diff --git a/include/cserver/engine/not_implemented.hpp b/include/cserver/engine/not_implemented.hpp
new file mode 100644
index 0000000..d10200e
--- /dev/null
+++ b/include/cserver/engine/not_implemented.hpp
@@ -0,0 +1,10 @@
+#include <stdexcept>
+
+
+namespace cserver::engine {
+
+struct NotImplemented : std::runtime_error {
+  using std::runtime_error::runtime_error;
+};
+
+} // namespace cserver::engine