diff --git a/pkg/compiler/lib/src/js/rewrite_async.dart b/pkg/compiler/lib/src/js/rewrite_async.dart
index 7cc6ec9bd8a..82d166222ff 100644
--- a/pkg/compiler/lib/src/js/rewrite_async.dart
+++ b/pkg/compiler/lib/src/js/rewrite_async.dart
@@ -9,7 +9,7 @@ library rewrite_async;
 import 'dart:collection';
 import 'dart:math' show max;
 
-import 'package:js_runtime/shared/async_await_error_codes.dart' as error_codes;
+import 'package:js_runtime/synced/async_await_error_codes.dart' as error_codes;
 
 import '../common.dart';
 import '../io/source_information.dart' show SourceInformation;
diff --git a/pkg/compiler/lib/src/js_backend/backend_usage.dart b/pkg/compiler/lib/src/js_backend/backend_usage.dart
index 7e08bd6f23f..37ef5340ad8 100644
--- a/pkg/compiler/lib/src/js_backend/backend_usage.dart
+++ b/pkg/compiler/lib/src/js_backend/backend_usage.dart
@@ -161,7 +161,8 @@ class BackendUsageBuilderImpl implements BackendUsageBuilder {
     if (_isValidEntity(element)) return true;
     SourceSpan span = _frontendStrategy.spanFromSpannable(element, element);
     if (library.canonicalUri.isScheme('dart') &&
-        span.uri.path.contains('_internal/js_runtime/lib/')) {
+        (span.uri.path.contains('_internal/js_runtime/lib') ||
+            span.uri.path.contains('_internal/js_shared/lib'))) {
       // TODO(johnniwinther): We should be more precise about these.
       return true;
     } else {
diff --git a/pkg/compiler/lib/src/js_backend/namer.dart b/pkg/compiler/lib/src/js_backend/namer.dart
index 3f90fc2147e..392e4e5c277 100644
--- a/pkg/compiler/lib/src/js_backend/namer.dart
+++ b/pkg/compiler/lib/src/js_backend/namer.dart
@@ -9,7 +9,7 @@ library js_backend.namer;
 import 'package:front_end/src/api_unstable/dart2js.dart'
     show $0, $9, $A, $Z, $_, $a, $g, $s, $z;
 
-import 'package:js_runtime/shared/embedded_names.dart' show JsGetName;
+import 'package:js_runtime/synced/embedded_names.dart' show JsGetName;
 
 import '../closure.dart';
 import '../common.dart';
diff --git a/pkg/compiler/lib/src/js_backend/runtime_types_new.dart b/pkg/compiler/lib/src/js_backend/runtime_types_new.dart
index 2f8816e30f5..a0f41615392 100644
--- a/pkg/compiler/lib/src/js_backend/runtime_types_new.dart
+++ b/pkg/compiler/lib/src/js_backend/runtime_types_new.dart
@@ -6,7 +6,7 @@
 
 library js_backend.runtime_types_new;
 
-import 'package:js_runtime/shared/recipe_syntax.dart';
+import 'package:js_shared/synced/recipe_syntax.dart';
 
 import '../common/elements.dart' show CommonElements, JCommonElements;
 import '../elements/entities.dart';
diff --git a/pkg/compiler/lib/src/js_emitter/class_stub_generator.dart b/pkg/compiler/lib/src/js_emitter/class_stub_generator.dart
index 78a6912539e..0e142536c99 100644
--- a/pkg/compiler/lib/src/js_emitter/class_stub_generator.dart
+++ b/pkg/compiler/lib/src/js_emitter/class_stub_generator.dart
@@ -6,7 +6,7 @@
 
 library dart2js.js_emitter.class_stub_generator;
 
-import 'package:js_runtime/shared/embedded_names.dart'
+import 'package:js_runtime/synced/embedded_names.dart'
     show TearOffParametersPropertyNames;
 
 import '../common/elements.dart' show CommonElements;
diff --git a/pkg/compiler/lib/src/js_emitter/interceptor_stub_generator.dart b/pkg/compiler/lib/src/js_emitter/interceptor_stub_generator.dart
index 7ba3a7f1827..525136589fd 100644
--- a/pkg/compiler/lib/src/js_emitter/interceptor_stub_generator.dart
+++ b/pkg/compiler/lib/src/js_emitter/interceptor_stub_generator.dart
@@ -6,7 +6,7 @@
 
 library dart2js.js_emitter.interceptor_stub_generator;
 
-import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
+import 'package:js_runtime/synced/embedded_names.dart' as embeddedNames;
 
 import '../common/elements.dart';
 import '../constants/values.dart';
diff --git a/pkg/compiler/lib/src/js_emitter/main_call_stub_generator.dart b/pkg/compiler/lib/src/js_emitter/main_call_stub_generator.dart
index 60984933fcf..c6af592d789 100644
--- a/pkg/compiler/lib/src/js_emitter/main_call_stub_generator.dart
+++ b/pkg/compiler/lib/src/js_emitter/main_call_stub_generator.dart
@@ -7,7 +7,7 @@
 library dart2js.js_emitter.main_call_stub_generator;
 
 import 'package:compiler/src/options.dart';
-import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
+import 'package:js_runtime/synced/embedded_names.dart' as embeddedNames;
 
 import '../common/elements.dart';
 import '../elements/entities.dart';
diff --git a/pkg/compiler/lib/src/js_emitter/native_generator.dart b/pkg/compiler/lib/src/js_emitter/native_generator.dart
index 71e641461c2..a47b6bed4c8 100644
--- a/pkg/compiler/lib/src/js_emitter/native_generator.dart
+++ b/pkg/compiler/lib/src/js_emitter/native_generator.dart
@@ -6,7 +6,7 @@
 
 library dart2js.js_emitter.native_generator;
 
-import 'package:js_runtime/shared/embedded_names.dart' as embeddedNames;
+import 'package:js_runtime/synced/embedded_names.dart' as embeddedNames;
 
 import '../js/js.dart' as jsAst;
 import '../js/js.dart' show js;
diff --git a/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart b/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
index f0ca98125af..9ff95c58c2f 100644
--- a/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/startup_emitter/model_emitter.dart
@@ -8,7 +8,7 @@ library dart2js.js_emitter.startup_emitter.model_emitter;
 
 import 'dart:convert' show JsonEncoder;
 
-import 'package:js_runtime/shared/embedded_names.dart'
+import 'package:js_runtime/synced/embedded_names.dart'
     show
         ARRAY_RTI_PROPERTY,
         DEFERRED_INITIALIZED,
diff --git a/pkg/compiler/lib/src/kernel/element_map_impl.dart b/pkg/compiler/lib/src/kernel/element_map_impl.dart
index 476b9065806..f28ab293499 100644
--- a/pkg/compiler/lib/src/kernel/element_map_impl.dart
+++ b/pkg/compiler/lib/src/kernel/element_map_impl.dart
@@ -6,7 +6,7 @@
 
 import 'package:front_end/src/api_prototype/constant_evaluator.dart' as ir;
 import 'package:front_end/src/api_unstable/dart2js.dart' as ir;
-import 'package:js_runtime/shared/embedded_names.dart';
+import 'package:js_runtime/synced/embedded_names.dart';
 import 'package:kernel/ast.dart' as ir;
 import 'package:kernel/class_hierarchy.dart' as ir;
 import 'package:kernel/core_types.dart' as ir;
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index 8721f915439..cc261971184 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -4,7 +4,7 @@
 
 // @dart = 2.10
 
-import 'package:js_runtime/shared/embedded_names.dart';
+import 'package:js_runtime/synced/embedded_names.dart';
 import 'package:kernel/ast.dart' as ir;
 
 import '../closure.dart';
diff --git a/pkg/compiler/pubspec.yaml b/pkg/compiler/pubspec.yaml
index 22f0ac47c34..f3dfd2624c2 100644
--- a/pkg/compiler/pubspec.yaml
+++ b/pkg/compiler/pubspec.yaml
@@ -17,6 +17,7 @@ dependencies:
   front_end: any
   js_ast: any
   js_runtime: any
+  js_shared: any
   kernel: any
 
 dev_dependencies:
diff --git a/pkg/js_runtime/README.md b/pkg/js_runtime/README.md
index 5f60952023f..02f263b9e07 100644
--- a/pkg/js_runtime/README.md
+++ b/pkg/js_runtime/README.md
@@ -3,7 +3,7 @@
 This package contains code that is shared between the dart2js compiler and the
 dart2js runtime libraries.
 
-*Important*: all code under the `lib/shared/` must be kept in sync with the
-runtime at all times (in `sdk/lib/_internal/js_runtime/lib/shared`). The
+*Important*: all code under the `lib/synced/` must be kept in sync with the
+runtime at all times (in `sdk/lib/_internal/js_runtime/lib/synced`). The
 `test/in_sync_test.dart` test verifies this.
 
diff --git a/pkg/js_runtime/lib/shared/async_await_error_codes.dart b/pkg/js_runtime/lib/synced/async_await_error_codes.dart
similarity index 100%
rename from pkg/js_runtime/lib/shared/async_await_error_codes.dart
rename to pkg/js_runtime/lib/synced/async_await_error_codes.dart
diff --git a/pkg/js_runtime/lib/shared/embedded_names.dart b/pkg/js_runtime/lib/synced/embedded_names.dart
similarity index 100%
rename from pkg/js_runtime/lib/shared/embedded_names.dart
rename to pkg/js_runtime/lib/synced/embedded_names.dart
diff --git a/pkg/js_runtime/test/in_sync_test.dart b/pkg/js_runtime/test/in_sync_test.dart
index 4dbef635035..5dab5865cad 100644
--- a/pkg/js_runtime/test/in_sync_test.dart
+++ b/pkg/js_runtime/test/in_sync_test.dart
@@ -11,9 +11,9 @@ import 'package:_fe_analyzer_shared/src/util/relativize.dart';
 import 'package:expect/expect.dart';
 
 void main(List<String> argv) {
-  var packageDir = Platform.script.resolve('../lib/shared/');
+  var packageDir = Platform.script.resolve('../lib/synced/');
   var sdkDir = Platform.script
-      .resolve('../../../sdk/lib/_internal/js_runtime/lib/shared/');
+      .resolve('../../../sdk/lib/_internal/js_runtime/lib/synced/');
   var rPackageDir =
       relativizeUri(Directory.current.uri, packageDir, Platform.isWindows);
   var rSdkDir =
diff --git a/pkg/js_shared/OWNERS b/pkg/js_shared/OWNERS
new file mode 100644
index 00000000000..f5bd90c5161
--- /dev/null
+++ b/pkg/js_shared/OWNERS
@@ -0,0 +1 @@
+file:/tools/OWNERS_WEB
diff --git a/pkg/js_shared/README.md b/pkg/js_shared/README.md
new file mode 100644
index 00000000000..cce9c2e74b1
--- /dev/null
+++ b/pkg/js_shared/README.md
@@ -0,0 +1,13 @@
+# Package `js_shared`:
+
+This code is a compile time dependency of dart2js and DDC. It is imported as
+a `package:` import by both compilers.
+
+There is an exact copy in the SDK of the libraries in the
+`pkg/js_shared/lib/synced` sub-directory.
+Those libraries are imported as `dart:` imports by the dart2js and DDC runtime
+libraries.
+
+*Important*: all code under `pkg/js_shared/lib/synced` must be kept in sync with
+the runtime (in `sdk/lib/_internal/js_shared/lib/synced`) at all times. The
+`test/in_sync_test.dart` test verifies this.
diff --git a/pkg/js_runtime/lib/shared/recipe_syntax.dart b/pkg/js_shared/lib/synced/recipe_syntax.dart
similarity index 98%
rename from pkg/js_runtime/lib/shared/recipe_syntax.dart
rename to pkg/js_shared/lib/synced/recipe_syntax.dart
index 73054919a2b..3ccec6070ca 100644
--- a/pkg/js_runtime/lib/shared/recipe_syntax.dart
+++ b/pkg/js_shared/lib/synced/recipe_syntax.dart
@@ -6,8 +6,8 @@
 
 /// Constants and predicates used for encoding and decoding type recipes.
 ///
-/// This library is shared between the compiler and the runtime system.
-library dart2js._recipe_syntax;
+/// This library is synchronized between the compiler and the runtime system.
+library js_shared._recipe_syntax;
 
 abstract class Recipe {
   Recipe._();
diff --git a/pkg/js_shared/pubspec.yaml b/pkg/js_shared/pubspec.yaml
new file mode 100644
index 00000000000..6424aac62ec
--- /dev/null
+++ b/pkg/js_shared/pubspec.yaml
@@ -0,0 +1,10 @@
+name: js_shared
+# This package is not intended for consumption on pub.dev. DO NOT publish.
+publish_to: none
+
+environment:
+  sdk: '>=2.12.0 <3.0.0'
+
+dev_dependencies:
+  expect: any
+  _fe_analyzer_shared: any
diff --git a/pkg/js_shared/test/in_sync_test.dart b/pkg/js_shared/test/in_sync_test.dart
new file mode 100644
index 00000000000..e10c4d6b665
--- /dev/null
+++ b/pkg/js_shared/test/in_sync_test.dart
@@ -0,0 +1,37 @@
+// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Test to verify that this package is in-sync with shared runtime libraries.
+import 'dart:io';
+
+import 'package:_fe_analyzer_shared/src/util/relativize.dart';
+import 'package:expect/expect.dart';
+
+void main(List<String> argv) {
+  var packageDir = Platform.script.resolve('../lib/synced/');
+  var sdkDir = Platform.script
+      .resolve('../../../sdk/lib/_internal/js_shared/lib/synced/');
+  var rPackageDir =
+      relativizeUri(Directory.current.uri, packageDir, Platform.isWindows);
+  var rSdkDir =
+      relativizeUri(Directory.current.uri, sdkDir, Platform.isWindows);
+
+  for (var file in Directory.fromUri(sdkDir).listSync()) {
+    if (file is File) {
+      var filename = file.uri.pathSegments.last;
+      var packageFile = File.fromUri(packageDir.resolve(filename));
+      Expect.isTrue(
+          packageFile.existsSync(),
+          "$filename not in sync. Please update it by running:\n"
+          "  cp $rSdkDir$filename $rPackageDir$filename");
+      var original = file.readAsBytesSync();
+      var copy = packageFile.readAsBytesSync();
+      Expect.listEquals(
+          original,
+          copy,
+          "$filename not in sync. Please update it by running:\n"
+          "  cp $rSdkDir$filename $rPackageDir$filename");
+    }
+  }
+}
diff --git a/pkg/pkg.status b/pkg/pkg.status
index 2aef55f42ce..b7d194973c4 100644
--- a/pkg/pkg.status
+++ b/pkg/pkg.status
@@ -140,6 +140,7 @@ dev_compiler/test/options/*: SkipByDesign
 front_end/test/hot_reload_e2e_test: Skip
 frontend_server/test/*: SkipByDesign # Only meant to run on vm
 js_runtime/test/*: SkipByDesign # Only meant to run on vm
+js_shared/test/*: SkipByDesign # Only meant to run on vm
 vm/test/*: SkipByDesign # Only meant to run on vm
 vm_service/test/*: SkipByDesign # Uses dart:io
 vm_snapshot_analysis/test/*: SkipByDesign # Only meant to run on vm
diff --git a/sdk/lib/_internal/js_runtime/lib/shared/async_await_error_codes.dart b/sdk/lib/_internal/js_runtime/lib/synced/async_await_error_codes.dart
similarity index 100%
rename from sdk/lib/_internal/js_runtime/lib/shared/async_await_error_codes.dart
rename to sdk/lib/_internal/js_runtime/lib/synced/async_await_error_codes.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/shared/embedded_names.dart b/sdk/lib/_internal/js_runtime/lib/synced/embedded_names.dart
similarity index 100%
rename from sdk/lib/_internal/js_runtime/lib/shared/embedded_names.dart
rename to sdk/lib/_internal/js_runtime/lib/synced/embedded_names.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/rti.dart b/sdk/lib/_internal/js_shared/lib/rti.dart
similarity index 100%
rename from sdk/lib/_internal/js_runtime/lib/rti.dart
rename to sdk/lib/_internal/js_shared/lib/rti.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/shared/recipe_syntax.dart b/sdk/lib/_internal/js_shared/lib/synced/recipe_syntax.dart
similarity index 98%
rename from sdk/lib/_internal/js_runtime/lib/shared/recipe_syntax.dart
rename to sdk/lib/_internal/js_shared/lib/synced/recipe_syntax.dart
index 73054919a2b..3ccec6070ca 100644
--- a/sdk/lib/_internal/js_runtime/lib/shared/recipe_syntax.dart
+++ b/sdk/lib/_internal/js_shared/lib/synced/recipe_syntax.dart
@@ -6,8 +6,8 @@
 
 /// Constants and predicates used for encoding and decoding type recipes.
 ///
-/// This library is shared between the compiler and the runtime system.
-library dart2js._recipe_syntax;
+/// This library is synchronized between the compiler and the runtime system.
+library js_shared._recipe_syntax;
 
 abstract class Recipe {
   Recipe._();
diff --git a/sdk/lib/_internal/sdk_library_metadata/lib/libraries.dart b/sdk/lib/_internal/sdk_library_metadata/lib/libraries.dart
index 49845a23e81..5a357e5454b 100644
--- a/sdk/lib/_internal/sdk_library_metadata/lib/libraries.dart
+++ b/sdk/lib/_internal/sdk_library_metadata/lib/libraries.dart
@@ -147,7 +147,7 @@ const Map<String, LibraryInfo> libraries = const {
       categories: "", documented: false, platforms: DART2JS_PLATFORM),
   "_late_helper": const LibraryInfo("_internal/js_runtime/lib/late_helper.dart",
       categories: "", documented: false, platforms: DART2JS_PLATFORM),
-  "_rti": const LibraryInfo("_internal/js_runtime/lib/rti.dart",
+  "_rti": const LibraryInfo("_internal/js_shared/lib/rti.dart",
       categories: "", documented: false, platforms: DART2JS_PLATFORM),
   "_dart2js_runtime_metrics": const LibraryInfo(
       "_internal/js_runtime/lib/dart2js_runtime_metrics.dart",
@@ -172,17 +172,17 @@ const Map<String, LibraryInfo> libraries = const {
       documented: false,
       platforms: DART2JS_PLATFORM),
   "_js_embedded_names": const LibraryInfo(
-      "_internal/js_runtime/lib/shared/embedded_names.dart",
+      "_internal/js_runtime/lib/synced/embedded_names.dart",
       categories: "",
       documented: false,
       platforms: DART2JS_PLATFORM),
   "_async_await_error_codes": const LibraryInfo(
-      "_internal/js_runtime/lib/shared/async_await_error_codes.dart",
+      "_internal/js_runtime/lib/synced/async_await_error_codes.dart",
       categories: "",
       documented: false,
       platforms: DART2JS_PLATFORM),
   "_recipe_syntax": const LibraryInfo(
-      "_internal/js_runtime/lib/shared/recipe_syntax.dart",
+      "_internal/js_shared/lib/synced/recipe_syntax.dart",
       categories: "",
       documented: false,
       platforms: DART2JS_PLATFORM),
diff --git a/sdk/lib/libraries.json b/sdk/lib/libraries.json
index b72ab821a32..6f33d88fad0 100644
--- a/sdk/lib/libraries.json
+++ b/sdk/lib/libraries.json
@@ -369,7 +369,7 @@
         "uri": "_internal/js_runtime/lib/late_helper.dart"
       },
       "_rti": {
-        "uri": "_internal/js_runtime/lib/rti.dart"
+        "uri": "_internal/js_shared/lib/rti.dart"
       },
       "_interceptors": {
         "uri": "_internal/js_runtime/lib/interceptors.dart"
@@ -384,13 +384,13 @@
         "uri": "_internal/js_runtime/lib/js_primitives.dart"
       },
       "_js_embedded_names": {
-        "uri": "_internal/js_runtime/lib/shared/embedded_names.dart"
+        "uri": "_internal/js_runtime/lib/synced/embedded_names.dart"
       },
       "_async_await_error_codes": {
-        "uri": "_internal/js_runtime/lib/shared/async_await_error_codes.dart"
+        "uri": "_internal/js_runtime/lib/synced/async_await_error_codes.dart"
       },
       "_recipe_syntax": {
-        "uri": "_internal/js_runtime/lib/shared/recipe_syntax.dart"
+        "uri": "_internal/js_shared/lib/synced/recipe_syntax.dart"
       }
     }
   },
diff --git a/sdk/lib/libraries.yaml b/sdk/lib/libraries.yaml
index 92231cb4e61..ed11fa53e7e 100644
--- a/sdk/lib/libraries.yaml
+++ b/sdk/lib/libraries.yaml
@@ -337,7 +337,7 @@ _dart2js_common:
       uri: "_internal/js_runtime/lib/late_helper.dart"
 
     _rti:
-      uri: "_internal/js_runtime/lib/rti.dart"
+      uri: "_internal/js_shared/lib/rti.dart"
 
     _interceptors:
       uri: "_internal/js_runtime/lib/interceptors.dart"
@@ -352,13 +352,13 @@ _dart2js_common:
       uri: "_internal/js_runtime/lib/js_primitives.dart"
 
     _js_embedded_names:
-      uri: "_internal/js_runtime/lib/shared/embedded_names.dart"
+      uri: "_internal/js_runtime/lib/synced/embedded_names.dart"
 
     _async_await_error_codes:
-      uri: "_internal/js_runtime/lib/shared/async_await_error_codes.dart"
+      uri: "_internal/js_runtime/lib/synced/async_await_error_codes.dart"
 
     _recipe_syntax:
-      uri: "_internal/js_runtime/lib/shared/recipe_syntax.dart"
+      uri: "_internal/js_shared/lib/synced/recipe_syntax.dart"
 
 dartdevc:
     libraries: