+
+    g.window = w;
+    g.document = d;
+
+    const mod: typeof import("../index") = await import("../index");
+    mod.initBetaSwitch();
+
+    expect(appended.length).toBe(1);
+    expect(appended[0].tag).toBe("button");
+  });
+});
diff --git a/packages/beta-switch/src/index.ts b/packages/beta-switch/src/index.ts
index b0522789f..5602cf97f 100644
--- a/packages/beta-switch/src/index.ts
+++ b/packages/beta-switch/src/index.ts
@@ -7,48 +7,6 @@ type UrlStructure = {
   tld: string;
 };
 
-const legacyProd: UrlStructure = {
-  protocol: "https://",
-  hostname: "thunderstore.io",
-  port: "",
-  tld: "io",
-};
-
-const betaProd: UrlStructure = {
-  protocol: "https://",
-  hostname: "new.thunderstore.io",
-  port: "",
-  tld: "io",
-};
-
-const legacyQA: UrlStructure = {
-  protocol: "https://",
-  hostname: "thunderstore.dev",
-  port: "",
-  tld: "dev",
-};
-
-const betaQA: UrlStructure = {
-  protocol: "https://",
-  hostname: "new.thunderstore.dev",
-  port: "",
-  tld: "dev",
-};
-
-const legacyDev: UrlStructure = {
-  protocol: "http://",
-  hostname: "thunderstore.temp",
-  port: "",
-  tld: "temp",
-};
-
-const betaDev: UrlStructure = {
-  protocol: "http://",
-  hostname: "new.thunderstore.temp",
-  port: "",
-  tld: "temp",
-};
-
 async function checkBetaRedirect(
   legacy: UrlStructure,
   beta: UrlStructure,
@@ -178,28 +136,92 @@ async function insertSwitchButton(legacy: UrlStructure, beta: UrlStructure) {
   }
 }
 
-const legacy = window.location.hostname.endsWith(legacyProd.tld)
-  ? legacyProd
-  : window.location.hostname.endsWith(legacyQA.tld)
-    ? legacyQA
-    : legacyDev;
-const beta = window.location.hostname.endsWith(betaProd.tld)
-  ? betaProd
-  : window.location.hostname.endsWith(betaQA.tld)
-    ? betaQA
-    : betaDev;
-
-async function insertSwitchButtonListener() {
-  insertSwitchButton(legacy, beta);
-  document.removeEventListener("DOMContentLoaded", insertSwitchButtonListener);
+function hasBrowserGlobals(): boolean {
+  return typeof window !== "undefined" && typeof document !== "undefined";
 }
 
-// Run above code
-if (
-  document.readyState === "complete" ||
-  document.readyState === "interactive"
-) {
-  insertSwitchButton(legacy, beta);
-} else {
-  document.addEventListener("DOMContentLoaded", insertSwitchButtonListener);
+export function initBetaSwitch() {
+  if (!hasBrowserGlobals()) {
+    return;
+  }
+
+  const globalWindow = window as unknown as Record<string, unknown>;
+  const initFlag = "__thunderstore_beta_switch_initialized__";
+  if (globalWindow[initFlag]) {
+    return;
+  }
+  globalWindow[initFlag] = true;
+
+  const legacyProd: UrlStructure = {
+    protocol: "https://",
+    hostname: "thunderstore.io",
+    port: "",
+    tld: "io",
+  };
+
+  const betaProd: UrlStructure = {
+    protocol: "https://",
+    hostname: "new.thunderstore.io",
+    port: "",
+    tld: "io",
+  };
+
+  const legacyQA: UrlStructure = {
+    protocol: "https://",
+    hostname: "thunderstore.dev",
+    port: "",
+    tld: "dev",
+  };
+
+  const betaQA: UrlStructure = {
+    protocol: "https://",
+    hostname: "new.thunderstore.dev",
+    port: "",
+    tld: "dev",
+  };
+
+  const legacyDev: UrlStructure = {
+    protocol: "http://",
+    hostname: "thunderstore.localhost",
+    port: "",
+    tld: "localhost",
+  };
+
+  const betaDev: UrlStructure = {
+    protocol: "http://",
+    hostname: "new.thunderstore.localhost",
+    port: "",
+    tld: "localhost",
+  };
+
+  const legacy = window.location.hostname.endsWith(legacyProd.tld)
+    ? legacyProd
+    : window.location.hostname.endsWith(legacyQA.tld)
+      ? legacyQA
+      : legacyDev;
+  const beta = window.location.hostname.endsWith(betaProd.tld)
+    ? betaProd
+    : window.location.hostname.endsWith(betaQA.tld)
+      ? betaQA
+      : betaDev;
+
+  async function insertSwitchButtonListener() {
+    insertSwitchButton(legacy, beta);
+    document.removeEventListener(
+      "DOMContentLoaded",
+      insertSwitchButtonListener
+    );
+  }
+
+  if (
+    document.readyState === "complete" ||
+    document.readyState === "interactive"
+  ) {
+    insertSwitchButton(legacy, beta);
+  } else {
+    document.addEventListener("DOMContentLoaded", insertSwitchButtonListener);
+  }
 }
+
+// Backwards compatible: importing the module in the browser initializes it.
+initBetaSwitch();
diff --git a/packages/beta-switch/vitest.config.ts b/packages/beta-switch/vitest.config.ts
new file mode 100644
index 000000000..423140a57
--- /dev/null
+++ b/packages/beta-switch/vitest.config.ts
@@ -0,0 +1,15 @@
+import { defineProject } from "vitest/config";
+
+const packageRoot = new URL("./", import.meta.url).pathname;
+
+export default defineProject({
+  root: packageRoot,
+  test: {
+    include: ["src/**/__tests__/**/*.test.ts"],
+    exclude: ["dist/**/*"],
+    environment: "node",
+    browser: {
+      enabled: false,
+    },
+  },
+});