diff --git a/src/lib_json/json_reader.cpp b/src/lib_json/json_reader.cpp
index 4eb2d11..da8e83b 100644
--- a/src/lib_json/json_reader.cpp
+++ b/src/lib_json/json_reader.cpp
@@ -1,5 +1,6 @@
 #include <json/reader.h>
 #include <json/value.h>
+#include "json_tool.h"
 #include <utility>
 #include <cstdio>
 #include <cassert>
@@ -66,42 +67,6 @@ containsNewLine( Reader::Location begin,
    return false;
 }
 
-static std::string codePointToUTF8(unsigned int cp)
-{
-   std::string result;
-   
-   // based on description from http://en.wikipedia.org/wiki/UTF-8
-
-   if (cp <= 0x7f) 
-   {
-      result.resize(1);
-      result[0] = static_cast<char>(cp);
-   } 
-   else if (cp <= 0x7FF) 
-   {
-      result.resize(2);
-      result[1] = static_cast<char>(0x80 | (0x3f & cp));
-      result[0] = static_cast<char>(0xC0 | (0x1f & (cp >> 6)));
-   } 
-   else if (cp <= 0xFFFF) 
-   {
-      result.resize(3);
-      result[2] = static_cast<char>(0x80 | (0x3f & cp));
-      result[1] = 0x80 | static_cast<char>((0x3f & (cp >> 6)));
-      result[0] = 0xE0 | static_cast<char>((0xf & (cp >> 12)));
-   }
-   else if (cp <= 0x10FFFF) 
-   {
-      result.resize(4);
-      result[3] = static_cast<char>(0x80 | (0x3f & cp));
-      result[2] = static_cast<char>(0x80 | (0x3f & (cp >> 6)));
-      result[1] = static_cast<char>(0x80 | (0x3f & (cp >> 12)));
-      result[0] = static_cast<char>(0xF0 | (0x7 & (cp >> 18)));
-   }
-
-   return result;
-}
-
 
 // Class Reader
 // //////////////////////////////////////////////////////////////////
diff --git a/src/lib_json/json_tool.h b/src/lib_json/json_tool.h
new file mode 100644
index 0000000..ca4ea4f
--- /dev/null
+++ b/src/lib_json/json_tool.h
@@ -0,0 +1,78 @@
+#ifndef LIB_JSONCPP_JSON_TOOL_H_INCLUDED
+# define LIB_JSONCPP_JSON_TOOL_H_INCLUDED
+
+/* This header provides common string manipulation support, such as UTF-8,
+ * portable conversion from/to string...
+ *
+ * It is an internal header that must not be exposed.
+ */
+
+namespace Json {
+
+/// Converts a unicode code-point to UTF-8.
+static inline std::string 
+codePointToUTF8(unsigned int cp)
+{
+   std::string result;
+   
+   // based on description from http://en.wikipedia.org/wiki/UTF-8
+
+   if (cp <= 0x7f) 
+   {
+      result.resize(1);
+      result[0] = static_cast<char>(cp);
+   } 
+   else if (cp <= 0x7FF) 
+   {
+      result.resize(2);
+      result[1] = static_cast<char>(0x80 | (0x3f & cp));
+      result[0] = static_cast<char>(0xC0 | (0x1f & (cp >> 6)));
+   } 
+   else if (cp <= 0xFFFF) 
+   {
+      result.resize(3);
+      result[2] = static_cast<char>(0x80 | (0x3f & cp));
+      result[1] = 0x80 | static_cast<char>((0x3f & (cp >> 6)));
+      result[0] = 0xE0 | static_cast<char>((0xf & (cp >> 12)));
+   }
+   else if (cp <= 0x10FFFF) 
+   {
+      result.resize(4);
+      result[3] = static_cast<char>(0x80 | (0x3f & cp));
+      result[2] = static_cast<char>(0x80 | (0x3f & (cp >> 6)));
+      result[1] = static_cast<char>(0x80 | (0x3f & (cp >> 12)));
+      result[0] = static_cast<char>(0xF0 | (0x7 & (cp >> 18)));
+   }
+
+   return result;
+}
+
+
+/// Returns true if ch is a control character (in range [0,32[).
+static inline bool 
+isControlCharacter(char ch)
+{
+   return ch > 0 && ch <= 0x1F;
+}
+
+
+/** Converts an unsigned integer to string.
+ * @param value Unsigned interger to convert to string
+ * @param current Input/Output string buffer. Must have at least 10 chars free.
+ */
+static inline void 
+uintToString( unsigned int value, 
+              char *&current )
+{
+   *--current = 0;
+   do
+   {
+      *--current = (value % 10) + '0';
+      value /= 10;
+   }
+   while ( value != 0 );
+}
+
+} // namespace Json {
+
+#endif // LIB_JSONCPP_JSON_TOOL_H_INCLUDED
diff --git a/src/lib_json/json_writer.cpp b/src/lib_json/json_writer.cpp
index cdf4188..3b926e6 100644
--- a/src/lib_json/json_writer.cpp
+++ b/src/lib_json/json_writer.cpp
@@ -1,4 +1,5 @@
 #include <json/writer.h>
+#include "json_tool.h"
 #include <utility>
 #include <assert.h>
 #include <stdio.h>
@@ -13,11 +14,6 @@
 
 namespace Json {
 
-static bool isControlCharacter(char ch)
-{
-   return ch > 0 && ch <= 0x1F;
-}
-
 static bool containsControlCharacter( const char* str )
 {
    while ( *str ) 
@@ -27,17 +23,6 @@ static bool containsControlCharacter( const char* str )
    }
    return false;
 }
-static void uintToString( unsigned int value, 
-                          char *&current )
-{
-   *--current = 0;
-   do
-   {
-      *--current = (value % 10) + '0';
-      value /= 10;
-   }
-   while ( value != 0 );
-}
 
 std::string valueToString( Int value )
 {
@@ -116,7 +101,7 @@ std::string valueToQuotedString( const char *value )
    // We have to walk value and escape any special characters.
    // Appending to std::string is not efficient, but this should be rare.
    // (Note: forward slashes are *not* rare, but I am not escaping them.)
-   unsigned maxsize = strlen(value)*2 + 3; // allescaped+quotes+NULL
+   std::string::size_type maxsize = strlen(value)*2 + 3; // allescaped+quotes+NULL
    std::string result;
    result.reserve(maxsize); // to avoid lots of mallocs
    result += "\"";