diff --git a/packages/core-shared/src/lib/env.test.ts b/packages/core-shared/src/lib/env.test.ts
new file mode 100644
index 0000000..a586a55
--- /dev/null
+++ b/packages/core-shared/src/lib/env.test.ts
@@ -0,0 +1,28 @@
+import { describe, expect, it, afterEach } from "vitest";
+import { requireEnv } from "./env";
+
+describe("requireEnv", () => {
+  const originalEnv = process.env.SOME_KEY;
+
+  afterEach(() => {
+    if (originalEnv === undefined) delete process.env.SOME_KEY;
+    else process.env.SOME_KEY = originalEnv;
+  });
+
+  it("returns the value when set", () => {
+    process.env.SOME_KEY = "value";
+    expect(requireEnv("SOME_KEY")).toBe("value");
+  });
+
+  it("throws when missing", () => {
+    delete process.env.SOME_KEY;
+    expect(() => requireEnv("SOME_KEY")).toThrow(
+      /Missing required env var: SOME_KEY/,
+    );
+  });
+
+  it("throws when empty string", () => {
+    process.env.SOME_KEY = "";
+    expect(() => requireEnv("SOME_KEY")).toThrow();
+  });
+});
diff --git a/packages/core-shared/src/lib/env.ts b/packages/core-shared/src/lib/env.ts
new file mode 100644
index 0000000..8721f93
--- /dev/null
+++ b/packages/core-shared/src/lib/env.ts
@@ -0,0 +1,7 @@
+export function requireEnv(name: string): string {
+  const value = process.env[name];
+  if (!value) {
+    throw new Error(`Missing required env var: ${name}`);
+  }
+  return value;
+}