diff --git a/CMakeLists.txt b/CMakeLists.txt
index 88637695..f5e422c6 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -618,7 +618,6 @@ list(APPEND LIBDWARFS_COMMON_SRC
   src/dwarfs/internal/string_table.cpp
   src/dwarfs/internal/wcwidth.c
   src/dwarfs/internal/worker_group.cpp
-  src/dwarfs/iolayer.cpp
   src/dwarfs/library_dependencies.cpp
   src/dwarfs/logger.cpp
   src/dwarfs/mmap.cpp
@@ -684,7 +683,10 @@ list(APPEND LIBDWARFS_EXTRACTOR_SRC
 )
 
 list(APPEND LIBDWARFS_TOOL_SRC
+  src/dwarfs/tool/call_sys_main_iolayer.cpp
+  src/dwarfs/tool/iolayer.cpp
   src/dwarfs/tool/safe_main.cpp
+  src/dwarfs/tool/sys_char.cpp
   src/dwarfs/tool/tool.cpp
 )
 
diff --git a/include/dwarfs/tool/call_sys_main_iolayer.h b/include/dwarfs/tool/call_sys_main_iolayer.h
new file mode 100644
index 00000000..7d2d31f4
--- /dev/null
+++ b/include/dwarfs/tool/call_sys_main_iolayer.h
@@ -0,0 +1,38 @@
+/* vim:set ts=2 sw=2 sts=2 et: */
+/**
+ * \author     Marcus Holland-Moritz (github@mhxnet.de)
+ * \copyright  Copyright (c) Marcus Holland-Moritz
+ *
+ * This file is part of dwarfs.
+ *
+ * dwarfs is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dwarfs 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dwarfs.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <span>
+
+#include <dwarfs/tool/sys_char.h>
+
+namespace dwarfs::tool {
+
+struct iolayer;
+
+int call_sys_main_iolayer(std::span<std::string_view> args, iolayer const& iol,
+                          int (*main)(int, sys_char**, iolayer const&));
+
+int call_sys_main_iolayer(std::span<std::string> args, iolayer const& iol,
+                          int (*main)(int, sys_char**, iolayer const&));
+
+} // namespace dwarfs::tool
diff --git a/include/dwarfs/iolayer.h b/include/dwarfs/tool/iolayer.h
similarity index 96%
rename from include/dwarfs/iolayer.h
rename to include/dwarfs/tool/iolayer.h
index 2806ad99..19987d47 100644
--- a/include/dwarfs/iolayer.h
+++ b/include/dwarfs/tool/iolayer.h
@@ -30,6 +30,8 @@ class file_access;
 class os_access;
 class terminal;
 
+namespace tool {
+
 struct iolayer {
   static iolayer const& system_default();
 
@@ -41,4 +43,6 @@ struct iolayer {
   std::ostream& err;
 };
 
+} // namespace tool
+
 } // namespace dwarfs
diff --git a/include/dwarfs/program_options_helpers.h b/include/dwarfs/tool/program_options_helpers.h
similarity index 95%
rename from include/dwarfs/program_options_helpers.h
rename to include/dwarfs/tool/program_options_helpers.h
index 5fffa1b1..dcd02924 100644
--- a/include/dwarfs/program_options_helpers.h
+++ b/include/dwarfs/tool/program_options_helpers.h
@@ -25,7 +25,7 @@
 
 #include <dwarfs/types.h>
 
-namespace dwarfs {
+namespace dwarfs::tool {
 
 #ifdef _WIN32
 template <typename T>
@@ -39,4 +39,4 @@ auto po_sys_value(T* v) {
 }
 #endif
 
-} // namespace dwarfs
+} // namespace dwarfs::tool
diff --git a/include/dwarfs/tool/sys_char.h b/include/dwarfs/tool/sys_char.h
new file mode 100644
index 00000000..c3ccded3
--- /dev/null
+++ b/include/dwarfs/tool/sys_char.h
@@ -0,0 +1,41 @@
+/* vim:set ts=2 sw=2 sts=2 et: */
+/**
+ * \author     Marcus Holland-Moritz (github@mhxnet.de)
+ * \copyright  Copyright (c) Marcus Holland-Moritz
+ *
+ * This file is part of dwarfs.
+ *
+ * dwarfs is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dwarfs 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dwarfs.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <string>
+
+namespace dwarfs::tool {
+
+#ifdef _WIN32
+#define SYS_MAIN wmain
+using sys_char = wchar_t;
+using sys_string = std::wstring;
+#else
+#define SYS_MAIN main
+using sys_char = char;
+using sys_string = std::string;
+#endif
+
+std::string sys_string_to_string(sys_string const& in);
+sys_string string_to_sys_string(std::string const& in);
+
+} // namespace dwarfs::tool
diff --git a/include/dwarfs/tool/tool.h b/include/dwarfs/tool/tool.h
index 84faa53a..2ddec7ec 100644
--- a/include/dwarfs/tool/tool.h
+++ b/include/dwarfs/tool/tool.h
@@ -26,6 +26,8 @@
 
 #include <boost/program_options.hpp>
 
+#include <dwarfs/tool/call_sys_main_iolayer.h>
+
 #ifdef DWARFS_BUILTIN_MANPAGE
 #include <dwarfs/tool/manpage.h>
 #endif
diff --git a/include/dwarfs/tool/tool_fwd.h b/include/dwarfs/tool/tool_fwd.h
new file mode 100644
index 00000000..c098a8c2
--- /dev/null
+++ b/include/dwarfs/tool/tool_fwd.h
@@ -0,0 +1,44 @@
+/* vim:set ts=2 sw=2 sts=2 et: */
+/**
+ * \author     Marcus Holland-Moritz (github@mhxnet.de)
+ * \copyright  Copyright (c) Marcus Holland-Moritz
+ *
+ * This file is part of dwarfs.
+ *
+ * dwarfs is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dwarfs 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dwarfs.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <iosfwd>
+#include <span>
+#include <string>
+#include <string_view>
+
+#include <dwarfs/tool/sys_char.h>
+#include <dwarfs/tool/tool_fwd.h>
+
+namespace dwarfs::tool {
+
+struct iolayer;
+
+}
+
+#define DWARFS_TOOL_MAIN_DECL(tool_name)                                       \
+  namespace dwarfs::tool {                                                     \
+  int tool_name##_main(std::span<std::string> args, iolayer const& iol);       \
+  int tool_name##_main(std::span<std::string_view> args, iolayer const& iol);  \
+  int tool_name##_main(int argc, sys_char** argv, iolayer const& iol);         \
+  int tool_name##_main(int argc, sys_char** argv);                             \
+  }
diff --git a/include/dwarfs/types.h b/include/dwarfs/types.h
index 0914000f..abc8953e 100644
--- a/include/dwarfs/types.h
+++ b/include/dwarfs/types.h
@@ -22,21 +22,9 @@
 #pragma once
 
 #include <cstdint>
-#include <iostream>
-#include <string>
 
 namespace dwarfs {
 
 using file_off_t = int64_t;
 
-#ifdef _WIN32
-#define SYS_MAIN wmain
-using sys_char = wchar_t;
-using sys_string = std::wstring;
-#else
-#define SYS_MAIN main
-using sys_char = char;
-using sys_string = std::string;
-#endif
-
 } // namespace dwarfs
diff --git a/include/dwarfs/util.h b/include/dwarfs/util.h
index 1b830b04..ac8b9b53 100644
--- a/include/dwarfs/util.h
+++ b/include/dwarfs/util.h
@@ -34,8 +34,6 @@
 
 namespace dwarfs {
 
-struct iolayer;
-
 std::string time_with_unit(double sec);
 std::string time_with_unit(std::chrono::nanoseconds ns);
 std::string size_with_unit(size_t size);
@@ -53,15 +51,6 @@ inline std::string u8string_to_string(std::u8string const& in) {
   return std::string(reinterpret_cast<char const*>(in.data()), in.size());
 }
 
-std::string sys_string_to_string(sys_string const& in);
-sys_string string_to_sys_string(std::string const& in);
-
-int call_sys_main_iolayer(std::span<std::string_view> args, iolayer const& iol,
-                          int (*main)(int, sys_char**, iolayer const&));
-
-int call_sys_main_iolayer(std::span<std::string> args, iolayer const& iol,
-                          int (*main)(int, sys_char**, iolayer const&));
-
 size_t utf8_display_width(char const* p, size_t len);
 size_t utf8_display_width(std::string const& str);
 void utf8_truncate(std::string& str, size_t len);
diff --git a/include/dwarfs_tool_main.h b/include/dwarfs_tool_main.h
index e139e3e3..8ba8d4fc 100644
--- a/include/dwarfs_tool_main.h
+++ b/include/dwarfs_tool_main.h
@@ -21,40 +21,10 @@
 
 #pragma once
 
-#include <iosfwd>
-#include <span>
-#include <string>
-#include <string_view>
+#include <dwarfs/tool/tool_fwd.h>
 
-#include <dwarfs/types.h>
-
-namespace dwarfs {
-
-struct iolayer;
-
-int mkdwarfs_main(std::span<std::string> args, iolayer const& iol);
-int mkdwarfs_main(std::span<std::string_view> args, iolayer const& iol);
-int mkdwarfs_main(int argc, sys_char** argv, iolayer const& iol);
-int mkdwarfs_main(int argc, sys_char** argv);
-
-int dwarfsck_main(std::span<std::string> args, iolayer const& iol);
-int dwarfsck_main(std::span<std::string_view> args, iolayer const& iol);
-int dwarfsck_main(int argc, sys_char** argv, iolayer const& iol);
-int dwarfsck_main(int argc, sys_char** argv);
-
-int dwarfsextract_main(std::span<std::string> args, iolayer const& iol);
-int dwarfsextract_main(std::span<std::string_view> args, iolayer const& iol);
-int dwarfsextract_main(int argc, sys_char** argv, iolayer const& iol);
-int dwarfsextract_main(int argc, sys_char** argv);
-
-int dwarfsbench_main(std::span<std::string> args, iolayer const& iol);
-int dwarfsbench_main(std::span<std::string_view> args, iolayer const& iol);
-int dwarfsbench_main(int argc, sys_char** argv, iolayer const& iol);
-int dwarfsbench_main(int argc, sys_char** argv);
-
-int dwarfs_main(std::span<std::string> args, iolayer const& iol);
-int dwarfs_main(std::span<std::string_view> args, iolayer const& iol);
-int dwarfs_main(int argc, sys_char** argv, iolayer const& iol);
-int dwarfs_main(int argc, sys_char** argv);
-
-} // namespace dwarfs
+DWARFS_TOOL_MAIN_DECL(mkdwarfs)
+DWARFS_TOOL_MAIN_DECL(dwarfsck)
+DWARFS_TOOL_MAIN_DECL(dwarfsextract)
+DWARFS_TOOL_MAIN_DECL(dwarfsbench)
+DWARFS_TOOL_MAIN_DECL(dwarfs)
diff --git a/src/dwarfs.cpp b/src/dwarfs.cpp
index c65c6f0b..ca84ec6f 100644
--- a/src/dwarfs.cpp
+++ b/src/dwarfs.cpp
@@ -22,7 +22,7 @@
 #include <dwarfs/tool/safe_main.h>
 #include <dwarfs_tool_main.h>
 
-int SYS_MAIN(int argc, dwarfs::sys_char** argv) {
+int SYS_MAIN(int argc, dwarfs::tool::sys_char** argv) {
   return dwarfs::tool::safe_main(
-      [&] { return dwarfs::dwarfs_main(argc, argv); });
+      [&] { return dwarfs::tool::dwarfs_main(argc, argv); });
 }
diff --git a/src/dwarfs/tool/call_sys_main_iolayer.cpp b/src/dwarfs/tool/call_sys_main_iolayer.cpp
new file mode 100644
index 00000000..098fd64e
--- /dev/null
+++ b/src/dwarfs/tool/call_sys_main_iolayer.cpp
@@ -0,0 +1,58 @@
+/* vim:set ts=2 sw=2 sts=2 et: */
+/**
+ * \author     Marcus Holland-Moritz (github@mhxnet.de)
+ * \copyright  Copyright (c) Marcus Holland-Moritz
+ *
+ * This file is part of dwarfs.
+ *
+ * dwarfs is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dwarfs 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dwarfs.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <vector>
+
+#include <dwarfs/tool/call_sys_main_iolayer.h>
+
+extern "C" int dwarfs_wcwidth(int ucs);
+
+namespace dwarfs::tool {
+
+namespace {
+
+template <typename T>
+int call_sys_main_iolayer_impl(std::span<T> args, iolayer const& iol,
+                               int (*main)(int, sys_char**, iolayer const&)) {
+  std::vector<sys_string> argv;
+  std::vector<sys_char*> argv_ptrs;
+  argv.reserve(args.size());
+  argv_ptrs.reserve(args.size());
+  for (auto const& arg : args) {
+    argv.emplace_back(string_to_sys_string(std::string(arg)));
+    argv_ptrs.emplace_back(argv.back().data());
+  }
+  return main(argv_ptrs.size(), argv_ptrs.data(), iol);
+}
+
+} // namespace
+
+int call_sys_main_iolayer(std::span<std::string_view> args, iolayer const& iol,
+                          int (*main)(int, sys_char**, iolayer const&)) {
+  return call_sys_main_iolayer_impl(args, iol, main);
+}
+
+int call_sys_main_iolayer(std::span<std::string> args, iolayer const& iol,
+                          int (*main)(int, sys_char**, iolayer const&)) {
+  return call_sys_main_iolayer_impl(args, iol, main);
+}
+
+} // namespace dwarfs::tool
diff --git a/src/dwarfs/iolayer.cpp b/src/dwarfs/tool/iolayer.cpp
similarity index 93%
rename from src/dwarfs/iolayer.cpp
rename to src/dwarfs/tool/iolayer.cpp
index 229a9621..58a41871 100644
--- a/src/dwarfs/iolayer.cpp
+++ b/src/dwarfs/tool/iolayer.cpp
@@ -23,11 +23,11 @@
 
 #include <dwarfs/file_access.h>
 #include <dwarfs/file_access_generic.h>
-#include <dwarfs/iolayer.h>
 #include <dwarfs/os_access_generic.h>
 #include <dwarfs/terminal.h>
+#include <dwarfs/tool/iolayer.h>
 
-namespace dwarfs {
+namespace dwarfs::tool {
 
 iolayer const& iolayer::system_default() {
   static iolayer const iol{
@@ -41,4 +41,4 @@ iolayer const& iolayer::system_default() {
   return iol;
 }
 
-} // namespace dwarfs
+} // namespace dwarfs::tool
diff --git a/src/dwarfs/tool/sys_char.cpp b/src/dwarfs/tool/sys_char.cpp
new file mode 100644
index 00000000..eb3e36a2
--- /dev/null
+++ b/src/dwarfs/tool/sys_char.cpp
@@ -0,0 +1,57 @@
+/* vim:set ts=2 sw=2 sts=2 et: */
+/**
+ * \author     Marcus Holland-Moritz (github@mhxnet.de)
+ * \copyright  Copyright (c) Marcus Holland-Moritz
+ *
+ * This file is part of dwarfs.
+ *
+ * dwarfs is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * dwarfs 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with dwarfs.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include <algorithm>
+
+#if __has_include(<utf8cpp/utf8.h>)
+#include <utf8cpp/utf8.h>
+#else
+#include <utf8.h>
+#endif
+
+#include <dwarfs/tool/sys_char.h>
+
+namespace dwarfs::tool {
+
+std::string sys_string_to_string(sys_string const& in) {
+#ifdef _WIN32
+  std::u16string tmp(in.size(), 0);
+  std::transform(in.begin(), in.end(), tmp.begin(),
+                 [](sys_char c) { return static_cast<char16_t>(c); });
+  return utf8::utf16to8(tmp);
+#else
+  return in;
+#endif
+}
+
+sys_string string_to_sys_string(std::string const& in) {
+#ifdef _WIN32
+  auto tmp = utf8::utf8to16(in);
+  sys_string rv(tmp.size(), 0);
+  std::transform(tmp.begin(), tmp.end(), rv.begin(),
+                 [](char16_t c) { return static_cast<sys_char>(c); });
+  return rv;
+#else
+  return in;
+#endif
+}
+
+} // namespace dwarfs::tool
diff --git a/src/dwarfs/tool/tool.cpp b/src/dwarfs/tool/tool.cpp
index 6f3c9087..bd221aab 100644
--- a/src/dwarfs/tool/tool.cpp
+++ b/src/dwarfs/tool/tool.cpp
@@ -28,8 +28,8 @@
 #include <dwarfs/version.h>
 
 #ifdef DWARFS_BUILTIN_MANPAGE
-#include <dwarfs/iolayer.h>
 #include <dwarfs/terminal.h>
+#include <dwarfs/tool/iolayer.h>
 #include <dwarfs/tool/pager.h>
 #include <dwarfs/tool/render_manpage.h>
 #endif
diff --git a/src/dwarfs/util.cpp b/src/dwarfs/util.cpp
index f132fdb6..ae0c7dd5 100644
--- a/src/dwarfs/util.cpp
+++ b/src/dwarfs/util.cpp
@@ -60,20 +60,6 @@ inline std::string trimmed(std::string in) {
   return in;
 }
 
-template <typename T>
-int call_sys_main_iolayer_impl(std::span<T> args, iolayer const& iol,
-                               int (*main)(int, sys_char**, iolayer const&)) {
-  std::vector<sys_string> argv;
-  std::vector<sys_char*> argv_ptrs;
-  argv.reserve(args.size());
-  argv_ptrs.reserve(args.size());
-  for (auto const& arg : args) {
-    argv.emplace_back(string_to_sys_string(std::string(arg)));
-    argv_ptrs.emplace_back(argv.back().data());
-  }
-  return main(argv_ptrs.size(), argv_ptrs.data(), iol);
-}
-
 } // namespace
 
 std::string size_with_unit(size_t size) {
@@ -205,39 +191,6 @@ file_off_t parse_image_offset(std::string const& str) {
   return off.value();
 }
 
-std::string sys_string_to_string(sys_string const& in) {
-#ifdef _WIN32
-  std::u16string tmp(in.size(), 0);
-  std::transform(in.begin(), in.end(), tmp.begin(),
-                 [](sys_char c) { return static_cast<char16_t>(c); });
-  return utf8::utf16to8(tmp);
-#else
-  return in;
-#endif
-}
-
-sys_string string_to_sys_string(std::string const& in) {
-#ifdef _WIN32
-  auto tmp = utf8::utf8to16(in);
-  sys_string rv(tmp.size(), 0);
-  std::transform(tmp.begin(), tmp.end(), rv.begin(),
-                 [](char16_t c) { return static_cast<sys_char>(c); });
-  return rv;
-#else
-  return in;
-#endif
-}
-
-int call_sys_main_iolayer(std::span<std::string_view> args, iolayer const& iol,
-                          int (*main)(int, sys_char**, iolayer const&)) {
-  return call_sys_main_iolayer_impl(args, iol, main);
-}
-
-int call_sys_main_iolayer(std::span<std::string> args, iolayer const& iol,
-                          int (*main)(int, sys_char**, iolayer const&)) {
-  return call_sys_main_iolayer_impl(args, iol, main);
-}
-
 size_t utf8_display_width(char const* p, size_t len) {
   char const* const e = p + len;
   size_t rv = 0;
diff --git a/src/dwarfs_main.cpp b/src/dwarfs_main.cpp
index a99a5210..5565661d 100644
--- a/src/dwarfs_main.cpp
+++ b/src/dwarfs_main.cpp
@@ -87,7 +87,6 @@
 #include <dwarfs/file_stat.h>
 #include <dwarfs/filesystem_v2.h>
 #include <dwarfs/fstypes.h>
-#include <dwarfs/iolayer.h>
 #include <dwarfs/iovec_read_buf.h>
 #include <dwarfs/library_dependencies.h>
 #include <dwarfs/logger.h>
@@ -97,6 +96,8 @@
 #include <dwarfs/performance_monitor.h>
 #include <dwarfs/scope_exit.h>
 #include <dwarfs/string.h>
+#include <dwarfs/tool/call_sys_main_iolayer.h>
+#include <dwarfs/tool/iolayer.h>
 #include <dwarfs/tool/tool.h>
 #include <dwarfs/util.h>
 #include <dwarfs/version.h>
@@ -140,7 +141,7 @@ FARPROC WINAPI delay_hook(unsigned dliNotify, PDelayLoadInfo pdli) {
 extern "C" const PfnDliHook __pfnDliFailureHook2 = delay_hook;
 #endif
 
-namespace dwarfs {
+namespace dwarfs::tool {
 
 namespace {
 
@@ -1664,4 +1665,4 @@ int dwarfs_main(std::span<std::string_view> args, iolayer const& iol) {
   return call_sys_main_iolayer(args, iol, dwarfs_main);
 }
 
-} // namespace dwarfs
+} // namespace dwarfs::tool
diff --git a/src/dwarfsbench.cpp b/src/dwarfsbench.cpp
index 4f8ac162..a3cfe174 100644
--- a/src/dwarfsbench.cpp
+++ b/src/dwarfsbench.cpp
@@ -22,7 +22,7 @@
 #include <dwarfs/tool/safe_main.h>
 #include <dwarfs_tool_main.h>
 
-int SYS_MAIN(int argc, dwarfs::sys_char** argv) {
+int SYS_MAIN(int argc, dwarfs::tool::sys_char** argv) {
   return dwarfs::tool::safe_main(
-      [&] { return dwarfs::dwarfsbench_main(argc, argv); });
+      [&] { return dwarfs::tool::dwarfsbench_main(argc, argv); });
 }
diff --git a/src/dwarfsbench_main.cpp b/src/dwarfsbench_main.cpp
index e2720b28..1d7677d7 100644
--- a/src/dwarfsbench_main.cpp
+++ b/src/dwarfsbench_main.cpp
@@ -27,19 +27,20 @@
 #include <dwarfs/file_stat.h>
 #include <dwarfs/filesystem_v2.h>
 #include <dwarfs/fstypes.h>
-#include <dwarfs/iolayer.h>
 #include <dwarfs/library_dependencies.h>
 #include <dwarfs/logger.h>
 #include <dwarfs/mmap.h>
 #include <dwarfs/options.h>
 #include <dwarfs/thread_pool.h>
+#include <dwarfs/tool/call_sys_main_iolayer.h>
+#include <dwarfs/tool/iolayer.h>
 #include <dwarfs/tool/tool.h>
 #include <dwarfs/util.h>
 #include <dwarfs_tool_main.h>
 
 namespace po = boost::program_options;
 
-namespace dwarfs {
+namespace dwarfs::tool {
 
 int dwarfsbench_main(int argc, sys_char** argv, iolayer const& iol) {
   std::string filesystem, cache_size_str, lock_mode_str, decompress_ratio_str;
@@ -145,4 +146,4 @@ int dwarfsbench_main(std::span<std::string_view> args, iolayer const& iol) {
   return call_sys_main_iolayer(args, iol, dwarfsbench_main);
 }
 
-} // namespace dwarfs
+} // namespace dwarfs::tool
diff --git a/src/dwarfsck.cpp b/src/dwarfsck.cpp
index 740405d8..03cf4a55 100644
--- a/src/dwarfsck.cpp
+++ b/src/dwarfsck.cpp
@@ -22,7 +22,7 @@
 #include <dwarfs/tool/safe_main.h>
 #include <dwarfs_tool_main.h>
 
-int SYS_MAIN(int argc, dwarfs::sys_char** argv) {
+int SYS_MAIN(int argc, dwarfs::tool::sys_char** argv) {
   return dwarfs::tool::safe_main(
-      [&] { return dwarfs::dwarfsck_main(argc, argv); });
+      [&] { return dwarfs::tool::dwarfsck_main(argc, argv); });
 }
diff --git a/src/dwarfsck_main.cpp b/src/dwarfsck_main.cpp
index aaa13855..3b7b566f 100644
--- a/src/dwarfsck_main.cpp
+++ b/src/dwarfsck_main.cpp
@@ -39,19 +39,20 @@
 #include <dwarfs/error.h>
 #include <dwarfs/file_access.h>
 #include <dwarfs/filesystem_v2.h>
-#include <dwarfs/iolayer.h>
 #include <dwarfs/library_dependencies.h>
 #include <dwarfs/logger.h>
 #include <dwarfs/mmap.h>
 #include <dwarfs/options.h>
 #include <dwarfs/os_access.h>
-#include <dwarfs/program_options_helpers.h>
 #include <dwarfs/thread_pool.h>
+#include <dwarfs/tool/call_sys_main_iolayer.h>
+#include <dwarfs/tool/iolayer.h>
+#include <dwarfs/tool/program_options_helpers.h>
 #include <dwarfs/tool/tool.h>
 #include <dwarfs/util.h>
 #include <dwarfs_tool_main.h>
 
-namespace dwarfs {
+namespace dwarfs::tool {
 
 namespace po = boost::program_options;
 
@@ -376,4 +377,4 @@ int dwarfsck_main(std::span<std::string_view> args, iolayer const& iol) {
   return call_sys_main_iolayer(args, iol, dwarfsck_main);
 }
 
-} // namespace dwarfs
+} // namespace dwarfs::tool
diff --git a/src/dwarfsextract.cpp b/src/dwarfsextract.cpp
index bec62cd5..ce40317e 100644
--- a/src/dwarfsextract.cpp
+++ b/src/dwarfsextract.cpp
@@ -22,7 +22,7 @@
 #include <dwarfs/tool/safe_main.h>
 #include <dwarfs_tool_main.h>
 
-int SYS_MAIN(int argc, dwarfs::sys_char** argv) {
+int SYS_MAIN(int argc, dwarfs::tool::sys_char** argv) {
   return dwarfs::tool::safe_main(
-      [&] { return dwarfs::dwarfsextract_main(argc, argv); });
+      [&] { return dwarfs::tool::dwarfsextract_main(argc, argv); });
 }
diff --git a/src/dwarfsextract_main.cpp b/src/dwarfsextract_main.cpp
index f1e9ce0d..4112d0ca 100644
--- a/src/dwarfsextract_main.cpp
+++ b/src/dwarfsextract_main.cpp
@@ -28,22 +28,23 @@
 
 #include <dwarfs/filesystem_extractor.h>
 #include <dwarfs/filesystem_v2.h>
-#include <dwarfs/iolayer.h>
 #include <dwarfs/library_dependencies.h>
 #include <dwarfs/logger.h>
 #include <dwarfs/mmap.h>
 #include <dwarfs/options.h>
 #include <dwarfs/os_access.h>
 #include <dwarfs/performance_monitor.h>
-#include <dwarfs/program_options_helpers.h>
 #include <dwarfs/string.h>
+#include <dwarfs/tool/call_sys_main_iolayer.h>
+#include <dwarfs/tool/iolayer.h>
+#include <dwarfs/tool/program_options_helpers.h>
 #include <dwarfs/tool/tool.h>
 #include <dwarfs/util.h>
 #include <dwarfs_tool_main.h>
 
 namespace po = boost::program_options;
 
-namespace dwarfs {
+namespace dwarfs::tool {
 
 namespace {
 
@@ -241,4 +242,4 @@ int dwarfsextract_main(std::span<std::string_view> args, iolayer const& iol) {
   return call_sys_main_iolayer(args, iol, dwarfsextract_main);
 }
 
-} // namespace dwarfs
+} // namespace dwarfs::tool
diff --git a/src/mkdwarfs.cpp b/src/mkdwarfs.cpp
index 0f68244a..b42640d8 100644
--- a/src/mkdwarfs.cpp
+++ b/src/mkdwarfs.cpp
@@ -22,7 +22,7 @@
 #include <dwarfs/tool/safe_main.h>
 #include <dwarfs_tool_main.h>
 
-int SYS_MAIN(int argc, dwarfs::sys_char** argv) {
+int SYS_MAIN(int argc, dwarfs::tool::sys_char** argv) {
   return dwarfs::tool::safe_main(
-      [&] { return dwarfs::mkdwarfs_main(argc, argv); });
+      [&] { return dwarfs::tool::mkdwarfs_main(argc, argv); });
 }
diff --git a/src/mkdwarfs_main.cpp b/src/mkdwarfs_main.cpp
index 4ca3b357..aed0bcf2 100644
--- a/src/mkdwarfs_main.cpp
+++ b/src/mkdwarfs_main.cpp
@@ -70,20 +70,21 @@
 #include <dwarfs/filter_debug.h>
 #include <dwarfs/fragment_order_parser.h>
 #include <dwarfs/integral_value_parser.h>
-#include <dwarfs/iolayer.h>
 #include <dwarfs/library_dependencies.h>
 #include <dwarfs/logger.h>
 #include <dwarfs/match.h>
 #include <dwarfs/mmap.h>
 #include <dwarfs/options.h>
 #include <dwarfs/os_access.h>
-#include <dwarfs/program_options_helpers.h>
 #include <dwarfs/scanner.h>
 #include <dwarfs/script.h>
 #include <dwarfs/segmenter_factory.h>
 #include <dwarfs/string.h>
 #include <dwarfs/terminal.h>
 #include <dwarfs/thread_pool.h>
+#include <dwarfs/tool/call_sys_main_iolayer.h>
+#include <dwarfs/tool/iolayer.h>
+#include <dwarfs/tool/program_options_helpers.h>
 #include <dwarfs/tool/tool.h>
 #include <dwarfs/util.h>
 #include <dwarfs/writer_progress.h>
@@ -91,7 +92,7 @@
 
 namespace po = boost::program_options;
 
-namespace dwarfs {
+namespace dwarfs::tool {
 
 namespace {
 
@@ -1414,4 +1415,4 @@ int mkdwarfs_main(std::span<std::string_view> args, iolayer const& iol) {
   return call_sys_main_iolayer(args, iol, mkdwarfs_main);
 }
 
-} // namespace dwarfs
+} // namespace dwarfs::tool
diff --git a/src/pxattr.cpp b/src/pxattr.cpp
index 622676b1..6153be12 100644
--- a/src/pxattr.cpp
+++ b/src/pxattr.cpp
@@ -23,11 +23,11 @@
 
 #include <boost/program_options.hpp>
 
-#include <dwarfs/program_options_helpers.h>
-#include <dwarfs/types.h>
+#include <dwarfs/tool/program_options_helpers.h>
+#include <dwarfs/tool/sys_char.h>
 #include <dwarfs/xattr.h>
 
-namespace dwarfs {
+namespace dwarfs::tool {
 
 namespace po = boost::program_options;
 namespace fs = std::filesystem;
@@ -124,8 +124,8 @@ int pxattr_main(int argc, sys_char** argv) {
   return 0;
 }
 
-} // namespace dwarfs
+} // namespace dwarfs::tool
 
-int SYS_MAIN(int argc, dwarfs::sys_char** argv) {
-  return dwarfs::pxattr_main(argc, argv);
+int SYS_MAIN(int argc, dwarfs::tool::sys_char** argv) {
+  return dwarfs::tool::pxattr_main(argc, argv);
 }
diff --git a/src/universal.cpp b/src/universal.cpp
index 59f04b6a..acc5fb07 100644
--- a/src/universal.cpp
+++ b/src/universal.cpp
@@ -20,6 +20,7 @@
  */
 
 #include <algorithm>
+#include <cctype>
 #include <cstdlib>
 #include <filesystem>
 #include <iostream>
@@ -35,12 +36,11 @@
 
 #include <dwarfs/tool/safe_main.h>
 #include <dwarfs/tool/tool.h>
-#include <dwarfs/util.h>
 #include <dwarfs_tool_main.h>
 
 namespace {
 
-using namespace dwarfs;
+using namespace dwarfs::tool;
 
 #ifdef _WIN32
 #define EXE_EXT ".exe"
@@ -66,7 +66,7 @@ int SYS_MAIN(int argc, sys_char** argv) {
   if (auto ext = path.extension().string(); ext.empty() || ext == EXE_EXT) {
     auto stem = path.stem().string();
     if (auto it = functions.find(stem); it != functions.end()) {
-      return tool::safe_main([&] { return it->second(argc, argv); });
+      return safe_main([&] { return it->second(argc, argv); });
     }
   }
 
@@ -80,7 +80,7 @@ int SYS_MAIN(int argc, sys_char** argv) {
         argv_copy.reserve(argc - 1);
         argv_copy.emplace_back(argv[0]);
         std::copy(argv + 2, argv + argc, std::back_inserter(argv_copy));
-        return tool::safe_main(
+        return safe_main(
             [&] { return it->second(argc - 1, argv_copy.data()); });
       }
     }
@@ -92,7 +92,7 @@ int SYS_MAIN(int argc, sys_char** argv) {
                ranges::to<std::string>;
 
   // clang-format off
-  std::cout << tool::tool_header("dwarfs-universal")
+  std::cout << tool_header("dwarfs-universal")
             << "Command line options:\n"
             << "  --tool=<name>                     "
                  "which tool to run; available tools are:\n"
diff --git a/test/test_helpers.h b/test/test_helpers.h
index 9b569c28..aecc052f 100644
--- a/test/test_helpers.h
+++ b/test/test_helpers.h
@@ -41,10 +41,10 @@
 #include <dwarfs/entry_interface.h>
 #include <dwarfs/file_access.h>
 #include <dwarfs/file_stat.h>
-#include <dwarfs/iolayer.h>
 #include <dwarfs/os_access.h>
 #include <dwarfs/script.h>
 #include <dwarfs/terminal.h>
+#include <dwarfs/tool/iolayer.h>
 
 #if defined(__has_feature)
 #if __has_feature(address_sanitizer)
@@ -302,7 +302,7 @@ class test_iolayer {
                std::shared_ptr<file_access const> fa);
   ~test_iolayer();
 
-  iolayer const& get();
+  tool::iolayer const& get();
 
   std::string out() const;
   std::string err() const;
@@ -327,7 +327,7 @@ class test_iolayer {
   std::istringstream in_;
   std::ostringstream out_;
   std::ostringstream err_;
-  std::unique_ptr<iolayer> iol_;
+  std::unique_ptr<tool::iolayer> iol_;
   std::shared_ptr<terminal const> real_term_;
 };
 
diff --git a/test/test_iolayer.cpp b/test/test_iolayer.cpp
index 2cfc1e90..a1559e4c 100644
--- a/test/test_iolayer.cpp
+++ b/test/test_iolayer.cpp
@@ -315,10 +315,10 @@ test_iolayer::test_iolayer(std::shared_ptr<os_access const> os,
 
 test_iolayer::~test_iolayer() = default;
 
-iolayer const& test_iolayer::get() {
+tool::iolayer const& test_iolayer::get() {
   if (!iol_) {
     if (real_term_) {
-      iol_ = std::make_unique<iolayer>(iolayer{
+      iol_ = std::make_unique<tool::iolayer>(tool::iolayer{
           .os = os_,
           .term = real_term_,
           .file = fa_,
@@ -327,7 +327,7 @@ iolayer const& test_iolayer::get() {
           .err = std::cerr,
       });
     } else {
-      iol_ = std::make_unique<iolayer>(iolayer{
+      iol_ = std::make_unique<tool::iolayer>(tool::iolayer{
           .os = os_,
           .term = term_,
           .file = fa_,
diff --git a/test/tool_main_test.cpp b/test/tool_main_test.cpp
index f8c3631b..73dea123 100644
--- a/test/tool_main_test.cpp
+++ b/test/tool_main_test.cpp
@@ -58,6 +58,8 @@ using namespace dwarfs;
 
 namespace fs = std::filesystem;
 
+using tool::iolayer;
+
 namespace {
 
 // TODO: this is a workaround for older Clang versions
@@ -167,7 +169,7 @@ auto constexpr default_fs_opts = filesystem_options{
 class mkdwarfs_tester : public tester_common {
  public:
   mkdwarfs_tester(std::shared_ptr<test::os_access_mock> pos)
-      : tester_common(mkdwarfs_main, "mkdwarfs", std::move(pos)) {}
+      : tester_common(tool::mkdwarfs_main, "mkdwarfs", std::move(pos)) {}
 
   mkdwarfs_tester()
       : mkdwarfs_tester(test::os_access_mock::create_test_instance()) {}
@@ -322,7 +324,7 @@ build_test_image(std::vector<std::string> extra_args = {},
 class dwarfsck_tester : public tester_common {
  public:
   dwarfsck_tester(std::shared_ptr<test::os_access_mock> pos)
-      : tester_common(dwarfsck_main, "dwarfsck", std::move(pos)) {}
+      : tester_common(tool::dwarfsck_main, "dwarfsck", std::move(pos)) {}
 
   dwarfsck_tester()
       : dwarfsck_tester(std::make_shared<test::os_access_mock>()) {}
@@ -342,7 +344,8 @@ class dwarfsck_tester : public tester_common {
 class dwarfsextract_tester : public tester_common {
  public:
   dwarfsextract_tester(std::shared_ptr<test::os_access_mock> pos)
-      : tester_common(dwarfsextract_main, "dwarfsextract", std::move(pos)) {}
+      : tester_common(tool::dwarfsextract_main, "dwarfsextract",
+                      std::move(pos)) {}
 
   dwarfsextract_tester()
       : dwarfsextract_tester(std::make_shared<test::os_access_mock>()) {}