diff --git a/include/rest_rpc/codec.h b/include/rest_rpc/codec.h
index 4905353..d28c9b1 100644
--- a/include/rest_rpc/codec.h
+++ b/include/rest_rpc/codec.h
@@ -5,18 +5,44 @@
 #include <charconv>
 #include <msgpack.hpp>
 
-namespace rest_rpc {
+namespace user_codec {
+struct rest_adl_tag {};
+} // namespace user_codec
 
-struct msgpack_codec {
+namespace rest_rpc {
+namespace detail {
+template <typename T, typename... Args>
+struct has_user_pack : std::false_type {};
+
+template <typename... Args>
+struct has_user_pack<
+    std::void_t<
+        // AdlTag{} trigger ADL lookup user_codec namespace
+        decltype(serialize(std::declval<user_codec::rest_adl_tag>(),
+                           std::declval<Args>()...))>,
+    Args...> : std::true_type {};
+
+template <typename... Args>
+inline constexpr bool has_user_pack_v = has_user_pack<void, Args...>::value;
+
+} // namespace detail
+
+struct rpc_codec {
   template <typename... Args> inline static auto pack_args(Args &&...args) {
     if constexpr (sizeof...(Args) == 0) {
       return std::string_view{};
     } else if constexpr (sizeof...(Args) == 1 && util::is_basic_v<Args...>) {
       return pack_one(std::forward<Args>(args)...);
     } else {
-      msgpack::sbuffer buffer(2 * 1024);
-      msgpack::pack(buffer, std::forward_as_tuple(std::forward<Args>(args)...));
-      return std::string(buffer.data(), buffer.size());
+      if constexpr (detail::has_user_pack_v<Args...>) {
+        return serialize(user_codec::rest_adl_tag{},
+                         std::forward<Args>(args)...);
+      } else {
+        msgpack::sbuffer buffer(2 * 1024);
+        msgpack::pack(buffer,
+                      std::forward_as_tuple(std::forward<Args>(args)...));
+        return std::string(buffer.data(), buffer.size());
+      }
     }
   }
 
@@ -33,12 +59,16 @@ struct msgpack_codec {
     } else if constexpr (std::is_same_v<std::string_view, T>) {
       return data;
     } else {
-      try {
-        static msgpack::unpacked msg;
-        msgpack::unpack(msg, data.data(), data.size());
-        return msg.get().as<T>();
-      } catch (...) {
-        throw std::invalid_argument("unpack failed: Args not match!");
+      if constexpr (detail::has_user_pack_v<T>) {
+        return deserialize<T>(user_codec::rest_adl_tag{}, data);
+      } else {
+        try {
+          static msgpack::unpacked msg;
+          msgpack::unpack(msg, data.data(), data.size());
+          return msg.get().as<T>();
+        } catch (...) {
+          throw std::invalid_argument("unpack failed: Args not match!");
+        }
       }
     }
   }
diff --git a/include/rest_rpc/rpc_client.hpp b/include/rest_rpc/rpc_client.hpp
index 739981b..2808de7 100644
--- a/include/rest_rpc/rpc_client.hpp
+++ b/include/rest_rpc/rpc_client.hpp
@@ -164,7 +164,7 @@ private:
   template <typename R, typename... Args>
   asio::awaitable<call_result<R>> call_impl(rest_rpc_header &header,
                                             Args &&...args) {
-    auto buf = msgpack_codec::pack_args(std::forward<Args>(args)...);
+    auto buf = rpc_codec::pack_args(std::forward<Args>(args)...);
     header.body_len = buf.size();
     if (cross_ending_) {
       prepare_for_send(header);
@@ -227,10 +227,10 @@ private:
     result.ec = (rpc_errc)socket_->body_[0];
     if constexpr (!std::is_void_v<R>) {
       if constexpr (util::is_basic_v<R>) {
-        result.value = msgpack_codec::unpack<R>(std::string_view(
+        result.value = rpc_codec::unpack<R>(std::string_view(
             socket_->body_.data() + 1, resp_header.body_len - 1));
       } else {
-        auto tp = msgpack_codec::unpack<std::tuple<R>>(std::string_view(
+        auto tp = rpc_codec::unpack<std::tuple<R>>(std::string_view(
             socket_->body_.data() + 1, resp_header.body_len - 1));
         result.value = std::move(std::get<0>(tp));
       }
diff --git a/include/rest_rpc/rpc_connection.hpp b/include/rest_rpc/rpc_connection.hpp
index 07bc3d3..633254a 100644
--- a/include/rest_rpc/rpc_connection.hpp
+++ b/include/rest_rpc/rpc_connection.hpp
@@ -238,7 +238,7 @@ asio::awaitable<std::error_code> rpc_context::response(Args &&...args) {
     co_return make_error_code(rpc_errc::rpc_context_init_failed);
   }
 
-  rpc_result result(msgpack_codec::pack_args(std::forward<Args>(args)...));
+  rpc_result result(rpc_codec::pack_args(std::forward<Args>(args)...));
   has_response_ = true;
   co_return co_await conn_->response(result);
 }
diff --git a/include/rest_rpc/rpc_router.hpp b/include/rest_rpc/rpc_router.hpp
index 8b8628b..1e25a66 100644
--- a/include/rest_rpc/rpc_router.hpp
+++ b/include/rest_rpc/rpc_router.hpp
@@ -148,15 +148,15 @@ private:
     } else {
       if constexpr (std::is_void_v<Self>) {
         if constexpr (is_awaitable_v<R>) {
-          ret = msgpack_codec::pack_args(co_await f());
+          ret = rpc_codec::pack_args(co_await f());
         } else {
-          ret = msgpack_codec::pack_args(f());
+          ret = rpc_codec::pack_args(f());
         }
       } else {
         if constexpr (is_awaitable_v<R>) {
-          ret = msgpack_codec::pack_args(co_await (*self.*f)());
+          ret = rpc_codec::pack_args(co_await (*self.*f)());
         } else {
-          ret = msgpack_codec::pack_args((*self.*f)());
+          ret = rpc_codec::pack_args((*self.*f)());
         }
       }
     }
@@ -169,32 +169,30 @@ private:
     if constexpr (is_void_v<R>) {
       if constexpr (std::is_void_v<Self>) {
         if constexpr (is_awaitable_v<R>) {
-          co_await f(msgpack_codec::unpack<Arg>(str));
+          co_await f(rpc_codec::unpack<Arg>(str));
         } else {
-          f(msgpack_codec::unpack<Arg>(str));
+          f(rpc_codec::unpack<Arg>(str));
         }
       } else {
         if constexpr (is_awaitable_v<R>) {
-          co_await (*self.*f)(msgpack_codec::unpack<Arg>(str));
+          co_await (*self.*f)(rpc_codec::unpack<Arg>(str));
         } else {
-          (*self.*f)(msgpack_codec::unpack<Arg>(str));
+          (*self.*f)(rpc_codec::unpack<Arg>(str));
         }
       }
     } else {
       if constexpr (std::is_void_v<Self>) {
         if constexpr (is_awaitable_v<R>) {
-          ret = msgpack_codec::pack_args(
-              co_await f(msgpack_codec::unpack<Arg>(str)));
+          ret = rpc_codec::pack_args(co_await f(rpc_codec::unpack<Arg>(str)));
         } else {
-          ret = msgpack_codec::pack_args(f(msgpack_codec::unpack<Arg>(str)));
+          ret = rpc_codec::pack_args(f(rpc_codec::unpack<Arg>(str)));
         }
       } else {
         if constexpr (is_awaitable_v<R>) {
-          ret = msgpack_codec::pack_args(
-              co_await (*self.*f)(msgpack_codec::unpack<Arg>(str)));
+          ret = rpc_codec::pack_args(
+              co_await (*self.*f)(rpc_codec::unpack<Arg>(str)));
         } else {
-          ret = msgpack_codec::pack_args(
-              (*self.*f)(msgpack_codec::unpack<Arg>(str)));
+          ret = rpc_codec::pack_args((*self.*f)(rpc_codec::unpack<Arg>(str)));
         }
       }
     }
@@ -204,7 +202,7 @@ private:
   template <typename R, typename Args, typename F, typename Self>
   asio::awaitable<void> handle_more_args(std::string_view str, const F &f,
                                          rpc_result &ret, Self *self) {
-    auto tp = msgpack_codec::unpack<Args>(str);
+    auto tp = rpc_codec::unpack<Args>(str);
     if constexpr (std::is_void_v<R>) {
       if constexpr (std::is_void_v<Self>) {
         if constexpr (is_awaitable_v<R>) {
@@ -230,19 +228,19 @@ private:
     } else {
       if constexpr (std::is_void_v<Self>) {
         if constexpr (is_awaitable_v<R>) {
-          ret = msgpack_codec::pack_args(co_await std::apply(f, tp));
+          ret = rpc_codec::pack_args(co_await std::apply(f, tp));
         } else {
-          ret = msgpack_codec::pack_args(std::apply(f, tp));
+          ret = rpc_codec::pack_args(std::apply(f, tp));
         }
       } else {
         if constexpr (is_awaitable_v<R>) {
-          ret = msgpack_codec::pack_args(co_await std::apply(
+          ret = rpc_codec::pack_args(co_await std::apply(
               [self, &f](auto &&...args) {
                 return (*self.*f)(std::forward<decltype(args)>(args)...);
               },
               tp));
         } else {
-          ret = msgpack_codec::pack_args(std::apply(
+          ret = rpc_codec::pack_args(std::apply(
               [self, &f](auto &&...args) {
                 return (*self.*f)(std::forward<decltype(args)>(args)...);
               },
diff --git a/include/rest_rpc/rpc_server.hpp b/include/rest_rpc/rpc_server.hpp
index 9664364..87a10d1 100644
--- a/include/rest_rpc/rpc_server.hpp
+++ b/include/rest_rpc/rpc_server.hpp
@@ -113,8 +113,7 @@ public:
     auto conns = get_connections();
     for (auto &[_, conn] : conns) {
       if (conn->topic_id() == id) {
-        co_await conn->response(msgpack_codec::pack_args(std::forward<T>(t)),
-                                id);
+        co_await conn->response(rpc_codec::pack_args(std::forward<T>(t)), id);
       }
     }
   }
diff --git a/tests/test_rest_rpc.cpp b/tests/test_rest_rpc.cpp
index 4fac2a5..d941216 100644
--- a/tests/test_rest_rpc.cpp
+++ b/tests/test_rest_rpc.cpp
@@ -243,8 +243,8 @@ asio::awaitable<void> test_router() {
   }
 
   {
-    auto s = msgpack_codec::pack_args(1);
-    auto s1 = msgpack_codec::pack_args("test");
+    auto s = rpc_codec::pack_args(1);
+    auto s1 = rpc_codec::pack_args("test");
     auto r = co_await router.route(get_key<round1>(), s);
     auto r1 = co_await router.route(get_key<echo>(), s1);
 
@@ -253,7 +253,7 @@ asio::awaitable<void> test_router() {
     std::cout << "\n";
   }
 
-  auto args = msgpack_codec::pack_args(1, 2);
+  auto args = rpc_codec::pack_args(1, 2);
   std::string_view str(args.data(), args.size());
 
   {
@@ -262,12 +262,12 @@ asio::awaitable<void> test_router() {
     std::cout << "\n";
   }
 
-  auto args1 = msgpack_codec::pack_args("it is a test");
+  auto args1 = rpc_codec::pack_args("it is a test");
   std::string_view str1(args1.data(), args1.size());
 
   {
     auto result = co_await router.route(get_key<&dummy::add>(), str);
-    auto r = msgpack_codec::unpack<int>(result.result);
+    auto r = rpc_codec::unpack<int>(result.result);
     auto result1 = co_await router.route(get_key<&dummy::foo>(), str1);
     CHECK(r == 3);
     CHECK(result1.ec == rpc_errc::ok);
@@ -293,10 +293,10 @@ TEST_CASE("test rpc_connection") {
 
   person p{1, "tom", 20};
 
-  auto buf = msgpack_codec::pack_args(p);
+  auto buf = rpc_codec::pack_args(p);
   auto ret = sync_wait(get_global_executor(),
                        router.route(get_key<get_person>(), buf));
-  auto tp = msgpack_codec::unpack<std::tuple<person>>(ret.data());
+  auto tp = rpc_codec::unpack<std::tuple<person>>(ret.data());
   dummy d{};
   router.register_handler<&dummy::add>(&d);
   auto conn = std::make_shared<rpc_connection>(std::move(socket), conn_id,
@@ -334,12 +334,12 @@ TEST_CASE("test server start") {
 
   static_assert(util::CharArrayRef<char const(&)[5]>);
   static_assert(util::CharArray<const char[5]>);
-  msgpack_codec::pack_args();
-  msgpack_codec::pack_args(1, 2);
-  auto s1 = msgpack_codec::pack_args("test");
-  auto s2 = msgpack_codec::pack_args(std::string_view("test2"));
-  auto s3 = msgpack_codec::pack_args(std::string("test2"));
-  auto s5 = msgpack_codec::pack_args(123);
+  rpc_codec::pack_args();
+  rpc_codec::pack_args(1, 2);
+  auto s1 = rpc_codec::pack_args("test");
+  auto s2 = rpc_codec::pack_args(std::string_view("test2"));
+  auto s3 = rpc_codec::pack_args(std::string("test2"));
+  auto s5 = rpc_codec::pack_args(123);
 
   //  auto future = asio::co_spawn(cl.get_executor(),
   //  cl.connect("127.0.0.1:9005"), asio::use_future); auto conn_ec =
@@ -555,6 +555,40 @@ TEST_CASE("test server address") {
   thd.join();
 }
 
+bool in_user_pack = false;
+bool in_user_unpack = false;
+namespace user_codec {
+// adl lookup in user_codec namespace
+template <typename... Args>
+std::string serialize(rest_adl_tag, Args &&...args) {
+  in_user_pack = true;
+  msgpack::sbuffer buffer(2 * 1024);
+  msgpack::pack(buffer, std::forward_as_tuple(std::forward<Args>(args)...));
+  return std::string(buffer.data(), buffer.size());
+}
+
+template <typename T> T deserialize(rest_adl_tag, std::string_view data) {
+  try {
+    in_user_unpack = true;
+    static msgpack::unpacked msg;
+    msgpack::unpack(msg, data.data(), data.size());
+    return msg.get().as<T>();
+  } catch (...) {
+    return T{};
+  }
+}
+} // namespace user_codec
+
+TEST_CASE("test user codec") {
+  auto buf = rpc_codec::pack_args(
+      std::make_tuple<int, std::string, int>(1, "tom", 20));
+  CHECK(in_user_pack);
+
+  std::string_view str(buf.data(), buf.size());
+  rpc_codec::unpack<std::tuple<int, std::string, int>>(str);
+  CHECK(in_user_unpack);
+}
+
 // doctest comments
 // 'function' : must be 'attribute' - see issue #182
 DOCTEST_MSVC_SUPPRESS_WARNING_WITH_PUSH(4007)