diff --git a/llvm/tools/llvm-cas-fuzzer/CMakeLists.txt b/llvm/tools/llvm-cas-fuzzer/CMakeLists.txt
new file mode 100644
index 0000000000000..635cda4538aa0
--- /dev/null
+++ b/llvm/tools/llvm-cas-fuzzer/CMakeLists.txt
@@ -0,0 +1,9 @@
+set(LLVM_LINK_COMPONENTS
+    CAS
+    FuzzerCLI
+    FuzzMutate
+    Support
+)
+add_llvm_fuzzer(llvm-cas-fuzzer
+  llvm-cas-fuzzer.cpp
+  )
diff --git a/llvm/tools/llvm-cas-fuzzer/llvm-cas-fuzzer.cpp b/llvm/tools/llvm-cas-fuzzer/llvm-cas-fuzzer.cpp
new file mode 100644
index 0000000000000..3b4371252026e
--- /dev/null
+++ b/llvm/tools/llvm-cas-fuzzer/llvm-cas-fuzzer.cpp
@@ -0,0 +1,88 @@
+#include "llvm/ADT/ScopeExit.h"
+#include "llvm/CAS/ActionCache.h"
+#include "llvm/CAS/BuiltinUnifiedCASDatabases.h"
+#include "llvm/CAS/ObjectStore.h"
+#include "llvm/Support/ThreadPool.h"
+
+using namespace llvm;
+
+extern "C" int LLVMFuzzerInitialize(int *argc, char ***argv) { return 0; }
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
+  static ExitOnError ExitOnErr("llvm-cas-fuzzer: ");
+
+  if (Size == 0)
+    return 0;
+
+  SmallString<128> Path;
+  if (sys::fs::createUniqueDirectory("CAS", Path) != std::error_code())
+    return 1;
+
+  ExitOnErr.setBanner(("llvm-cas-fuzzer using '" + Path + "':").str());
+
+  size_t NumShards = std::max(uint8_t(1), std::min(Data[0], uint8_t(32)));
+  ++Data;
+  --Size;
+
+  StringRef GlobalData(reinterpret_cast<const char *>(Data), Size);
+
+  StdThreadPool ThreadPool(hardware_concurrency());
+
+  for (size_t I = 0; I != NumShards; ++I) {
+    ThreadPool.async([&, I] {
+      auto [CAS, ActionCache] =
+          ExitOnErr(cas::createOnDiskUnifiedCASDatabases(Path));
+
+      ExitOnErr(CAS->setSizeLimit(128));
+
+      StringRef LocalData =
+          GlobalData.drop_front(std::min(I, GlobalData.size()));
+
+      std::string KeySuffix = std::to_string(I);
+
+      std::string KeyIDStr;
+      {
+        cas::ObjectRef DataRef = ExitOnErr(CAS->storeFromString({}, LocalData));
+        cas::CASID DataID = CAS->getID(DataRef);
+
+        cas::ObjectRef KeyPrefixRef =
+            ExitOnErr(CAS->storeFromString({}, "key"));
+        cas::ObjectRef KeySuffixRef =
+            ExitOnErr(CAS->storeFromString({}, KeySuffix));
+        cas::ObjectRef KeyRef =
+            ExitOnErr(CAS->storeFromString({KeyPrefixRef, KeySuffixRef}, "_"));
+        cas::CASID KeyID = CAS->getID(KeyRef);
+        ExitOnErr(ActionCache->put(KeyID, DataID));
+        KeyIDStr = KeyID.toString();
+      }
+
+      {
+        cas::CASID KeyID = ExitOnErr(CAS->parseID(KeyIDStr));
+        auto MaybeKeyRef = CAS->getReference(KeyID);
+        assert(MaybeKeyRef);
+        cas::ObjectProxy KeyProxy = ExitOnErr(CAS->getProxy(*MaybeKeyRef));
+        assert(KeyProxy.getData() == "_");
+        assert(KeyProxy.getNumReferences() == 2);
+        cas::ObjectProxy KeyPrefixProxy =
+            ExitOnErr(CAS->getProxy(KeyProxy.getReference(0)));
+        assert(KeyPrefixProxy.getData() == "key");
+        cas::ObjectProxy KeySuffixProxy =
+            ExitOnErr(CAS->getProxy(KeyProxy.getReference(1)));
+        assert(KeySuffixProxy.getData() == KeySuffix);
+
+        auto MaybeDataID = ExitOnErr(ActionCache->get(KeyID));
+        assert(MaybeDataID);
+        cas::ObjectProxy DataProxy = ExitOnErr(CAS->getProxy(*MaybeDataID));
+        assert(DataProxy.getData() == LocalData);
+      }
+
+      ExitOnErr(CAS->pruneStorageData());
+    });
+  }
+
+  ThreadPool.wait();
+
+  sys::fs::remove_directories(Path);
+
+  return 0;
+}