diff --git a/src/assert.cc b/src/assert.cc
index b193f595e..eeb4b36e0 100644
--- a/src/assert.cc
+++ b/src/assert.cc
@@ -38,7 +38,7 @@ bool notify_fatal_error(const String& msg)
         return true;
     }
 #elif defined(__linux__)
-    auto cmd = "xmessage -buttons 'quit:0,ignore:1' '" + msg + "'";
+    auto cmd = format("xmessage -buttons 'quit:0,ignore:1' '{}'", msg);
     if (system(cmd.c_str()) == 1)
         return true;
 #endif
diff --git a/src/client.cc b/src/client.cc
index 71e8c29f3..a7d3b59aa 100644
--- a/src/client.cc
+++ b/src/client.cc
@@ -175,7 +175,7 @@ void Client::reload_buffer()
     kak_assert(buffer.flags() & Buffer::Flags::File);
     Buffer* buf = create_buffer_from_file(buffer.name());
     kak_assert(buf == &buffer);
-    context().print_status({ "'" + buffer.display_name() + "' reloaded",
+    context().print_status({ format("'{}' reloaded", buffer.display_name()),
                              get_face("Information") });
 }
 
@@ -189,12 +189,12 @@ void Client::on_buffer_reload_key(Key key)
     {
         // reread timestamp in case the file was modified again
         buffer.set_fs_timestamp(get_fs_timestamp(buffer.name()));
-        print_status({ "'" + buffer.display_name() + "' kept",
+        print_status({ format("'{}' kept", buffer.display_name()),
                        get_face("Information") });
     }
     else
     {
-        print_status({ "'" + key_to_str(key) + "' is not a valid choice",
+        print_status({ format("'{}' is not a valid choice", key_to_str(key)),
                        get_face("Error") });
         m_input_handler.on_next_key(KeymapMode::None, [this](Key key, Context&){ on_buffer_reload_key(key); });
         return;
@@ -233,9 +233,10 @@ void Client::check_if_buffer_needs_reloading()
     if (reload == Ask)
     {
         m_ui->info_show(
-            "reload '" + buffer.display_name() + "' ?",
-            "'" + buffer.display_name() + "' was modified externally\n"
-            "press <ret> or y to reload, <esc> or n to keep",
+            format("reload '{}' ?", buffer.display_name()),
+            format("'{}' was modified externally\n"
+                   "press <ret> or y to reload, <esc> or n to keep",
+                   buffer.display_name()),
             CharCoord{}, get_face("Information"), InfoStyle::Prompt);
 
         m_buffer_reload_dialog_opened = true;
diff --git a/src/client_manager.cc b/src/client_manager.cc
index ecade79c5..5e4978e62 100644
--- a/src/client_manager.cc
+++ b/src/client_manager.cc
@@ -110,8 +110,9 @@ void ClientManager::ensure_no_client_uses_buffer(Buffer& buffer)
             continue;
 
         if (client->context().is_editing())
-            throw runtime_error("client '" + client->context().name() + "' is inserting in '" +
-                                buffer.display_name() + "'");
+            throw runtime_error(format("client '{}' is inserting in buffer '{}'",
+                                       client->context().name(),
+                                       buffer.display_name()));
 
         // change client context to edit the first buffer which is not the
         // specified one. As BufferManager stores buffer according to last
@@ -150,7 +151,7 @@ Client& ClientManager::get_client(StringView name)
 {
     if (Client* client = get_client_ifp(name))
         return *client;
-    throw runtime_error("no client named: " + name);
+    throw runtime_error(format("no client named '{}'", name));
 }
 
 void ClientManager::redraw_clients() const
diff --git a/src/commands.cc b/src/commands.cc
index 65328f01d..e496124a4 100644
--- a/src/commands.cc
+++ b/src/commands.cc
@@ -45,7 +45,7 @@ Buffer* open_fifo(StringView name, StringView filename, bool scroll)
     int fd = open(parse_filename(filename).c_str(), O_RDONLY | O_NONBLOCK);
     fcntl(fd, F_SETFD, FD_CLOEXEC);
     if (fd < 0)
-       throw runtime_error("unable to open " + filename);
+       throw runtime_error(format("unable to open '{}'", filename));
 
     return create_fifo_buffer(name.str(), fd, scroll);
 }
@@ -109,7 +109,7 @@ Scope& get_scope(StringView scope, const Context& context)
 {
     if (auto s = get_scope_ifp(scope, context))
         return *s;
-    throw runtime_error("error: no such scope " + scope);
+    throw runtime_error(format("error: no such scope '{}'", scope));
 }
 
 struct CommandDesc
@@ -158,9 +158,10 @@ void edit(const ParametersParser& parser, Context& context)
             if (not buffer)
             {
                 if (parser.get_switch("existing"))
-                    throw runtime_error("unable to open " + name);
+                    throw runtime_error(format("unable to open '{}'", name));
 
-                context.print_status({ "new file " + name, get_face("StatusLine") });
+                context.print_status({ format("new file '{}'", name),
+                                       get_face("StatusLine") });
                 buffer = new Buffer(name, Buffer::Flags::File | Buffer::Flags::New);
             }
         }
@@ -444,10 +445,10 @@ void delete_buffer(const ParametersParser& parser, Context& context)
     BufferManager& manager = BufferManager::instance();
     Buffer& buffer = parser.positional_count() == 0 ? context.buffer() : manager.get_buffer(parser[0]);
     if (not force and (buffer.flags() & Buffer::Flags::File) and buffer.is_modified())
-        throw runtime_error("buffer " + buffer.name() + " is modified");
+        throw runtime_error(format("buffer '{}' is modified", buffer.name()));
 
     if (manager.count() == 1)
-        throw runtime_error("buffer " + buffer.name() + " is the last one");
+        throw runtime_error(format("buffer '{}' is the last one", buffer.name()));
 
     manager.delete_buffer(buffer);
 }
@@ -486,7 +487,7 @@ const CommandDesc namebuf_cmd = {
     [](const ParametersParser& parser, Context& context)
     {
         if (not context.buffer().set_name(parser[0]))
-            throw runtime_error("unable to change buffer name to " + parser[0]);
+            throw runtime_error(format("unable to change buffer name to '{}'", parser[0]));
     }
 };
 
@@ -573,7 +574,7 @@ const CommandDesc add_highlighter_cmd = {
             HighlighterRegistry& registry = HighlighterRegistry::instance();
             auto it = registry.find(params[0]);
             if (it != registry.end())
-                return params[0] + ":\n" + indent(it->second.docstring);
+                return format("{}:\n{}", params[0], indent(it->second.docstring));
         }
         return "";
     },
@@ -593,7 +594,7 @@ const CommandDesc add_highlighter_cmd = {
                                  : context.window().highlighters();
         auto it = registry.find(name);
         if (it == registry.end())
-            throw runtime_error("No such highlighter factory '" + name + "'");
+            throw runtime_error(format("No such highlighter factory '{}'", name));
         group.add_child(it->second.factory(highlighter_params));
     }
 };
@@ -712,7 +713,7 @@ void define_command(const ParametersParser& parser, Context& context)
     auto& cm = CommandManager::instance();
 
     if (cm.command_defined(cmd_name) and not parser.get_switch("allow-override"))
-        throw runtime_error("command '" + cmd_name + "' already defined");
+        throw runtime_error(format("command '{}' already defined", cmd_name));
 
     CommandFlags flags = CommandFlags::None;
     if (parser.get_switch("hidden"))
@@ -978,7 +979,7 @@ const CommandDesc set_option_cmd = {
             OptionManager& options = get_scope(params[0], context).options();
             const String& docstring = options[params[1]].docstring();
             if (not docstring.empty())
-                return params[1] + ": " + docstring;
+                return format("{}: {}", params[1], docstring);
         }
         catch (runtime_error&) {}
         return "";
@@ -1063,7 +1064,7 @@ const CommandDesc declare_option_cmd = {
         else if (parser[0] == "line-flag-list")
             opt = &reg.declare_option<Vector<LineAndFlag, MemoryDomain::Options>>(parser[1], docstring, {}, flags);
         else
-            throw runtime_error("unknown type " + parser[0]);
+            throw runtime_error(format("unknown type {}", parser[0]));
 
         if (parser.positional_count() == 3)
             opt->set_from_string(parser[2]);
@@ -1080,7 +1081,7 @@ KeymapMode parse_keymap_mode(const String& str)
     if (prefix_match("view", str))   return KeymapMode::View;
     if (prefix_match("user", str))   return KeymapMode::User;
 
-    throw runtime_error("unknown keymap mode '" + str + "'");
+    throw runtime_error(format("unknown keymap mode '{}'", str));
 }
 
 const CommandDesc map_key_cmd = {
@@ -1282,9 +1283,7 @@ const CommandDesc eval_string_cmd = {
     [](const ParametersParser& parser, Context& context)
     {
         context_wrap(parser, context, [](const ParametersParser& parser, Context& context) {
-            String command;
-            for (auto& param : parser)
-                command += param + " ";
+            String command = join(parser, ' ', false);
             CommandManager::instance().execute(command, context);
         });
     }
@@ -1427,7 +1426,7 @@ const CommandDesc info_cmd = {
                     else if (*placement == "below")
                         style = InfoStyle::InlineBelow;
                     else
-                        throw runtime_error("invalid placement " + *placement);
+                        throw runtime_error(format("invalid placement '{}'", *placement));
                 }
             }
             auto title = parser.get_switch("title").value_or(StringView{});
@@ -1502,7 +1501,7 @@ const CommandDesc set_client_name_cmd = {
         if (ClientManager::instance().validate_client_name(parser[0]))
             context.set_name(parser[0]);
         else if (context.name() != parser[0])
-            throw runtime_error("client name '" + parser[0] + "' is not unique");
+            throw runtime_error(format("client name '{}' is not unique", parser[0]));
     }
 };
 
@@ -1545,7 +1544,7 @@ const CommandDesc change_working_directory_cmd = {
     [](const ParametersParser& parser, Context&)
     {
         if (chdir(parse_filename(parser[0]).c_str()) != 0)
-            throw runtime_error("cannot change to directory " + parser[0]);
+            throw runtime_error(format("cannot change to directory '{}'", parser[0]));
     }
 };
 
diff --git a/src/face_registry.cc b/src/face_registry.cc
index 8f2cfbea6..1a972852f 100644
--- a/src/face_registry.cc
+++ b/src/face_registry.cc
@@ -28,7 +28,7 @@ static Face parse_face(StringView facedesc)
                 case 'b': res.attributes |= Attribute::Bold; break;
                 case 'B': res.attributes |= Attribute::Blink; break;
                 case 'd': res.attributes |= Attribute::Dim; break;
-                default: throw runtime_error("unknown face attribute '" + StringView(*attr_it) + "'");
+                default: throw runtime_error(format("unknown face attribute '{}'", StringView{*attr_it}));
             }
         }
     }
@@ -51,12 +51,12 @@ void FaceRegistry::register_alias(const String& name, const String& facedesc,
                                   bool override)
 {
     if (not override and m_aliases.find(name) != m_aliases.end())
-        throw runtime_error("alias '" + name + "' already defined");
+        throw runtime_error(format("alias '{}' already defined", name));
 
     if (name.empty() or is_color_name(name) or
         std::any_of(name.begin(), name.end(),
                     [](char c){ return not isalnum(c); }))
-        throw runtime_error("invalid alias name");
+        throw runtime_error(format("invalid alias name: '{}'", name));
 
     FaceOrAlias& alias = m_aliases[name];
     auto it = m_aliases.find(facedesc);
diff --git a/src/file.hh b/src/file.hh
index 68e401c95..6f018e55d 100644
--- a/src/file.hh
+++ b/src/file.hh
@@ -14,7 +14,7 @@ struct file_access_error : runtime_error
 public:
     file_access_error(StringView filename,
                       StringView error_desc)
-        : runtime_error(filename + ": " + error_desc) {}
+        : runtime_error(format("{}: {}", filename, error_desc)) {}
 };
 
 struct file_not_found : file_access_error
diff --git a/src/highlighter_group.cc b/src/highlighter_group.cc
index 8a9d364f8..3224cc8a0 100644
--- a/src/highlighter_group.cc
+++ b/src/highlighter_group.cc
@@ -15,7 +15,7 @@ void HighlighterGroup::highlight(const Context& context, HighlightFlags flags,
 void HighlighterGroup::add_child(HighlighterAndId&& hl)
 {
     if (m_highlighters.contains(hl.first))
-        throw runtime_error("duplicate id: " + hl.first);
+        throw runtime_error(format("duplicate id: '{}'", hl.first));
 
     m_highlighters.append(std::move(hl));
 }
@@ -31,7 +31,7 @@ Highlighter& HighlighterGroup::get_child(StringView path)
     StringView id(path.begin(), sep_it);
     auto it = m_highlighters.find(id);
     if (it == m_highlighters.end())
-        throw child_not_found("no such id: " + id);
+        throw child_not_found(format("no such id: '{}'", id));
     if (sep_it == path.end())
         return *it->second;
     else
diff --git a/src/hook_manager.cc b/src/hook_manager.cc
index d7879c614..da57a1dab 100644
--- a/src/hook_manager.cc
+++ b/src/hook_manager.cc
@@ -60,8 +60,8 @@ void HookManager::run_hook(StringView hook_name,
         }
         catch (runtime_error& err)
         {
-            write_debug("error running hook " + hook_name + "/" +
-                        hook.first + ": " + err.what());
+            write_debug(format("error running hook {}/{}: {}",
+                               hook_name, hook.first, err.what()));
         }
     }
 }
diff --git a/src/input_handler.cc b/src/input_handler.cc
index f5e9440d0..0d4f74121 100644
--- a/src/input_handler.cc
+++ b/src/input_handler.cc
@@ -1010,7 +1010,7 @@ public:
     {
         auto num_sel = context().selections().size();
         return {AtomList{ { "insert ", Face(Color::Green) },
-                          { to_string(num_sel) + " sel", Face(Color::Blue) } }};
+                          { format( "{} sel", num_sel), Face(Color::Blue) } }};
     }
 
     KeymapMode keymap_mode() const override { return KeymapMode::Insert; }
diff --git a/src/insert_completer.cc b/src/insert_completer.cc
index 30be039cd..248636767 100644
--- a/src/insert_completer.cc
+++ b/src/insert_completer.cc
@@ -56,7 +56,7 @@ void option_from_string(StringView str, InsertCompleterDesc& opt)
         opt.param = Optional<String>{};
         return;
     }
-    throw runtime_error("invalid completer description: " + str);
+    throw runtime_error(format("invalid completer description: '{}'", str));
 }
 
 namespace
diff --git a/src/normal.cc b/src/normal.cc
index ef4231bf9..f2b983dff 100644
--- a/src/normal.cc
+++ b/src/normal.cc
@@ -211,11 +211,11 @@ void goto_commands(Context& context, NormalParams params)
 
                 String path = find_file(filename, paths);
                 if (path.empty())
-                    throw runtime_error("unable to find file '" + filename + "'");
+                    throw runtime_error(format("unable to find file '{}'", filename));
 
                 Buffer* buffer = create_buffer_from_file(path);
                 if (buffer == nullptr)
-                    throw runtime_error("unable to open file '" + path + "'");
+                    throw runtime_error(format("unable to open file '{}'", path));
 
                 if (buffer != &context.buffer())
                 {
diff --git a/src/option_manager.hh b/src/option_manager.hh
index ec56cf107..23a801f3c 100644
--- a/src/option_manager.hh
+++ b/src/option_manager.hh
@@ -168,7 +168,7 @@ template<typename T> const T& Option::get() const
 {
     auto* typed_opt = dynamic_cast<const TypedOption<T>*>(this);
     if (not typed_opt)
-        throw runtime_error("option " + name() + " is not of type " + typeid(T).name());
+        throw runtime_error(format("option '{}' is not of type '{}'", name(), typeid(T).name()));
     return typed_opt->get();
 }
 
@@ -176,7 +176,7 @@ template<typename T> void Option::set(const T& val)
 {
     auto* typed_opt = dynamic_cast<TypedOption<T>*>(this);
     if (not typed_opt)
-        throw runtime_error("option " + name() + " is not of type " + typeid(T).name());
+        throw runtime_error(format("option '{}' is not of type '{}'", name(), typeid(T).name()));
     return typed_opt->set(val);
 }
 
@@ -208,7 +208,7 @@ public:
         {
             if ((*it)->is_of_type<T>() and (*it)->flags() == flags)
                 return **it;
-            throw runtime_error("option " + name + " already declared with different type or flags");
+            throw runtime_error(format("option '{}' already declared with different type or flags", name));
         }
         m_descs.emplace_back(new OptionDesc{name, docstring, flags});
         opts.emplace_back(new TypedOption<T>{m_global_manager, *m_descs.back(), value});
diff --git a/src/option_types.hh b/src/option_types.hh
index 265d3c234..ae960261f 100644
--- a/src/option_types.hh
+++ b/src/option_types.hh
@@ -217,7 +217,7 @@ inline void option_from_string(StringView str, YesNoAsk& opt)
     else if (str == "ask")
         opt = Ask;
     else
-        throw runtime_error("invalid value '" + str + "', expected yes, no or ask");
+        throw runtime_error(format("invalid value '{}', expected yes, no or ask", str));
 }
 
 }
diff --git a/src/parameters_parser.hh b/src/parameters_parser.hh
index 827eacf9e..79f4f7022 100644
--- a/src/parameters_parser.hh
+++ b/src/parameters_parser.hh
@@ -21,13 +21,13 @@ struct parameter_error : public runtime_error
 struct unknown_option : public parameter_error
 {
     unknown_option(StringView name)
-        : parameter_error("unknown option '" + name + "'") {}
+        : parameter_error(format("unknown option '{}'", name)) {}
 };
 
 struct missing_option_value: public parameter_error
 {
     missing_option_value(StringView name)
-        : parameter_error("missing value for option '" + name + "'") {}
+        : parameter_error(format("missing value for option '{}'", name)) {}
 };
 
 struct wrong_argument_count : public parameter_error
diff --git a/src/register_manager.cc b/src/register_manager.cc
index 7990c13bd..27ca47bdb 100644
--- a/src/register_manager.cc
+++ b/src/register_manager.cc
@@ -68,7 +68,7 @@ Register& RegisterManager::operator[](StringView reg)
     };
     auto it = reg_names.find(reg);
     if (it == reg_names.end())
-        throw runtime_error("no such register: " + reg);
+        throw runtime_error(format("no such register: '{}'", reg));
     return (*this)[it->second];
 }
 
diff --git a/src/remote.cc b/src/remote.cc
index 05da041cc..207abfb16 100644
--- a/src/remote.cc
+++ b/src/remote.cc
@@ -287,14 +287,12 @@ RemoteUI::RemoteUI(int socket)
                                m_input_callback(mode);
                        })
 {
-    write_debug("remote client connected: " +
-                to_string(m_socket_watcher.fd()));
+    write_debug(format("remote client connected: {}", m_socket_watcher.fd()));
 }
 
 RemoteUI::~RemoteUI()
 {
-    write_debug("remote client disconnected: " +
-                to_string(m_socket_watcher.fd()));
+    write_debug(format("remote client disconnected: {}", m_socket_watcher.fd()));
     m_socket_watcher.close_fd();
 }
 
@@ -421,7 +419,7 @@ static sockaddr_un session_addr(StringView session)
 {
     sockaddr_un addr;
     addr.sun_family = AF_UNIX;
-    strncpy(addr.sun_path, ("/tmp/kak-" + session).c_str(),
+    strncpy(addr.sun_path, format("/tmp/kak-{}", session).c_str(),
             sizeof(addr.sun_path) - 1);
     return addr;
 }
@@ -585,8 +583,8 @@ private:
                 }
                 catch (runtime_error& e)
                 {
-                    write_debug("error running command '" + m_buffer +
-                                "' : " + e.what());
+                    write_debug(format("error running command '{}': {}",
+                                       m_buffer, e.what()));
                 }
                 catch (client_removed&) {}
                 close(socket);
@@ -645,7 +643,7 @@ Server::Server(String session_name)
 
 void Server::close_session()
 {
-    unlink(("/tmp/kak-" + m_session).c_str());
+    unlink(format("/tmp/kak-{}", m_session).c_str());
     m_listener->close_fd();
     m_listener.reset();
 }
diff --git a/src/remote.hh b/src/remote.hh
index bb59270dd..60d616194 100644
--- a/src/remote.hh
+++ b/src/remote.hh
@@ -17,7 +17,7 @@ struct peer_disconnected {};
 struct connection_failed : runtime_error
 {
     connection_failed(StringView filename)
-        : runtime_error{"connect to " + filename + " failed"}
+        : runtime_error{format("connect to {} failed", filename)}
     {}
 };
 
diff --git a/src/selectors.hh b/src/selectors.hh
index f5cf8504a..a2810d035 100644
--- a/src/selectors.hh
+++ b/src/selectors.hh
@@ -259,7 +259,7 @@ Selection find_next_match(const Buffer& buffer, const Selection& sel, const Rege
             captures.emplace_back(match.first, match.second);
     }
     if (not found or begin == buffer.end())
-        throw runtime_error("'" + regex.str() + "': no matches found");
+        throw runtime_error(format("'{}': no matches found", regex.str()));
 
     end = (begin == end) ? end : utf8::previous(end, begin);
     if (direction == Backward)