diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index e3bac97..e0c88cc 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -99,5 +99,56 @@ set_property(
     PROPERTY INTERPROCEDURAL_OPTIMIZATION ${UMB_IPO_SUPPORTED}
 )
 
+add_executable(
+    umb_echo_server
+    umb_echo_server.cpp
+)
+target_link_libraries(
+    umb_echo_server
+    PRIVATE
+    Boost::boost
+    umb
+    test_msg_library
+)
+
+set_property(
+    TARGET umb_echo_server
+    PROPERTY INTERPROCEDURAL_OPTIMIZATION ${UMB_IPO_SUPPORTED}
+)
+
+if (MSCV)
+    set(
+        UMB_ECHO_SERVER_COMPILE_OPTIONS
+        /await
+    )
+else ()
+    set(
+        UMB_ECHO_SERVER_COMPILE_OPTIONS
+        -fcoroutines
+    )
+endif ()
+
+target_compile_options(
+    umb_echo_server
+    PRIVATE
+    ${UMB_ECHO_SERVER_COMPILE_OPTIONS}
+)
+
+target_compile_features(
+    umb_echo_server
+    PRIVATE
+    cxx_std_23
+)
+
+# Avoid executable not being found in later targets due to
+# MSVC added /Debug /Release paths.
+if (MSVC)
+    set_target_properties(umb_echo_server
+        PROPERTIES
+        RUNTIME_OUTPUT_DIRECTORY_DEBUG ${CMAKE_BINARY_DIR}
+        RUNTIME_OUTPUT_DIRECTORY_RELEASE ${CMAKE_BINARY_DIR}
+    )
+endif ()
+
 # TODO: clean up all the unneeded dependency links. The graph is a mess.
 # TODO: make reusable CMake functions to be used in other projects.
diff --git a/tests/umb_echo_server.cpp b/tests/umb_echo_server.cpp
new file mode 100644
index 0000000..767aa8d
--- /dev/null
+++ b/tests/umb_echo_server.cpp
@@ -0,0 +1,120 @@
+/*
+ * Copyright (C) 2023  Tuomo Kriikkula
+ * This program is free software: you can redistribute it and/or modify
+ *     it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ *     but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ *     along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * ****************************************************************************
+ *
+ * Copyright (c) 2003-2023 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+ *
+ * Distributed under the Boost Software License, Version 1.0. (See accompanying
+ * file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ *
+ */
+
+#include <iostream>
+#include <format>
+
+#include <boost/asio/co_spawn.hpp>
+#include <boost/asio/detached.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/ip/tcp.hpp>
+#include <boost/asio/signal_set.hpp>
+#include <boost/asio/write.hpp>
+
+#include "umb/umb.hpp"
+#include "TestMessages.umb.hpp"
+
+using boost::asio::ip::tcp;
+using boost::asio::awaitable;
+using boost::asio::co_spawn;
+using boost::asio::detached;
+using boost::asio::use_awaitable;
+namespace this_coro = boost::asio::this_coro;
+
+#if defined(BOOST_ASIO_ENABLE_HANDLER_TRACKING)
+# define use_awaitable \
+  boost::asio::use_awaitable_t(__FILE__, __LINE__, __PRETTY_FUNCTION__)
+#endif
+
+awaitable<void> echo(tcp::socket socket)
+{
+    try
+    {
+        std::array<umb::byte, 2048> data{};
+        std::array<umb::byte, 2048> msg_buf{};
+
+        for (;;)
+        {
+            std::size_t n = co_await socket.async_read_some(boost::asio::buffer(data),
+                                                            use_awaitable);
+
+            // Parse UMB message.
+            // Serialize it to bytes, send it back.
+
+            const auto size = static_cast<size_t>(data[0]);
+            std::cout << std::format("size: {}\n", size);
+
+            if (n < size)
+            {
+                std::cout << std::format("got {} bytes, size indicates {}, waiting for more...\n",
+                                         n, size);
+                throw std::runtime_error("TODO: handle this");
+            }
+
+            const auto part = data[1];
+            std::cout << std::format("part: {}\n", part);
+
+            const auto type = static_cast<testmessages::umb::MessageType>(
+                data[2] | (data[3] << 8));
+            std::cout << std::format("type: {}\n", testmessages::umb::meta::to_string(type));
+
+            co_await async_write(socket, boost::asio::buffer(data, n), use_awaitable);
+        }
+    }
+    catch (const std::exception& e)
+    {
+        std::cout << std::format("echo Exception: {}\n", e.what());
+    }
+}
+
+awaitable<void> listener()
+{
+    auto executor = co_await this_coro::executor;
+    tcp::acceptor acceptor(executor, {tcp::v4(), 55555});
+    for (;;)
+    {
+        tcp::socket socket = co_await acceptor.async_accept(use_awaitable);
+        co_spawn(executor, echo(std::move(socket)), detached);
+    }
+}
+
+int main()
+{
+    try
+    {
+        boost::asio::io_context io_context(1);
+
+        boost::asio::signal_set signals(io_context, SIGINT, SIGTERM);
+        signals.async_wait([&](auto, auto)
+                           { io_context.stop(); });
+
+        co_spawn(io_context, listener(), detached);
+
+        io_context.run();
+    }
+    catch (const std::exception& e)
+    {
+        std::cout << std::format("Exception: {}\n", e.what());
+    }
+}