diff --git a/AGENTS.md b/AGENTS.md
index 5447cfb..1c64343 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -40,7 +40,14 @@
 - Place opening braces on the **same line** as class, method, and namespace declarations.
 - Do not use `using namespace`; qualify names with their namespaces (e.g., `std::`).
 - Project headers come **before** system headers in include lists.
-- Each header file must start with `#pragma once` followed by an include guard of the form `_SIMPLE_NAMED_PIPE_*_HPP_INCLUDED`.
+- Each project-owned C/C++ header must start with `#pragma once` followed by a
+  non-reserved include guard derived from the project prefix and header path:
+  `SIMPLE_NAMED_PIPE_HEADER_<PATH>_<FILE>_<EXT>_INCLUDED`.
+- Do not use guard names that start with an underscore, start with an underscore
+  followed by an uppercase letter, or contain a double underscore.
+- Implementation fragments such as `.ipp`, `.inl`, or `.tpp` may remain
+  unguarded if they are only included from already guarded headers and are not
+  intended for direct inclusion.
 
 ## Constants and Macros
 
@@ -67,4 +74,3 @@
   - `build:` – build system or dependency updates
   - `ci:` – CI/CD configuration changes
   - `chore:` – tasks that do not affect production code
-
diff --git a/include/SimpleNamedPipe/NamedPipeClient.hpp b/include/SimpleNamedPipe/NamedPipeClient.hpp
index db76f81..2cce715 100644
--- a/include/SimpleNamedPipe/NamedPipeClient.hpp
+++ b/include/SimpleNamedPipe/NamedPipeClient.hpp
@@ -1,6 +1,6 @@
 #pragma once
-#ifndef _SIMPLE_NAMED_PIPE_CLIENT_HPP_INCLUDED
-#define _SIMPLE_NAMED_PIPE_CLIENT_HPP_INCLUDED
+#ifndef SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPECLIENT_HPP_INCLUDED
+#define SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPECLIENT_HPP_INCLUDED
 
 /// \file NamedPipeClient.hpp
 /// \brief Synchronous named pipe client for tests and lightweight integrations.
@@ -132,4 +132,4 @@ namespace SimpleNamedPipe {
 #include "NamedPipeClient/NamedPipeClient.ipp"
 #endif
 
-#endif // _SIMPLE_NAMED_PIPE_CLIENT_HPP_INCLUDED
+#endif // SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPECLIENT_HPP_INCLUDED
diff --git a/include/SimpleNamedPipe/NamedPipeClient/ClientConfig.hpp b/include/SimpleNamedPipe/NamedPipeClient/ClientConfig.hpp
index 9efd76d..b3d35d6 100644
--- a/include/SimpleNamedPipe/NamedPipeClient/ClientConfig.hpp
+++ b/include/SimpleNamedPipe/NamedPipeClient/ClientConfig.hpp
@@ -1,6 +1,6 @@
 #pragma once
-#ifndef _SIMPLE_NAMED_PIPE_CLIENT_CONFIG_HPP_INCLUDED
-#define _SIMPLE_NAMED_PIPE_CLIENT_CONFIG_HPP_INCLUDED
+#ifndef SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPECLIENT_CLIENTCONFIG_HPP_INCLUDED
+#define SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPECLIENT_CLIENTCONFIG_HPP_INCLUDED
 
 /// \file ClientConfig.hpp
 /// \brief Configuration for the named pipe client.
@@ -33,4 +33,4 @@ namespace SimpleNamedPipe {
 
 } // namespace SimpleNamedPipe
 
-#endif // _SIMPLE_NAMED_PIPE_CLIENT_CONFIG_HPP_INCLUDED
+#endif // SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPECLIENT_CLIENTCONFIG_HPP_INCLUDED
diff --git a/include/SimpleNamedPipe/NamedPipeServer.hpp b/include/SimpleNamedPipe/NamedPipeServer.hpp
index 0108683..370799e 100644
--- a/include/SimpleNamedPipe/NamedPipeServer.hpp
+++ b/include/SimpleNamedPipe/NamedPipeServer.hpp
@@ -1,6 +1,6 @@
 #pragma once
-#ifndef _SIMPLE_NAMED_PIPE_SERVER_HPP_INCLUDED
-#define _SIMPLE_NAMED_PIPE_SERVER_HPP_INCLUDED
+#ifndef SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_HPP_INCLUDED
+#define SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_HPP_INCLUDED
 
 /// \file NamedPipeServer.hpp
 /// \brief Server implementation for managing named pipes
@@ -182,4 +182,4 @@ namespace SimpleNamedPipe {
 #include "NamedPipeServer/NamedPipeServer.ipp"
 #endif
 
-#endif // _SIMPLE_NAMED_PIPE_SERVER_HPP_INCLUDED
+#endif // SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_HPP_INCLUDED
diff --git a/include/SimpleNamedPipe/NamedPipeServer/Connection.hpp b/include/SimpleNamedPipe/NamedPipeServer/Connection.hpp
index d68b5ed..492f5ac 100644
--- a/include/SimpleNamedPipe/NamedPipeServer/Connection.hpp
+++ b/include/SimpleNamedPipe/NamedPipeServer/Connection.hpp
@@ -1,6 +1,6 @@
 #pragma once
-#ifndef _SIMPLE_NAMED_PIPE_CONNECTION_HPP_INCLUDED
-#define _SIMPLE_NAMED_PIPE_CONNECTION_HPP_INCLUDED
+#ifndef SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_CONNECTION_HPP_INCLUDED
+#define SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_CONNECTION_HPP_INCLUDED
 
 /// \file Connection.hpp
 /// \brief Defines the Connection class for managing individual named pipe connections.
@@ -79,4 +79,4 @@ namespace SimpleNamedPipe {
 
 } // namespace SimpleNamedPipe
 
-#endif // _SIMPLE_NAMED_PIPE_CONNECTION_HPP_INCLUDED
+#endif // SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_CONNECTION_HPP_INCLUDED
diff --git a/include/SimpleNamedPipe/NamedPipeServer/IConnection.hpp b/include/SimpleNamedPipe/NamedPipeServer/IConnection.hpp
index 87648b6..55c2e4e 100644
--- a/include/SimpleNamedPipe/NamedPipeServer/IConnection.hpp
+++ b/include/SimpleNamedPipe/NamedPipeServer/IConnection.hpp
@@ -1,6 +1,6 @@
 #pragma once
-#ifndef _SIMPLE_NAMED_PIPE_SERVER_ICONNECTION_HPP_INCLUDED
-#define _SIMPLE_NAMED_PIPE_SERVER_ICONNECTION_HPP_INCLUDED
+#ifndef SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_ICONNECTION_HPP_INCLUDED
+#define SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_ICONNECTION_HPP_INCLUDED
 
 /// \file IConnection.hpp
 /// \brief Interface for server-side connection operations.
@@ -34,4 +34,4 @@ namespace SimpleNamedPipe {
 
 };
 
-#endif // _SIMPLE_NAMED_PIPE_SERVER_ICONNECTION_HPP_INCLUDED
+#endif // SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_ICONNECTION_HPP_INCLUDED
diff --git a/include/SimpleNamedPipe/NamedPipeServer/ServerConfig.hpp b/include/SimpleNamedPipe/NamedPipeServer/ServerConfig.hpp
index 07fa59f..ec889e9 100644
--- a/include/SimpleNamedPipe/NamedPipeServer/ServerConfig.hpp
+++ b/include/SimpleNamedPipe/NamedPipeServer/ServerConfig.hpp
@@ -1,6 +1,6 @@
 #pragma once
-#ifndef _SIMPLE_NAMED_PIPE_SERVER_CONFIG_HPP_INCLUDED
-#define _SIMPLE_NAMED_PIPE_SERVER_CONFIG_HPP_INCLUDED
+#ifndef SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_SERVERCONFIG_HPP_INCLUDED
+#define SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_SERVERCONFIG_HPP_INCLUDED
 
 /// \file ServerConfig.hpp
 /// \brief Configuration for the named pipe server.
@@ -36,4 +36,4 @@ namespace SimpleNamedPipe {
     };
 }
 
-#endif // _SIMPLE_NAMED_PIPE_SERVER_CONFIG_HPP_INCLUDED
+#endif // SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_SERVERCONFIG_HPP_INCLUDED
diff --git a/include/SimpleNamedPipe/NamedPipeServer/ServerEvent.hpp b/include/SimpleNamedPipe/NamedPipeServer/ServerEvent.hpp
index cc943bf..e76e018 100644
--- a/include/SimpleNamedPipe/NamedPipeServer/ServerEvent.hpp
+++ b/include/SimpleNamedPipe/NamedPipeServer/ServerEvent.hpp
@@ -1,6 +1,6 @@
 #pragma once
-#ifndef _SIMPLE_NAMED_PIPE_SERVER_EVENT_HPP_INCLUDED
-#define _SIMPLE_NAMED_PIPE_SERVER_EVENT_HPP_INCLUDED
+#ifndef SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_SERVEREVENT_HPP_INCLUDED
+#define SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_SERVEREVENT_HPP_INCLUDED
 
 #include <system_error>
 #include <string>
@@ -76,4 +76,4 @@ namespace SimpleNamedPipe {
 
 } // namespace SimpleNamedPipe
 
-#endif // _SIMPLE_NAMED_PIPE_SERVER_EVENT_HPP_INCLUDED
+#endif // SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_SERVEREVENT_HPP_INCLUDED
diff --git a/include/SimpleNamedPipe/NamedPipeServer/ServerEventHandler.hpp b/include/SimpleNamedPipe/NamedPipeServer/ServerEventHandler.hpp
index 3eec306..792f3a8 100644
--- a/include/SimpleNamedPipe/NamedPipeServer/ServerEventHandler.hpp
+++ b/include/SimpleNamedPipe/NamedPipeServer/ServerEventHandler.hpp
@@ -1,6 +1,6 @@
 #pragma once
-#ifndef _SIMPLE_NAMED_PIPE_SERVER_EVENT_HANDLER_HPP_INCLUDED
-#define _SIMPLE_NAMED_PIPE_SERVER_EVENT_HANDLER_HPP_INCLUDED
+#ifndef SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_SERVEREVENTHANDLER_HPP_INCLUDED
+#define SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_SERVEREVENTHANDLER_HPP_INCLUDED
 
 /// \file ServerEventHandler.hpp
 /// \brief Base interface for handling server events.
@@ -23,4 +23,4 @@ namespace SimpleNamedPipe {
 
 }; // namespace SimpleNamedPipe
 
-#endif // _SIMPLE_NAMED_PIPE_SERVER_EVENT_HANDLER_HPP_INCLUDED
+#endif // SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_SERVEREVENTHANDLER_HPP_INCLUDED
diff --git a/include/SimpleNamedPipe/NamedPipeServer/errors.hpp b/include/SimpleNamedPipe/NamedPipeServer/errors.hpp
index f1e3e90..8ee50fd 100644
--- a/include/SimpleNamedPipe/NamedPipeServer/errors.hpp
+++ b/include/SimpleNamedPipe/NamedPipeServer/errors.hpp
@@ -1,6 +1,6 @@
 #pragma once
-#ifndef _SIMPLE_NAMED_PIPE_SERVER_ERRORS_HPP_INCLUDED
-#define _SIMPLE_NAMED_PIPE_SERVER_ERRORS_HPP_INCLUDED
+#ifndef SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_ERRORS_HPP_INCLUDED
+#define SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_ERRORS_HPP_INCLUDED
 
 /// \file errors.hpp
 /// \brief Error codes and category for NamedPipeServer
@@ -75,4 +75,4 @@ namespace std {
     struct is_error_code_enum<SimpleNamedPipe::NamedPipeErrc> : true_type {};
 }
 
-#endif // _SIMPLE_NAMED_PIPE_SERVER_ERRORS_HPP_INCLUDED
+#endif // SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_NAMEDPIPESERVER_ERRORS_HPP_INCLUDED
diff --git a/include/SimpleNamedPipe/detail/string_utils.hpp b/include/SimpleNamedPipe/detail/string_utils.hpp
index c3370a1..a92b92d 100644
--- a/include/SimpleNamedPipe/detail/string_utils.hpp
+++ b/include/SimpleNamedPipe/detail/string_utils.hpp
@@ -1,6 +1,6 @@
 #pragma once
-#ifndef _SIMPLE_NAMED_PIPE_DETAIL_STRING_UTILS_HPP_INCLUDED
-#define _SIMPLE_NAMED_PIPE_DETAIL_STRING_UTILS_HPP_INCLUDED
+#ifndef SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_DETAIL_STRING_UTILS_HPP_INCLUDED
+#define SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_DETAIL_STRING_UTILS_HPP_INCLUDED
 
 #include <windows.h>
 
@@ -58,4 +58,4 @@ namespace detail {
 } // namespace detail
 } // namespace SimpleNamedPipe
 
-#endif // _SIMPLE_NAMED_PIPE_DETAIL_STRING_UTILS_HPP_INCLUDED
+#endif // SIMPLE_NAMED_PIPE_HEADER_SIMPLENAMEDPIPE_DETAIL_STRING_UTILS_HPP_INCLUDED