diff --git a/source/types.d.ts b/source/types.d.ts
index 9d8f154..fb653d0 100644
--- a/source/types.d.ts
+++ b/source/types.d.ts
@@ -29,4 +29,8 @@ declare global {
 
     type MoveDirection = 'up' | 'down';
   }
+
+  const $browser: 'chromium' | 'firefox';
+  const $dev: boolean;
+  const $test: boolean;
 }