diff --git a/src/buffer.cc b/src/buffer.cc
index fe162486..93808fd6 100644
--- a/src/buffer.cc
+++ b/src/buffer.cc
@@ -532,19 +532,6 @@ ByteCoord Buffer::last_modification_coord() const
 
 String Buffer::debug_description() const
 {
-    String res = display_name() + "\n";
-
-    res += "  Flags: ";
-    if (m_flags & Flags::File)
-        res += "File (" + name() + ") ";
-    if (m_flags & Flags::New)
-        res += "New ";
-    if (m_flags & Flags::Fifo)
-        res += "Fifo ";
-    if (m_flags & Flags::NoUndo)
-        res += "NoUndo ";
-    res += "\n";
-
     size_t content_size = 0;
     for (auto& line : m_lines)
         content_size += (int)line->strview().length();
@@ -554,9 +541,13 @@ String Buffer::debug_description() const
         additional_size += undo_group.size() * sizeof(Modification);
     additional_size += m_changes.size() * sizeof(Change);
 
-    res += "  Used mem: content=" + to_string(content_size) +
-           " additional=" + to_string(additional_size) + "\n";
-    return res;
+    return format("{}\nFlags: {}{}{}{}\nUsed mem: content={} additional={}\n",
+                  display_name(),
+                  (m_flags & Flags::File) ? "File (" + name() + ") " : "",
+                  (m_flags & Flags::New) ? "New " : "",
+                  (m_flags & Flags::Fifo) ? "Fifo " : "",
+                  (m_flags & Flags::NoUndo) ? "NoUndo " : "",
+                  content_size, additional_size);
 }
 
 }
diff --git a/src/command_manager.cc b/src/command_manager.cc
index 62018bc8..f6e72cbd 100644
--- a/src/command_manager.cc
+++ b/src/command_manager.cc
@@ -36,7 +36,7 @@ void CommandManager::register_command(String command_name,
 struct parse_error : runtime_error
 {
     parse_error(StringView error)
-        : runtime_error{"parse error: " + error} {}
+        : runtime_error{format("parse error: {}", error)} {}
 };
 
 namespace
@@ -125,7 +125,7 @@ String get_until_delimiter(StringView base, ByteCount& pos,
 struct unknown_expand : parse_error
 {
     unknown_expand(StringView name)
-        : parse_error{"unknown expand '" + name + "'"} {}
+        : parse_error{format("unknown expand '{}'", name)} {}
 };
 
 template<bool throw_on_invalid>
@@ -169,14 +169,6 @@ void skip_blanks_and_comments(StringView base, ByteCount& pos)
     }
 }
 
-struct unterminated_string : parse_error
-{
-    unterminated_string(StringView open, StringView close, int nest = 0)
-        : parse_error{"unterminated string '" + open + "..." + close + "'" +
-                      (nest > 0 ? "(nesting: " + to_string(nest) + ")" : "")}
-    {}
-};
-
 template<bool throw_on_unterminated>
 Token parse_percent_token(StringView line, ByteCount& pos)
 {
@@ -187,8 +179,8 @@ Token parse_percent_token(StringView line, ByteCount& pos)
     StringView type_name = line.substr(type_start, pos - type_start);
 
     if (throw_on_unterminated and pos == length)
-        throw parse_error{"expected a string delimiter after '%" +
-                          type_name + "'"};
+        throw parse_error{format("expected a string delimiter after '%{}'",
+                                 type_name)};
 
     Token::Type type = token_type<throw_on_unterminated>(type_name);
     static const UnorderedMap<char, char> matching_delimiters = {
@@ -205,8 +197,9 @@ Token parse_percent_token(StringView line, ByteCount& pos)
         String token = get_until_delimiter(line, pos, opening_delimiter,
                                            closing_delimiter);
         if (throw_on_unterminated and pos == length)
-            throw unterminated_string("%" + type_name + StringView{opening_delimiter},
-                                      closing_delimiter, 0);
+            throw parse_error{format("unterminated string '%{}{}...{}'",
+                                     type_name, opening_delimiter,
+                                     closing_delimiter)};
         return {type, token_start, pos, std::move(token)};
     }
     else
@@ -237,7 +230,7 @@ TokenList parse(StringView line)
             token_start = ++pos;
             String token = get_until_delimiter(line, pos, delimiter);
             if (throw_on_unterminated and pos == length)
-                throw unterminated_string(delimiter, delimiter);
+                throw parse_error{format("unterminated string {0}...{0}", delimiter)};
             result.emplace_back(delimiter == '"' ? Token::Type::RawEval
                                                  : Token::Type::Raw,
                                 token_start, pos, std::move(token));
diff --git a/src/file.cc b/src/file.cc
index a3cc8bbb..dfffb043 100644
--- a/src/file.cc
+++ b/src/file.cc
@@ -77,7 +77,7 @@ String real_path(StringView filename)
         {
             if (non_existing.empty())
                 return res;
-            return res + "/"_str + non_existing;
+            return format("{}/{}", res, non_existing);
         }
 
         auto it = find(existing.rbegin(), existing.rend(), '/');
diff --git a/src/insert_completer.cc b/src/insert_completer.cc
index 073347a9..24c0c27d 100644
--- a/src/insert_completer.cc
+++ b/src/insert_completer.cc
@@ -430,7 +430,7 @@ bool InsertCompleter::try_complete(CompleteFunc complete_func)
     }
     catch (runtime_error& e)
     {
-        write_debug("error while trying to run completer: "_str + e.what());
+        write_debug(format("error while trying to run completer: {}", e.what()));
         return false;
     }
     if (not m_completions.is_valid())
diff --git a/src/main.cc b/src/main.cc
index 2a0d0b58..94a9ce8a 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -117,15 +117,15 @@ void register_env_vars()
             [](StringView name, const Context& context)
             { auto& sel = context.selections().main();
               auto beg = sel.min();
-              return to_string(beg.line + 1) + "." + to_string(beg.column + 1) + "+" +
-                     to_string((int)context.buffer().distance(beg, sel.max())+1); }
+              return format("{}.{}+{}", beg.line + 1, beg.column + 1,
+                            context.buffer().distance(beg, sel.max())+1); }
         }, {
             "selections_desc",
             [](StringView name, const Context& context)
             { return join(transformed(context.selections(), [&](const Selection& sel) {
                     auto beg = sel.min();
-                    return to_string(beg.line + 1) + "." + to_string(beg.column + 1) + "+" +
-                           to_string((int)context.buffer().distance(beg, sel.max())+1);
+                    return format("{}.{}+{}", beg.line + 1, beg.column + 1,
+                                  context.buffer().distance(beg, sel.max())+1);
                 }), ':'); }
         }, {
             "window_width",
@@ -623,12 +623,12 @@ int main(int argc, char* argv[])
     }
     catch (Kakoune::exception& error)
     {
-        on_assert_failed(("uncaught exception ("_str + typeid(error).name() + "):\n" + error.what()).c_str());
+        on_assert_failed(format("uncaught exception ({}):\n{}", typeid(error).name(), error.what()).c_str());
         return -1;
     }
     catch (std::exception& error)
     {
-        on_assert_failed(("uncaught exception ("_str + typeid(error).name() + "):\n" + error.what()).c_str());
+        on_assert_failed(format("uncaught exception ({}):\n{}", typeid(error).name(), error.what()).c_str());
         return -1;
     }
     catch (...)
diff --git a/src/normal.cc b/src/normal.cc
index 3ba7760a..e4d22cc6 100644
--- a/src/normal.cc
+++ b/src/normal.cc
@@ -470,8 +470,8 @@ void select_next_match(const Buffer& buffer, SelectionList& selections,
 void yank(Context& context, NormalParams params)
 {
     RegisterManager::instance()[params.reg] = context.selections_content();
-    context.print_status({ "yanked " + to_string(context.selections().size()) +
-                           " selections to register " + StringView{params.reg},
+    context.print_status({ format("yanked {} selections to register {}",
+                                  context.selections().size(), params.reg),
                            get_face("Information") });
 }
 
@@ -1106,8 +1106,8 @@ void jump(Context& context, NormalParams)
 void save_selections(Context& context, NormalParams)
 {
     context.push_jump();
-    context.print_status({ "saved " + to_string(context.selections().size()) +
-                           " selections", get_face("Information") });
+    context.print_status({ format("saved {} selections", context.selections().size()),
+                           get_face("Information") });
 }
 
 void align(Context& context, NormalParams)
diff --git a/src/shared_string.cc b/src/shared_string.cc
index a02dfcda..1d0cb5a9 100644
--- a/src/shared_string.cc
+++ b/src/shared_string.cc
@@ -37,8 +37,8 @@ void StringRegistry::debug_stats() const
         total_refcount += st.second->refcount - 1;
         total_size += (int)st.second->length;
     }
-    write_debug("  data size: " + to_string(total_size) + ", mean: " + to_string((float)total_size/count));
-    write_debug("  refcounts: " + to_string(total_refcount) + ", mean: " + to_string((float)total_refcount/count));
+    write_debug(format("  data size: {}, mean: {}", total_size, (float)total_size/count));
+    write_debug(format("  refcounts: {}, mean: {}", total_refcount, (float)total_refcount/count));
 }
 
 }