diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index e527a330601..e1b3296c4e0 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -12,6 +12,7 @@ files: |
         media/base/starboard/|
         media/starboard/|
         starboard/|
+        third_party/blink/renderer/modules/cobalt/|
         components/viz/service/display/starboard/|
         ui/ozone/platform/starboard/|
         .pre-commit-config.yaml|
diff --git a/third_party/blink/renderer/bindings/generated_in_modules.gni b/third_party/blink/renderer/bindings/generated_in_modules.gni
index 7394d035208..2104bfb492e 100644
--- a/third_party/blink/renderer/bindings/generated_in_modules.gni
+++ b/third_party/blink/renderer/bindings/generated_in_modules.gni
@@ -2797,6 +2797,8 @@ if (is_cobalt) {
     "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_crash_annotator.h",
     "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_h_5_vcc.cc",
     "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_h_5_vcc.h",
+    "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_h_5_vcc_system.cc",
+    "$root_gen_dir/third_party/blink/renderer/bindings/modules/v8/v8_h_5_vcc_system.h",
   ]
 }
 
diff --git a/third_party/blink/renderer/bindings/idl_in_modules.gni b/third_party/blink/renderer/bindings/idl_in_modules.gni
index a9653c43645..32d5c937c96 100644
--- a/third_party/blink/renderer/bindings/idl_in_modules.gni
+++ b/third_party/blink/renderer/bindings/idl_in_modules.gni
@@ -1212,6 +1212,7 @@ if (is_cobalt) {
             "//third_party/blink/renderer/modules/cobalt/crash_annotator/crash_annotator.idl",
             "//third_party/blink/renderer/modules/cobalt/h_5_vcc.idl",
             "//third_party/blink/renderer/modules/cobalt/window_h_5_vcc.idl",
+            "//third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.idl",
           ],
           "abspath")
 }
diff --git a/third_party/blink/renderer/modules/BUILD.gn b/third_party/blink/renderer/modules/BUILD.gn
index b1989956316..d8bd3ee36bb 100644
--- a/third_party/blink/renderer/modules/BUILD.gn
+++ b/third_party/blink/renderer/modules/BUILD.gn
@@ -171,6 +171,7 @@ component("modules") {
     sub_modules += [
       "//third_party/blink/renderer/modules/cobalt:h_5_vcc",
       "//third_party/blink/renderer/modules/cobalt/crash_annotator",
+      "//third_party/blink/renderer/modules/cobalt/h5vcc_system",
     ]
   }
 
diff --git a/third_party/blink/renderer/modules/cobalt/BUILD.gn b/third_party/blink/renderer/modules/cobalt/BUILD.gn
index 7441313f2f2..2972145f424 100644
--- a/third_party/blink/renderer/modules/cobalt/BUILD.gn
+++ b/third_party/blink/renderer/modules/cobalt/BUILD.gn
@@ -19,5 +19,8 @@ blink_modules_sources("h_5_vcc") {
     "h_5_vcc.cc",
     "h_5_vcc.h",
   ]
-  deps = ["//third_party/blink/renderer/modules/cobalt/crash_annotator"]
+  deps = [
+    "//third_party/blink/renderer/modules/cobalt/crash_annotator",
+    "//third_party/blink/renderer/modules/cobalt/h5vcc_system",
+  ]
 }
diff --git a/third_party/blink/renderer/modules/cobalt/crash_annotator/crash_annotator.cc b/third_party/blink/renderer/modules/cobalt/crash_annotator/crash_annotator.cc
index 850e812c766..63adc6466dd 100644
--- a/third_party/blink/renderer/modules/cobalt/crash_annotator/crash_annotator.cc
+++ b/third_party/blink/renderer/modules/cobalt/crash_annotator/crash_annotator.cc
@@ -42,11 +42,9 @@ ScriptPromise CrashAnnotator::setString(ScriptState* script_state,
   EnsureReceiverIsBound();
 
   remote_crash_annotator_->SetString(
-      key,
-      value,
-      WTF::BindOnce(
-          &CrashAnnotator::OnSetString,
-          WrapPersistent(this), WrapPersistent(resolver)));
+      key, value,
+      WTF::BindOnce(&CrashAnnotator::OnSetString, WrapPersistent(this),
+                    WrapPersistent(resolver)));
 
   return resolver->Promise();
 }
diff --git a/third_party/blink/renderer/modules/cobalt/h5vcc_system/BUILD.gn b/third_party/blink/renderer/modules/cobalt/h5vcc_system/BUILD.gn
new file mode 100644
index 00000000000..53defb79277
--- /dev/null
+++ b/third_party/blink/renderer/modules/cobalt/h5vcc_system/BUILD.gn
@@ -0,0 +1,22 @@
+# Copyright 2025 The Cobalt Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import("//third_party/blink/renderer/modules/modules.gni")
+
+blink_modules_sources("h5vcc_system") {
+  sources = [
+    "h_5_vcc_system.cc",
+    "h_5_vcc_system.h",
+  ]
+}
diff --git a/third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.cc b/third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.cc
new file mode 100644
index 00000000000..a114ef0f1a6
--- /dev/null
+++ b/third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.cc
@@ -0,0 +1,36 @@
+// Copyright 2025 The Cobalt Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.h"
+
+#include "third_party/blink/renderer/core/frame/local_dom_window.h"
+
+namespace blink {
+
+H5vccSystem::H5vccSystem(LocalDOMWindow& window) {}
+
+const String H5vccSystem::advertisingId() const {
+  NOTIMPLEMENTED();
+
+  // TODO(b/377049113) add a mojom service and populate the value for
+  // advertising_id_.
+  //   return advertising_id_;
+  return String("fake advertisingId");
+}
+
+void H5vccSystem::Trace(Visitor* visitor) const {
+  ScriptWrappable::Trace(visitor);
+}
+
+}  // namespace blink
diff --git a/third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.h b/third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.h
new file mode 100644
index 00000000000..0284c30e847
--- /dev/null
+++ b/third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.h
@@ -0,0 +1,41 @@
+// Copyright 2025 The Cobalt Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef THIRD_PARTY_BLINK_RENDERER_MODULES_H5VCC_SYSTEM_H_5_VCC_SYSTEM_H_
+#define THIRD_PARTY_BLINK_RENDERER_MODULES_H5VCC_SYSTEM_H_5_VCC_SYSTEM_H_
+
+#include "third_party/blink/renderer/modules/modules_export.h"
+#include "third_party/blink/renderer/platform/bindings/script_wrappable.h"
+#include "third_party/blink/renderer/platform/wtf/text/wtf_string.h"
+
+namespace blink {
+
+class LocalDOMWindow;
+class ScriptState;
+
+class MODULES_EXPORT H5vccSystem final : public ScriptWrappable {
+  DEFINE_WRAPPERTYPEINFO();
+
+ public:
+  explicit H5vccSystem(LocalDOMWindow&);
+
+  // Web-exposed interface:
+  const String advertisingId() const;
+
+  void Trace(Visitor*) const override;
+};
+
+}  // namespace blink
+
+#endif  // THIRD_PARTY_BLINK_RENDERER_MODULES_H5VCC_SYSTEM_H_5_VCC_SYSTEM_H_
diff --git a/third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.idl b/third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.idl
new file mode 100644
index 00000000000..696095c75c5
--- /dev/null
+++ b/third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.idl
@@ -0,0 +1,23 @@
+// Copyright 2025 The Cobalt Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This interface mirrors the H5vccSystem Web IDL defined in Cobalt LTS 25:
+// https://github.com/youtube/cobalt/blob/25.lts.stable/cobalt/h5vcc/h5vcc_system.idl
+[
+    Exposed=Window,
+    SecureContext
+]
+interface H5vccSystem {
+    readonly attribute DOMString advertisingId;
+};
diff --git a/third_party/blink/renderer/modules/cobalt/h_5_vcc.cc b/third_party/blink/renderer/modules/cobalt/h_5_vcc.cc
index bd21a25dfcd..82c5720867b 100644
--- a/third_party/blink/renderer/modules/cobalt/h_5_vcc.cc
+++ b/third_party/blink/renderer/modules/cobalt/h_5_vcc.cc
@@ -16,13 +16,14 @@
 
 #include "third_party/blink/renderer/core/frame/local_dom_window.h"
 #include "third_party/blink/renderer/modules/cobalt/crash_annotator/crash_annotator.h"
+#include "third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.h"
 
 namespace blink {
 
 // static
 const char H5vcc::kSupplementName[] = "H5vcc";
 
-//static
+// static
 H5vcc* H5vcc::h5vcc(LocalDOMWindow& window) {
   H5vcc* h5vcc = Supplement<LocalDOMWindow>::From<H5vcc>(window);
   if (!h5vcc && window.GetExecutionContext()) {
@@ -34,10 +35,12 @@ H5vcc* H5vcc::h5vcc(LocalDOMWindow& window) {
 
 H5vcc::H5vcc(LocalDOMWindow& window)
     : Supplement<LocalDOMWindow>(window),
-      crash_annotator_(MakeGarbageCollected<CrashAnnotator>(window)) {}
+      crash_annotator_(MakeGarbageCollected<CrashAnnotator>(window)),
+      system_(MakeGarbageCollected<H5vccSystem>(window)) {}
 
 void H5vcc::Trace(Visitor* visitor) const {
   visitor->Trace(crash_annotator_);
+  visitor->Trace(system_);
   Supplement<LocalDOMWindow>::Trace(visitor);
   ScriptWrappable::Trace(visitor);
 }
diff --git a/third_party/blink/renderer/modules/cobalt/h_5_vcc.h b/third_party/blink/renderer/modules/cobalt/h_5_vcc.h
index 6bebc73af1e..0974da14adb 100644
--- a/third_party/blink/renderer/modules/cobalt/h_5_vcc.h
+++ b/third_party/blink/renderer/modules/cobalt/h_5_vcc.h
@@ -27,10 +27,10 @@ namespace blink {
 class ScriptState;
 class CrashAnnotator;
 class LocalDOMWindow;
+class H5vccSystem;
 
-class MODULES_EXPORT H5vcc final
-    : public ScriptWrappable,
-      public Supplement<LocalDOMWindow> {
+class MODULES_EXPORT H5vcc final : public ScriptWrappable,
+                                   public Supplement<LocalDOMWindow> {
   DEFINE_WRAPPERTYPEINFO();
 
  public:
@@ -43,12 +43,15 @@ class MODULES_EXPORT H5vcc final
 
   CrashAnnotator* crashAnnotator() { return crash_annotator_; }
 
+  H5vccSystem* system() { return system_; }
+
   void Trace(Visitor*) const override;
 
  private:
   Member<CrashAnnotator> crash_annotator_;
+  Member<H5vccSystem> system_;
 };
 
-}
+}  // namespace blink
 
 #endif  // THIRD_PARTY_BLINK_RENDERER_MODULES_COBALT_H_5_VCC_H_
diff --git a/third_party/blink/renderer/modules/cobalt/h_5_vcc.idl b/third_party/blink/renderer/modules/cobalt/h_5_vcc.idl
index fa8677effd1..731f76a8c71 100644
--- a/third_party/blink/renderer/modules/cobalt/h_5_vcc.idl
+++ b/third_party/blink/renderer/modules/cobalt/h_5_vcc.idl
@@ -12,10 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// This interface mirrors the H5vcc Web IDL defined in Cobalt LTS 25:
+// https://github.com/youtube/cobalt/blob/25.lts.stable/cobalt/h5vcc/h5vcc.idl
 [
     Exposed=Window,
     SecureContext
 ]
 interface H5vcc {
     readonly attribute CrashAnnotator crashAnnotator;
+    readonly attribute H5vccSystem system;
 };
diff --git a/third_party/blink/web_tests/external/wpt/cobalt/h5vcc-system/h5vcc-system.https.sub.html b/third_party/blink/web_tests/external/wpt/cobalt/h5vcc-system/h5vcc-system.https.sub.html
new file mode 100644
index 00000000000..1ff84f72cbd
--- /dev/null
+++ b/third_party/blink/web_tests/external/wpt/cobalt/h5vcc-system/h5vcc-system.https.sub.html
@@ -0,0 +1,15 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test H5vccSystem web API.</title>
+  <script src='/resources/testharness.js'></script>
+  <script src='/resources/testharnessreport.js'></script>
+</head>
+<body>
+  <script>
+    test(() => {
+        assert_equals(window.h5vcc.system.advertisingId, "fake advertisingId");
+    }, "H5vccSystem has the right property value");
+  </script>
+</body>
+</html>
\ No newline at end of file