diff --git a/include/raii/rjp_string.hpp b/include/raii/rjp_string.hpp
index 9ae7612..72bec3a 100644
--- a/include/raii/rjp_string.hpp
+++ b/include/raii/rjp_string.hpp
@@ -48,7 +48,7 @@ namespace raii{
 
 		using string_intermediary<detail::rjp_allocator>::string_intermediary;
 		rjp_string(RJP_value* r):
-			string_intermediary<detail::rjp_allocator>(r ? std::exchange(r->string.value, nullptr) : nullptr, r ? r->string.length : 0){}
+			string_intermediary<detail::rjp_allocator>(r ? std::exchange(r->string.value, nullptr) : nullptr, r ? r->string.length : 0, r ? r->string.length : 0){}
 		using string_intermediary<detail::rjp_allocator>::operator=;
 		rjp_string& operator=(RJP_value* r){
 			if(!r)
@@ -56,6 +56,7 @@ namespace raii{
 			reset();
 			m_data = std::exchange(r->string.value, nullptr);
 			m_length = r->string.length;
+			m_cap = r->string.length;
 			return *this;
 		}
 	};
diff --git a/include/raii/string_base.hpp b/include/raii/string_base.hpp
index d6728ef..0373060 100644
--- a/include/raii/string_base.hpp
+++ b/include/raii/string_base.hpp
@@ -32,15 +32,18 @@ namespace raii{
 	{
 	protected:
 		size_t m_length = 0;
+		size_t m_cap = 0;
 		char* m_data = nullptr;
 
 	protected:
 		constexpr string_base(void) = default;
 		constexpr string_base(size_t len):
-			m_length(len){}
+			m_cap(len){}
 		//Initialize without copying
 		constexpr string_base(char* data, size_t len):
-			m_length(len), m_data(data){}
+			m_cap(len), m_data(data){}
+		constexpr string_base(char* data, size_t len, size_t cap):
+			m_length(len), m_cap(cap), m_data(data){}
 		//Copy ctor (do nothing)
 		string_base(const string_base&){}
 		~string_base(void) = default;
@@ -51,6 +54,7 @@ namespace raii{
 
 		//Length of string not including null terminator
 		constexpr size_t length(void)const{return m_length;}
+		constexpr size_t capacity(void)const{return m_cap;}
 		//direct access to managed pointer
 		constexpr char* get(void){return m_data;}
 		constexpr const char* get(void)const{return m_data;}
@@ -75,8 +79,10 @@ namespace raii{
 		string_intermediary(void) = default;
 		string_intermediary(char* data, size_t len);
 		string_intermediary(const char* data, size_t len);
+		string_intermediary(char* data, size_t len, size_t cap);
 		string_intermediary(const char* data);
 		string_intermediary(size_t len);
+		string_intermediary(size_t len, size_t cap);
 
 		//normal copy and move ctors
 		string_intermediary(const string_intermediary& b);
@@ -184,7 +190,6 @@ namespace raii{
 		{
 		private:
 			Targ& m_targ;
-			size_t m_pos = 0;
 		public:
 			appender(Targ& t);
 			template<class L, class R>
diff --git a/include/raii/string_base.tpp b/include/raii/string_base.tpp
index 1279c60..682a471 100644
--- a/include/raii/string_base.tpp
+++ b/include/raii/string_base.tpp
@@ -22,12 +22,16 @@
 #include <utility> //forward, move, swap, etc
 #include <cstdlib> //memcpy
 #include <cstring> //strlen, strcpy
+#include <algorithm> //max
 
 namespace raii{
 	template<class Allocator>
 	string_intermediary<Allocator>::string_intermediary(char* data, size_t len):
 		string_base(data, len){}
 	template<class Allocator>
+	string_intermediary<Allocator>::string_intermediary(char* data, size_t len, size_t cap):
+		string_base(data, len, cap){}
+	template<class Allocator>
 	string_intermediary<Allocator>::string_intermediary(const char* data, size_t len):
 		string_base(reinterpret_cast<char*>(len ? Allocator::copy(data, len+1) : nullptr), len)
 	{
@@ -37,8 +41,10 @@ namespace raii{
 	string_intermediary<Allocator>::string_intermediary(const char* data):
 		string_base(data ? strlen(data) : 0)
 	{
-		if(m_length)
-			m_data = reinterpret_cast<char*>(Allocator::copy(data, m_length+1));
+		if(m_cap){
+			m_data = reinterpret_cast<char*>(Allocator::copy(data, m_cap+1));
+			m_length = m_cap;
+		}
 	}
 	template<class Allocator>
 	string_intermediary<Allocator>::string_intermediary(size_t len):
@@ -46,18 +52,24 @@ namespace raii{
 	{
 		m_data[len] = 0;
 	}
+	template<class Allocator>
+	string_intermediary<Allocator>::string_intermediary(size_t len, size_t cap):
+		string_base(reinterpret_cast<char*>(len ? Allocator::allocate(len+1) : nullptr), len, cap)
+	{
+		m_data[len] = 0;
+	}
 
 	//normal copy and move ctors
 	template<class Allocator>
 	string_intermediary<Allocator>::string_intermediary(const string_intermediary& b):
-		string_base(reinterpret_cast<char*>(b.m_length ? Allocator::copy(b.m_data, b.m_length+1) : nullptr), b.m_length){}
+		string_base(reinterpret_cast<char*>(b.m_length ? Allocator::copy(b.m_data, b.m_length+1) : nullptr), b.m_length, b.m_cap){}
 	template<class Allocator>
 	string_intermediary<Allocator>::string_intermediary(string_intermediary&& s):
-		string_base(std::exchange(s.m_data, nullptr), s.m_length){}
+		string_base(std::exchange(s.m_data, nullptr), s.m_length, s.m_cap){}
 
 	template<class Allocator>
 	string_intermediary<Allocator>::string_intermediary(const string_base& b):
-		string_base(reinterpret_cast<char*>(b.length() ? Allocator::copy(b.get(), b.length()+1) : nullptr), b.length()){}
+		string_base(reinterpret_cast<char*>(b.length() ? Allocator::copy(b.get(), b.length()+1) : nullptr), b.length(), b.capacity()){}
 
 	//dtor
 	template<class Allocator>
@@ -67,6 +79,11 @@ namespace raii{
 
 	template<class Allocator>
 	string_intermediary<Allocator>& string_intermediary<Allocator>::operator=(const string_intermediary& s){
+		if(s.m_length < m_length){
+			memcpy(m_data, s.m_data, s.m_length+1);
+			m_length = s.m_length;
+			return *this;
+		}
 		string_intermediary tmp(s);
 		return (*this = std::move(tmp));
 	}
@@ -74,6 +91,7 @@ namespace raii{
 	string_intermediary<Allocator>& string_intermediary<Allocator>::operator=(string_intermediary&& s){
 		std::swap(m_data, s.m_data);
 		m_length = s.m_length;
+		m_cap = s.m_cap;
 		return *this;
 	}
 	//Copy from c string
@@ -93,16 +111,18 @@ namespace raii{
 		Allocator::free(m_data);
 		m_data = val;
 		m_length = val ? strlen(val) : 0;
+		m_cap = m_length;
 	}
 	template<class Allocator>
 	void string_intermediary<Allocator>::reset(char* val, size_t len){
 		Allocator::free(m_data);
 		m_data = val;
 		m_length = len;
+		m_cap = len;
 	}
 	template<class Allocator>
 	bool string_intermediary<Allocator>::resize(size_t newsize){
-		if(newsize < m_length)
+		if(newsize < m_cap)
 			return false;
 		string_intermediary tmp(newsize);
 		memcpy(tmp.get(), m_data, m_length);
@@ -112,23 +132,27 @@ namespace raii{
 	}
 	template<class Allocator>
 	void string_intermediary<Allocator>::append(const char* data, size_t len){
-		string_intermediary tmp(m_length + len);
-		memcpy(tmp.m_data, m_data, m_length);
-		memcpy(tmp.m_data+m_length, data, len);
-		tmp[m_length+len] = 0;
-		*this = std::move(tmp);
+		if(len+m_length <= m_cap){
+			memcpy(m_data+m_length, data, len);
+			m_length += len;
+			m_data[m_length] = 0;
+		}else{
+			string_intermediary tmp(std::max(m_length + len, m_cap*2));
+			memcpy(tmp.m_data, m_data, m_length);
+			memcpy(tmp.m_data+m_length, data, len);
+			tmp.m_length = len+m_length;
+			tmp[m_length+len] = 0;
+			*this = std::move(tmp);
+		}
 	}
 	template<class Allocator>
 	void string_intermediary<Allocator>::append(const char* data){
-		size_t len = strlen(data);
-		resize(m_length+len);
-		memcpy(m_data+m_length, data, len);
-		m_length += len;
-		m_data[m_length] = 0;
+		if(data)
+			append(data, strlen(data));
 	}
 	template<class Allocator>
 	void string_intermediary<Allocator>::append(const string_base& s){
-		append(s.get());
+		append(s.get(), s.length());
 	}
 
 	template<class Allocator>
@@ -136,15 +160,18 @@ namespace raii{
 		if(!len){
 			Allocator::free(m_data);
 			m_length = 0;
+			m_cap = 0;
 			return *this;
 		}
 		if(len <= m_length){
 			strcpy(m_data, s);
 		}else{
 			Allocator::free(m_data);
-			m_data = reinterpret_cast<char*>(Allocator::copy(s, len+1));
+			m_cap = std::max(len, m_cap*2);
+			m_data = reinterpret_cast<char*>(Allocator::copy(s, m_cap+1));
 			if(!m_data){
 				m_length = 0;
+				m_cap = 0;
 				return *this;
 			}
 		}
@@ -174,9 +201,8 @@ namespace raii{
 	template<class Left, class Right>
 	template<class Alloc>
 	string_cat_expr<Left,Right>::operator string_intermediary<Alloc>(void){
-		string_intermediary<Alloc> ret(length());
-		for(size_t i = 0;i < length();++i)
-			ret[i] = 'n';
+		size_t len = length();
+		string_intermediary<Alloc> ret(len);
 		detail::appender<string_intermediary<Alloc>> append(ret);
 		append(*this);
 		return ret;
@@ -193,13 +219,13 @@ namespace raii{
 
 	template<size_t N>
 	constexpr static_string::static_string(const char(&str)[N]):
-		string_base(const_cast<char*>(str), N){}
+		string_base(const_cast<char*>(str), N, N){}
 	constexpr static_string::static_string(const char* str, size_t len):
-		string_base(const_cast<char*>(str), len){}
+		string_base(const_cast<char*>(str), len, len){}
 	constexpr static_string::static_string(const static_string& s):
-		string_base(s.m_data, s.m_length){}
+		string_base(s.m_data, s.m_length, s.m_length){}
 	constexpr static_string::static_string(static_string&& s):
-		string_base(s.m_data, s.m_length){}
+		string_base(s.m_data, s.m_length, s.m_length){}
 
 	namespace detail{
 		template<class Targ>
@@ -212,8 +238,7 @@ namespace raii{
 		}
 		template<class Targ>
 		void appender<Targ>::operator()(const string_base& str){
-			memcpy(m_targ.get()+m_pos, str.get(), str.length());
-			m_pos += str.length();
+			m_targ.append(str.get(), str.length());
 		}
 	}
 
diff --git a/src/raii/curler.cpp b/src/raii/curler.cpp
index 4868ea2..5144ead 100644
--- a/src/raii/curler.cpp
+++ b/src/raii/curler.cpp
@@ -114,7 +114,8 @@ namespace raii{
 
 	curl_string curler::encode(const char* data, int len){
 		char* tmp = curl_easy_escape(m_curl, data, len);
-		return curl_string(tmp, strlen(tmp));
+		size_t esclen = strlen(tmp);
+		return curl_string(tmp, esclen, esclen);
 	}
 	curl_string curler::decode(const char* data, int* outlen, int len){
 		if(outlen)
diff --git a/src/raii/string_base.cpp b/src/raii/string_base.cpp
index b2f2b63..1ff38a3 100644
--- a/src/raii/string_base.cpp
+++ b/src/raii/string_base.cpp
@@ -34,7 +34,7 @@ namespace raii{
 	}
 
 	static_string::static_string(const char* c):
-		string_base(const_cast<char*>(c), strlen(c)){}
+		static_string(const_cast<char*>(c), strlen(c)){}
 	static_string& static_string::operator=(const char* c){
 		m_data = const_cast<char*>(c);
 		m_length = strlen(c);
diff --git a/src/raii/util.cpp b/src/raii/util.cpp
index 22f7c4e..7c359a2 100644
--- a/src/raii/util.cpp
+++ b/src/raii/util.cpp
@@ -87,7 +87,7 @@ namespace raii{
 		char* tmp = reinterpret_cast<char*>(string::allocator_type::allocate(len+1));
 		detail::_sanitize_json_copy(tmp, str);
 		tmp[len] = 0;
-		return string(tmp, len);
+		return string(tmp, len, len);
 	}
 
 
@@ -116,7 +116,7 @@ namespace raii{
 		if(i == 0)
 			return raii::string("0");
 		int place = intlen(i);
-		raii::string ret(place);
+		raii::string ret(place, place);
 		char* buf = ret.get();
 		buf[place] = 0;
 		while(i != 0){