diff --git a/src/saveload/saveload.cpp b/src/saveload/saveload.cpp
index 6b0d349f6b..5b743ba20d 100644
--- a/src/saveload/saveload.cpp
+++ b/src/saveload/saveload.cpp
@@ -29,6 +29,7 @@
 #include "../window_func.h"
 #include "../strings_func.h"
 #include "../core/endian_func.hpp"
+#include "../core/string_builder.hpp"
 #include "../vehicle_base.h"
 #include "../company_func.h"
 #include "../timer/timer_game_economy.h"
@@ -928,7 +929,7 @@ void FixSCCEncoded(std::string &str, bool fix_code)
 	 * `:"<STRING>"`              becomes `<RS><SCC_ENCODED_STRING><STRING>`
 	 */
 	std::string result;
-	auto output = std::back_inserter(result);
+	StringBuilder builder(result);
 
 	bool is_encoded = false; // Set if we determine by the presence of SCC_ENCODED that the string is an encoded string.
 	bool in_string = false; // Set if we in a string, between double-quotes.
@@ -940,11 +941,11 @@ void FixSCCEncoded(std::string &str, bool fix_code)
 
 		char32_t c;
 		Utf8Decode(&c, &*it);
+		it += len;
 		if (c == SCC_ENCODED || (fix_code && (c == 0xE028 || c == 0xE02A))) {
-			Utf8Encode(output, SCC_ENCODED);
+			builder.PutUtf8(SCC_ENCODED);
 			need_type = false;
 			is_encoded = true;
-			it += len;
 			continue;
 		}
 
@@ -955,27 +956,24 @@ void FixSCCEncoded(std::string &str, bool fix_code)
 			in_string = !in_string;
 			if (in_string && need_type) {
 				/* Started a new string parameter. */
-				Utf8Encode(output, SCC_ENCODED_STRING);
+				builder.PutUtf8(SCC_ENCODED_STRING);
 				need_type = false;
 			}
-			it += len;
 			continue;
 		}
 
 		if (!in_string && c == ':') {
-			*output = SCC_RECORD_SEPARATOR;
+			builder.PutUtf8(SCC_RECORD_SEPARATOR);
 			need_type = true;
-			it += len;
 			continue;
 		}
 		if (need_type) {
 			/* Started a new numeric parameter. */
-			Utf8Encode(output, SCC_ENCODED_NUMERIC);
+			builder.PutUtf8(SCC_ENCODED_NUMERIC);
 			need_type = false;
 		}
 
-		Utf8Encode(output, c);
-		it += len;
+		builder.PutUtf8(c);
 	}
 
 	str = std::move(result);
diff --git a/src/script/api/script_text.cpp b/src/script/api/script_text.cpp
index 5cc784a427..89333e6982 100644
--- a/src/script/api/script_text.cpp
+++ b/src/script/api/script_text.cpp
@@ -163,9 +163,9 @@ EncodedString ScriptText::GetEncodedText()
 	ParamList params;
 	int param_count = 0;
 	std::string result;
-	auto output = std::back_inserter(result);
+	StringBuilder builder(result);
 	this->_FillParamList(params, seen_texts);
-	this->_GetEncodedText(output, param_count, params, true);
+	this->_GetEncodedText(builder, param_count, params, true);
 	if (param_count > SCRIPT_TEXT_MAX_PARAMETERS) throw Script_FatalError(fmt::format("{}: Too many parameters", GetGameStringName(this->string)));
 	return ::EncodedString{std::move(result)};
 }
@@ -193,46 +193,46 @@ void ScriptText::_FillParamList(ParamList &params, ScriptTextList &seen_texts)
 	}
 }
 
-void ScriptText::ParamCheck::Encode(std::back_insert_iterator<std::string> &output, std::string_view cmd)
+void ScriptText::ParamCheck::Encode(StringBuilder &builder, std::string_view cmd)
 {
 	if (this->cmd.empty()) this->cmd = cmd;
 	if (this->used) return;
 
 	struct visitor {
-		std::back_insert_iterator<std::string> &output;
+		StringBuilder &builder;
 
 		void operator()(std::string value)
 		{
-			Utf8Encode(this->output, SCC_ENCODED_STRING);
+			this->builder.PutUtf8(SCC_ENCODED_STRING);
 			StrMakeValidInPlace(value, {StringValidationSetting::ReplaceWithQuestionMark, StringValidationSetting::AllowNewline, StringValidationSetting::ReplaceTabCrNlWithSpace});
-			fmt::format_to(this->output, "{}", value);
+			this->builder.Put(value);
 		}
 
 		void operator()(const SQInteger &value)
 		{
-			Utf8Encode(this->output, SCC_ENCODED_NUMERIC);
-			fmt::format_to(this->output, "{:X}", value);
+			this->builder.PutUtf8(SCC_ENCODED_NUMERIC);
+			this->builder.PutIntegerBase(value, 16);
 		}
 
 		void operator()(const ScriptTextRef &value)
 		{
-			Utf8Encode(this->output, SCC_ENCODED);
-			fmt::format_to(this->output, "{:X}", value->string);
+			this->builder.PutUtf8(SCC_ENCODED);
+			this->builder.PutIntegerBase(value->string.base(), 16);
 		}
 	};
 
-	*output = SCC_RECORD_SEPARATOR;
-	std::visit(visitor{output}, *this->param);
+	builder.PutUtf8(SCC_RECORD_SEPARATOR);
+	std::visit(visitor{builder}, *this->param);
 	this->used = true;
 }
 
-void ScriptText::_GetEncodedText(std::back_insert_iterator<std::string> &output, int &param_count, ParamSpan args, bool first)
+void ScriptText::_GetEncodedText(StringBuilder &builder, int &param_count, ParamSpan args, bool first)
 {
 	const std::string &name = GetGameStringName(this->string);
 
 	if (first) {
-		Utf8Encode(output, SCC_ENCODED);
-		fmt::format_to(output, "{:X}", this->string);
+		builder.PutUtf8(SCC_ENCODED);
+		builder.PutIntegerBase(this->string.base(), 16);
 	}
 
 	const StringParams &params = GetGameStringParams(this->string);
@@ -256,7 +256,7 @@ void ScriptText::_GetEncodedText(std::back_insert_iterator<std::string> &output,
 				case StringParam::RAW_STRING:
 				{
 					ParamCheck &p = *get_next_arg();
-					p.Encode(output, cur_param.cmd);
+					p.Encode(builder, cur_param.cmd);
 					if (p.cmd != cur_param.cmd) throw 1;
 					if (!std::holds_alternative<std::string>(*p.param)) ScriptLog::Error(fmt::format("{}({}): {{{}}} expects a raw string", name, param_count + 1, cur_param.cmd));
 					break;
@@ -265,7 +265,7 @@ void ScriptText::_GetEncodedText(std::back_insert_iterator<std::string> &output,
 				case StringParam::STRING:
 				{
 					ParamCheck &p = *get_next_arg();
-					p.Encode(output, cur_param.cmd);
+					p.Encode(builder, cur_param.cmd);
 					if (p.cmd != cur_param.cmd) throw 1;
 					if (!std::holds_alternative<ScriptTextRef>(*p.param)) {
 						ScriptLog::Error(fmt::format("{}({}): {{{}}} expects a GSText", name, param_count + 1, cur_param.cmd));
@@ -274,12 +274,12 @@ void ScriptText::_GetEncodedText(std::back_insert_iterator<std::string> &output,
 					}
 					int count = 0;
 					ScriptTextRef &ref = std::get<ScriptTextRef>(*p.param);
-					ref->_GetEncodedText(output, count, args.subspan(idx), false);
+					ref->_GetEncodedText(builder, count, args.subspan(idx), false);
 					if (++count != cur_param.consumes) {
 						ScriptLog::Warning(fmt::format("{}({}): {{{}}} expects {} to be consumed, but {} consumes {}", name, param_count + 1, cur_param.cmd, cur_param.consumes - 1, GetGameStringName(ref->string), count - 1));
 						/* Fill missing params if needed. */
 						for (int i = count; i < cur_param.consumes; i++) {
-							Utf8Encode(output, SCC_RECORD_SEPARATOR);
+							builder.PutUtf8(SCC_RECORD_SEPARATOR);
 						}
 					}
 					skip_args(cur_param.consumes - 1);
@@ -289,7 +289,7 @@ void ScriptText::_GetEncodedText(std::back_insert_iterator<std::string> &output,
 				default:
 					for (int i = 0; i < cur_param.consumes; i++) {
 						ParamCheck &p = *get_next_arg();
-						p.Encode(output, i == 0 ? cur_param.cmd : "");
+						p.Encode(builder, i == 0 ? cur_param.cmd : "");
 						if (i == 0 && p.cmd != cur_param.cmd) throw 1;
 						if (!std::holds_alternative<SQInteger>(*p.param)) ScriptLog::Error(fmt::format("{}({}): {{{}}} expects an integer", name, param_count + i + 1, cur_param.cmd));
 					}
diff --git a/src/script/api/script_text.hpp b/src/script/api/script_text.hpp
index c31da8a400..50f4864358 100644
--- a/src/script/api/script_text.hpp
+++ b/src/script/api/script_text.hpp
@@ -12,6 +12,7 @@
 
 #include "script_object.hpp"
 #include "../../strings_func.h"
+#include "../../core/string_builder.hpp"
 
 #include <variant>
 
@@ -141,7 +142,7 @@ private:
 
 		ParamCheck(StringIndexInTab owner, int idx, Param *param) : owner(owner), idx(idx), param(param) {}
 
-		void Encode(std::back_insert_iterator<std::string> &output, std::string_view cmd);
+		void Encode(StringBuilder &output, std::string_view cmd);
 	};
 
 	using ParamList = std::vector<ParamCheck>;
@@ -168,7 +169,7 @@ private:
 	 * @param args The parameters to be consumed.
 	 * @param first Whether it's the first call in the recursion.
 	 */
-	void _GetEncodedText(std::back_insert_iterator<std::string> &output, int &param_count, ParamSpan args, bool first);
+	void _GetEncodedText(StringBuilder &output, int &param_count, ParamSpan args, bool first);
 
 	/**
 	 * Set a parameter, where the value is the first item on the stack.
diff --git a/src/strings.cpp b/src/strings.cpp
index 9f550b374b..f97b13f46e 100644
--- a/src/strings.cpp
+++ b/src/strings.cpp
@@ -103,41 +103,38 @@ EncodedString GetEncodedString(StringID str)
 EncodedString GetEncodedStringWithArgs(StringID str, std::span<const StringParameter> params)
 {
 	std::string result;
-	auto output = std::back_inserter(result);
-	Utf8Encode(output, SCC_ENCODED_INTERNAL);
-	fmt::format_to(output, "{:X}", str);
+	StringBuilder builder(result);
+	builder.PutUtf8(SCC_ENCODED_INTERNAL);
+	builder.PutIntegerBase(str, 16);
 
 	struct visitor {
-		std::back_insert_iterator<std::string> &output;
+		StringBuilder &builder;
 
 		void operator()(const std::monostate &) {}
 
 		void operator()(const uint64_t &arg)
 		{
-			Utf8Encode(output, SCC_ENCODED_NUMERIC);
-			fmt::format_to(this->output, "{:X}", arg);
+			this->builder.PutUtf8(SCC_ENCODED_NUMERIC);
+			this->builder.PutIntegerBase(arg, 16);
 		}
 
 		void operator()(const std::string &value)
 		{
 #ifdef WITH_ASSERT
 			/* Don't allow an encoded string to contain another encoded string. */
-			if (!value.empty()) {
-				char32_t c;
-				const char *p = value.data();
-				if (Utf8Decode(&c, p)) {
-					assert(c != SCC_ENCODED && c != SCC_ENCODED_INTERNAL && c != SCC_RECORD_SEPARATOR);
-				}
+			{
+				auto [len, c] = DecodeUtf8(value);
+				assert(len == 0 || (c != SCC_ENCODED && c != SCC_ENCODED_INTERNAL && c != SCC_RECORD_SEPARATOR));
 			}
 #endif /* WITH_ASSERT */
-			Utf8Encode(output, SCC_ENCODED_STRING);
-			fmt::format_to(this->output, "{}", value);
+			this->builder.PutUtf8(SCC_ENCODED_STRING);
+			this->builder += value;
 		}
 	};
 
-	visitor v{output};
+	visitor v{builder};
 	for (const auto &param : params) {
-		*output = SCC_RECORD_SEPARATOR;
+		builder.PutUtf8(SCC_RECORD_SEPARATOR);
 		std::visit(v, param.data);
 	}