diff --git a/Packages/UniGLTF/Runtime/UniJSON/Json/JsonParser.cs b/Packages/UniGLTF/Runtime/UniJSON/Json/JsonParser.cs
index 21a2c2e73..60dc2ad9c 100644
--- a/Packages/UniGLTF/Runtime/UniJSON/Json/JsonParser.cs
+++ b/Packages/UniGLTF/Runtime/UniJSON/Json/JsonParser.cs
@@ -66,14 +66,16 @@ namespace UniJSON
         /// <returns></returns>
         static JsonNode ParsePrimitive(JsonNode tree, Utf8String segment, ValueNodeType valueType)
         {
+            var span = segment.Bytes.Span;
             int i = 1;
-            for (; i < segment.ByteLength; ++i)
+            for (; i < span.Length; ++i)
             {
-                if (Char.IsWhiteSpace((char)segment[i])
-                    || segment[i] == '}'
-                    || segment[i] == ']'
-                    || segment[i] == ','
-                    || segment[i] == ':'
+                var b = span[i];
+                if (Char.IsWhiteSpace((char)b)
+                    || b == '}'
+                    || b == ']'
+                    || b == ','
+                    || b == ':'
                     )
                 {
                     break;
diff --git a/Packages/UniGLTF/Runtime/UniJSON/Utf8String/Utf8Iterator.cs b/Packages/UniGLTF/Runtime/UniJSON/Utf8String/Utf8Iterator.cs
index 9dbc22bb8..686475401 100644
--- a/Packages/UniGLTF/Runtime/UniJSON/Utf8String/Utf8Iterator.cs
+++ b/Packages/UniGLTF/Runtime/UniJSON/Utf8String/Utf8Iterator.cs
@@ -1,19 +1,22 @@
 using System;
-using System.Collections;
-using System.Collections.Generic;
 
 
 namespace UniJSON
 {
-    public struct Utf8Iterator : IEnumerator<Byte>
+    public ref struct Utf8Iterator
     {
-        ReadOnlyMemory<byte> m_memory;
+        ReadOnlySpan<byte> m_span;
         int m_start;
         int m_position;
 
         public Utf8Iterator(ReadOnlyMemory<Byte> memory, int start = 0)
+            : this(memory.Span, start)
         {
-            m_memory = memory;
+        }
+
+        public Utf8Iterator(ReadOnlySpan<Byte> span, int start = 0)
+        {
+            m_span = span;
             m_start = start;
             m_position = -1;
         }
@@ -53,27 +56,22 @@ namespace UniJSON
 
         public byte Current
         {
-            get { return m_memory.Span[m_position]; }
-        }
-
-        object IEnumerator.Current
-        {
-            get { return Current; }
+            get { return m_span[m_position]; }
         }
 
         public byte Second
         {
-            get { return m_memory.Span[m_position + 1]; }
+            get { return m_span[m_position + 1]; }
         }
 
         public byte Third
         {
-            get { return m_memory.Span[m_position + 2]; }
+            get { return m_span[m_position + 2]; }
         }
 
         public byte Fourth
         {
-            get { return m_memory.Span[m_position + 3]; }
+            get { return m_span[m_position + 3]; }
         }
 
         public const uint Mask1 = 0x01;
@@ -170,10 +168,6 @@ namespace UniJSON
             }
         }
 
-        public void Dispose()
-        {
-        }
-
         public bool MoveNext()
         {
             if (m_position == -1)
@@ -184,7 +178,7 @@ namespace UniJSON
             {
                 m_position += CurrentByteLength;
             }
-            return m_position < m_memory.Length;
+            return m_position < m_span.Length;
         }
 
         public void Reset()
diff --git a/Packages/UniGLTF/Runtime/UniJSON/Utf8String/Utf8String.cs b/Packages/UniGLTF/Runtime/UniJSON/Utf8String/Utf8String.cs
index 9a6a70802..fdf9f179e 100644
--- a/Packages/UniGLTF/Runtime/UniJSON/Utf8String/Utf8String.cs
+++ b/Packages/UniGLTF/Runtime/UniJSON/Utf8String/Utf8String.cs
@@ -139,38 +139,12 @@ namespace UniJSON
 
         public bool StartsWith(Utf8String rhs)
         {
-            if (rhs.ByteLength > ByteLength)
-            {
-                return false;
-            }
-
-            for (int i = 0; i < rhs.ByteLength; ++i)
-            {
-                if (this[i] != rhs[i])
-                {
-                    return false;
-                }
-            }
-
-            return true;
+            return Bytes.Span.StartsWith(rhs.Bytes.Span);
         }
 
         public bool EndsWith(Utf8String rhs)
         {
-            if (rhs.ByteLength > ByteLength)
-            {
-                return false;
-            }
-
-            for (int i = 1; i <= rhs.ByteLength; ++i)
-            {
-                if (this[ByteLength - i] != rhs[rhs.ByteLength - i])
-                {
-                    return false;
-                }
-            }
-
-            return true;
+            return Bytes.Span.EndsWith(rhs.Bytes.Span);
         }
 
         public int IndexOf(Byte code)
@@ -219,10 +193,11 @@ namespace UniJSON
 
         public Utf8String TrimStart()
         {
+            var span = Bytes.Span;
             var i = 0;
-            for (; i < ByteLength; ++i)
+            for (; i < span.Length; ++i)
             {
-                if (!IsSpace(this[i]))
+                if (!IsSpace(span[i]))
                 {
                     break;
                 }
@@ -232,10 +207,11 @@ namespace UniJSON
 
         public Utf8String TrimEnd()
         {
-            var i = ByteLength-1;
+            var span = Bytes.Span;
+            var i = span.Length - 1;
             for (; i >= 0; --i)
             {
-                if (!IsSpace(this[i]))
+                if (!IsSpace(span[i]))
                 {
                     break;
                 }
@@ -265,20 +241,7 @@ namespace UniJSON
 
         public bool Equals(Utf8String other)
         {
-            if (ByteLength != other.ByteLength)
-            {
-                return false;
-            }
-
-            for (int i = 0; i < ByteLength; ++i)
-            {
-                if (this[i] != other[i])
-                {
-                    return false;
-                }
-            }
-
-            return true;
+            return Bytes.Span.SequenceEqual(other.Bytes.Span);
         }
 
         public override int GetHashCode()
@@ -296,9 +259,10 @@ namespace UniJSON
             get
             {
                 //bool isInt = false;
-                for (int i = 0; i < ByteLength; ++i)
+                var span = Bytes.Span;
+                for (int i = 0; i < span.Length; ++i)
                 {
-                    var c = this[i];
+                    var c = span[i];
                     if (c == '0'
                         || c == '1'
                         || c == '2'
diff --git a/Packages/UniGLTF/Runtime/UniJSON/Utf8String/Utf8StringExtensions.cs b/Packages/UniGLTF/Runtime/UniJSON/Utf8String/Utf8StringExtensions.cs
index c9530bd1c..f2b7cab4e 100644
--- a/Packages/UniGLTF/Runtime/UniJSON/Utf8String/Utf8StringExtensions.cs
+++ b/Packages/UniGLTF/Runtime/UniJSON/Utf8String/Utf8StringExtensions.cs
@@ -23,10 +23,11 @@ namespace UniJSON
 
         public static bool TrySearchByte(this Utf8String src, Func<byte, bool> pred, out int pos)
         {
+            var span = src.Bytes.Span;
             pos = 0;
-            for (; pos < src.ByteLength; ++pos)
+            for (; pos < span.Length; ++pos)
             {
-                if (pred(src[pos]))
+                if (pred(span[pos]))
                 {
                     return true;
                 }
@@ -88,6 +89,7 @@ namespace UniJSON
 
         public static IEnumerable<Utf8String> Split(this Utf8String src, byte delimiter)
         {
+            var results = new List<Utf8String>();
             var start = 0;
             var p = new Utf8Iterator(src.Bytes);
             while (p.MoveNext())
@@ -96,11 +98,11 @@ namespace UniJSON
                 {
                     if (p.BytePosition - start == 0)
                     {
-                        yield return default(Utf8String);
+                        results.Add(default(Utf8String));
                     }
                     else
                     {
-                        yield return src.Subbytes(start, p.BytePosition - start);
+                        results.Add(src.Subbytes(start, p.BytePosition - start));
                     }
                     start = p.BytePosition + 1;
                 }
@@ -108,8 +110,9 @@ namespace UniJSON
 
             if (start < p.BytePosition)
             {
-                yield return src.Subbytes(start, p.BytePosition - start);
+                results.Add(src.Subbytes(start, p.BytePosition - start));
             }
+            return results;
         }
 
         #region atoi