diff --git a/src/assert.cc b/src/assert.cc
index 1edf1e45..eb88120c 100644
--- a/src/assert.cc
+++ b/src/assert.cc
@@ -26,10 +26,10 @@ private:
 
 void on_assert_failed(const char* message)
 {
-    String debug_info = "pid: " + to_string(getpid());
-    write_debug("assert failed: '"_str + message + "' " + debug_info);
+    String debug_info = format("pid: {}", getpid());
+    write_debug(format("assert failed: '{}' ", message, debug_info));
 
-    const auto msg = message + "\n[Debug Infos]\n"_str + debug_info;
+    const auto msg = format("{}\n[Debug Infos]\n{}", message, debug_info);
 #if defined(__CYGWIN__)
     int res = MessageBox(NULL, msg.c_str(), "Kakoune: assert failed",
                          MB_OKCANCEL | MB_ICONERROR);
diff --git a/src/client.cc b/src/client.cc
index dcd575b8..27a56c80 100644
--- a/src/client.cc
+++ b/src/client.cc
@@ -104,11 +104,11 @@ DisplayLine Client::generate_mode_line() const
     Face status_face = get_face("StatusLine");
 
     status.push_back({ context().buffer().display_name(), status_face });
-    status.push_back({ " " + to_string((int)pos.line+1) + ":" + to_string((int)col+1) + " ", status_face });
+    status.push_back({ format(" {}:{} ", pos.line+1, col+1), status_face });
     if (context().buffer().is_modified())
         status.push_back({ "[+]", info_face });
     if (m_input_handler.is_recording())
-        status.push_back({ "[recording ("_str + StringView{m_input_handler.recording_reg()} + ")]", info_face });
+        status.push_back({ format("[recording ({})]", m_input_handler.recording_reg()), info_face });
     if (context().buffer().flags() & Buffer::Flags::New)
         status.push_back({ "[new file]", info_face });
     if (context().user_hooks_support().is_disabled())
@@ -118,7 +118,7 @@ DisplayLine Client::generate_mode_line() const
     status.push_back({ " ", status_face });
     for (auto& atom : m_input_handler.mode_line())
         status.push_back(std::move(atom));
-    status.push_back({ " - " + context().name() + "@[" + Server::instance().session() + "]", status_face });
+    status.push_back({ format(" - {}@[{}]", context().name(), Server::instance().session()), status_face });
 
     return status;
 }
diff --git a/src/client_manager.cc b/src/client_manager.cc
index 26a278ae..ecade79c 100644
--- a/src/client_manager.cc
+++ b/src/client_manager.cc
@@ -19,7 +19,7 @@ String ClientManager::generate_name() const
 {
     for (int i = 0; true; ++i)
     {
-        String name = "unnamed" + to_string(i);
+        String name = format("unnamed{}", i);
         if (validate_client_name(name))
             return name;
     }
diff --git a/src/command_manager.cc b/src/command_manager.cc
index f6e72cbd..736705ca 100644
--- a/src/command_manager.cc
+++ b/src/command_manager.cc
@@ -362,9 +362,8 @@ void CommandManager::execute_single_command(CommandParameters params,
     }
     catch (runtime_error& error)
     {
-        String info = to_string(pos.line+1) + ":" + to_string(pos.column+1) +
-                      ": '" + command_it->first + "' " + error.what();
-        throw runtime_error(std::move(info));
+        throw runtime_error(format("{}:{}: '{}' {}", pos.line+1, pos.column+1,
+                                   command_it->first, error.what()));
     }
 }
 
diff --git a/src/commands.cc b/src/commands.cc
index ccd49079..e1cfcb10 100644
--- a/src/commands.cc
+++ b/src/commands.cc
@@ -834,8 +834,8 @@ const CommandDesc debug_cmd = {
     {
         if (parser[0] == "info")
         {
-            write_debug("pid: " + to_string(getpid()));
-            write_debug("session: " + Server::instance().session());
+            write_debug(format("pid: {}", getpid()));
+            write_debug(format("session: {}", Server::instance().session()));
         }
         else if (parser[0] == "buffers")
         {
@@ -847,7 +847,7 @@ const CommandDesc debug_cmd = {
         {
             write_debug("Options:");
             for (auto& option : context.options().flatten_options())
-                write_debug(" * " + option->name() + ": " + option->get_as_string());
+                write_debug(format(" * {}: {}", option->name(), option->get_as_string()));
         }
         else if (parser[0] == "memory")
         {
@@ -857,11 +857,11 @@ const CommandDesc debug_cmd = {
             {
                 size_t count = domain_allocated_bytes[domain];
                 total += count;
-                write_debug("  "_str + domain_name((MemoryDomain)domain) + ": " + to_string(count));
+                write_debug(format("  {}: {}", domain_name((MemoryDomain)domain), count));
             }
-            write_debug("  Total: " + to_string(total));
+            write_debug(format("  Total: {}", total));
             #if defined(__GLIBC__) || defined(__CYGWIN__)
-            write_debug("  Malloced: " + to_string(mallinfo().uordblks));
+            write_debug(format("  Malloced: {}", mallinfo().uordblks));
             #endif
         }
         else if (parser[0] == "shared-strings")
@@ -869,7 +869,7 @@ const CommandDesc debug_cmd = {
             StringRegistry::instance().debug_stats();
         }
         else
-            throw runtime_error("unknown debug command '" + parser[0] + "'");
+            throw runtime_error(format("unknown debug command '{}'", parser[0]));
     }
 };
 
@@ -890,7 +890,7 @@ const CommandDesc source_cmd = {
         }
         catch (Kakoune::runtime_error& err)
         {
-            write_debug(parser[0] + ":" + err.what());
+            write_debug(format("{}:{}", parser[0], err.what()));
             throw;
         }
     }