diff --git a/include/xo/arena/AllocHeader.hpp b/include/xo/arena/AllocHeader.hpp
new file mode 100644
index 0000000..ec99f59
--- /dev/null
+++ b/include/xo/arena/AllocHeader.hpp
@@ -0,0 +1,28 @@
+/** @file AllocHeader.hpp
+ *
+ *  @author Roland Conybeare, Dec 2025
+ **/
+
+#pragma once
+
+#include <type_traits>
+#include <cstdint>
+#include <cstddef>
+
+namespace xo {
+    namespace mm {
+        struct AllocHeader {
+            using repr_type = std::uintptr_t;
+            using size_type = std::size_t;
+
+            explicit AllocHeader(repr_type x) : repr_{x} {}
+
+            repr_type repr_;
+        };
+
+        static_assert(sizeof(AllocHeader) == sizeof(AllocHeader::repr_type));
+        static_assert(std::is_standard_layout_v<AllocHeader>);
+    }
+}
+
+/* end AllocHeader.hpp */