diff --git a/libraries/core/moon.yml b/libraries/core/moon.yml
index de3b64c0..55617fb2 100644
--- a/libraries/core/moon.yml
+++ b/libraries/core/moon.yml
@@ -5,4 +5,3 @@ tasks:
   build:
     outputs:
       - 'esm'
-      - 'lib'
diff --git a/libraries/core/package.json b/libraries/core/package.json
index c57a4465..e18235fd 100644
--- a/libraries/core/package.json
+++ b/libraries/core/package.json
@@ -16,8 +16,7 @@
   },
   "packemon": {
     "format": [
-      "esm",
-      "umd"
+      "esm"
     ],
     "platform": "browser"
   },
@@ -26,13 +25,11 @@
   },
   "files": [
     "esm/**/*",
-    "lib/**/*",
-    "src/**/*",
-    "umd/**/*"
+    "src/**/*"
   ],
   "main": "./esm/index.js",
   "module": "./esm/index.js",
-  "types": "./lib/index.d.ts",
+  "types": "./esm/index.d.ts",
   "exports": {
     "./package.json": "./package.json",
     ".": {
@@ -56,6 +53,5 @@
     "@types/node": "^22.7.5",
     "@types/sockjs-client": "^1.5.4",
     "@types/uuid": "^10.0.0"
-  },
-  "browser": "./umd/index.js"
+  }
 }
diff --git a/libraries/core/src/polyfills/index.js b/libraries/core/src/polyfills/index.cjs
similarity index 100%
rename from libraries/core/src/polyfills/index.js
rename to libraries/core/src/polyfills/index.cjs
diff --git a/libraries/core/tsconfig.umd.json b/libraries/core/tsconfig.umd.json
deleted file mode 100644
index b5102ebe..00000000
--- a/libraries/core/tsconfig.umd.json
+++ /dev/null
@@ -1,11 +0,0 @@
-{
-  "extends": "../../tsconfig.options.json",
-  "compilerOptions": {
-    "outDir": "lib",
-    "rootDir": "src"
-  },
-  "include": [
-    "src/**/*"
-  ],
-  "references": []
-}