diff --git a/LLama/Grammar/GrammarParser.cs b/LLama/Grammar/GrammarParser.cs
new file mode 100644
index 00000000..fca6e4f3
--- /dev/null
+++ b/LLama/Grammar/GrammarParser.cs
@@ -0,0 +1,328 @@
+using LLama.Native;
+using System;
+using System.Collections.Generic;
+
+namespace LLama.Grammar
+{
+    /// <summary>
+    /// Source:
+    /// https://github.com/ggerganov/llama.cpp/blob/6381d4e110bd0ec02843a60bbeb8b6fc37a9ace9/common/grammar-parser.cpp
+    /// 
+    /// The commit hash from URL is the actual commit hash that reflects current C# code.
+    /// </summary>
+    internal class GrammarParser
+    {
+        // NOTE: assumes valid utf8 (but checks for overrun)
+        // copied from llama.cpp
+        public Tuple<uint, ReadOnlyMemory<char>> DecodeUTF8(ReadOnlyMemory<char> src)
+        {
+            ReadOnlySpan<char> span = src.Span;
+            int[] lookup = { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 3, 4 };
+
+            byte firstByte = (byte)span[0];
+            byte highbits = (byte)(firstByte >> 4);
+            int len = lookup[highbits];
+            byte mask = (byte)((1 << (8 - len)) - 1);
+            uint value = (uint)(firstByte & mask);
+
+            int end = len;
+            int pos = 1;
+
+            for (; pos < end && pos < src.Length; pos++)
+            {
+                value = (uint)((value << 6) + ((byte)span[pos] & 0x3F));
+            }
+
+            ReadOnlyMemory<char> nextSpan = src.Slice(pos);
+
+            return new Tuple<uint, ReadOnlyMemory<char>>(value, nextSpan);
+        }
+
+        public uint GetSymbolId(ParseState state, ReadOnlySpan<char> src, int len)
+        {
+            uint nextId = (uint)state.SymbolIds.Count;
+            string key = src.Slice(0, len).ToString();
+
+            if (state.SymbolIds.TryGetValue(key, out uint existingId))
+            {
+                return existingId;
+            }
+            else
+            {
+                state.SymbolIds[key] = nextId;
+                return nextId;
+            }
+        }
+
+        public uint GenerateSymbolId(ParseState state, string baseName)
+        {
+            uint nextId = (uint)state.SymbolIds.Count;
+            string key = $"{baseName}_{nextId}";
+            state.SymbolIds[key] = nextId;
+            return nextId;
+        }
+
+        public void AddRule(ParseState state, uint ruleId, List<LLamaGrammarElement> rule)
+        {
+            while (state.Rules.Count <= ruleId)
+            {
+                state.Rules.Add(new List<LLamaGrammarElement>());
+            }
+
+            state.Rules[(int)ruleId] = rule;
+        }
+
+        public bool IsWordChar(char c)
+        {
+            return ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || c == '-' || ('0' <= c && c <= '9');
+        }
+
+        public Tuple<uint, ReadOnlyMemory<char>> ParseHex(ReadOnlyMemory<char> src, int size)
+        {
+            int pos = 0;
+            int end = size;
+            uint value = 0;
+
+            ReadOnlySpan<char> srcSpan = src.Span;
+
+            for (; pos < end && pos < src.Length; pos++)
+            {
+                value <<= 4;
+                char c = srcSpan[pos];
+                if ('a' <= c && c <= 'f')
+                {
+                    value += (uint)(c - 'a' + 10);
+                }
+                else if ('A' <= c && c <= 'F')
+                {
+                    value += (uint)(c - 'A' + 10);
+                }
+                else if ('0' <= c && c <= '9')
+                {
+                    value += (uint)(c - '0');
+                }
+                else
+                {
+                    break;
+                }
+            }
+
+            if (pos != end)
+            {
+                throw new InvalidOperationException($"Expecting {size} hex chars at {src.ToString()}");
+            }
+
+            return new Tuple<uint, ReadOnlyMemory<char>>(value, src.Slice(pos));
+        }
+
+        public ReadOnlySpan<char> ParseSpace(ReadOnlySpan<char> src, bool newlineOk)
+        {
+            int pos = 0;
+            while (pos < src.Length &&
+                   (src[pos] == ' ' || src[pos] == '\t' || src[pos] == '#' ||
+                    (newlineOk && (src[pos] == '\r' || src[pos] == '\n'))))
+            {
+                if (src[pos] == '#')
+                {
+                    while (pos < src.Length && src[pos] != '\r' && src[pos] != '\n')
+                    {
+                        pos++;
+                    }
+                }
+                else
+                {
+                    pos++;
+                }
+            }
+            return src.Slice(pos);
+        }
+
+        public ReadOnlySpan<char> ParseName(ReadOnlySpan<char> src)
+        {
+            int pos = 0;
+            while (pos < src.Length && IsWordChar(src[pos]))
+            {
+                pos++;
+            }
+            if (pos == 0)
+            {
+                throw new InvalidOperationException($"Expecting name at {src.ToString()}");
+            }
+            return src.Slice(pos);
+        }
+
+        public Tuple<uint, ReadOnlyMemory<char>> ParseChar(ReadOnlyMemory<char> src)
+        {
+            ReadOnlySpan<char> span = src.Span;
+
+            if (span[0] == '\\')
+            {
+                switch (span[1])
+                {
+                    case 'x':
+                        return ParseHex(src.Slice(2), 2);
+                    case 'u':
+                        return ParseHex(src.Slice(2), 4);
+                    case 'U':
+                        return ParseHex(src.Slice(2), 8);
+                    case 't':
+                        return new Tuple<uint, ReadOnlyMemory<char>>('\t', src.Slice(2));
+                    case 'r':
+                        return new Tuple<uint, ReadOnlyMemory<char>>('\r', src.Slice(2));
+                    case 'n':
+                        return new Tuple<uint, ReadOnlyMemory<char>>('\n', src.Slice(2));
+                    case '\\':
+                    case '"':
+                    case '[':
+                    case ']':
+                        return new Tuple<uint, ReadOnlyMemory<char>>(span[1], src.Slice(2));
+                    default:
+                        throw new Exception("Unknown escape at " + src.ToString());
+                }
+            }
+            else if (!span.IsEmpty)
+            {
+                return DecodeUTF8(src);
+            }
+
+            throw new Exception("Unexpected end of input");
+        }
+
+        public ReadOnlySpan<char> ParseSequence(
+            ref ParseState state,
+            ReadOnlyMemory<char> src,
+            string ruleName,
+            List<LLamaGrammarElement> outElements,
+            bool isNested)
+        {
+            int lastSymStart = outElements.Count;
+            var pos = src.Span;
+
+            while (!pos.IsEmpty)
+            {
+                if (pos[0] == '"')  // literal string
+                {
+                    pos = pos.Slice(1);
+                    lastSymStart = outElements.Count;
+
+                    while (pos[0] != '"')
+                    {
+                        var charPair = ParseChar(src);
+                        pos = charPair.Item2.Span;
+                        outElements.Add(new LLamaGrammarElement { Type = LLamaGrammarElementType.CHAR, Value = charPair.Item1 });
+                    }
+                    pos = ParseSpace(pos.Slice(1), isNested);
+                }
+                else if (pos[0] == '[')  // char range(s)
+                {
+                    pos = pos.Slice(1);
+                    var startType = LLamaGrammarElementType.CHAR;
+
+                    if (pos[0] == '^')
+                    {
+                        pos = pos.Slice(1);
+                        startType = LLamaGrammarElementType.CHAR_NOT;
+                    }
+
+                    lastSymStart = outElements.Count;
+
+                    while (pos[0] != ']')
+                    {
+                        var charPair = ParseChar(src);
+                        pos = charPair.Item2.Span;
+                        var type = lastSymStart < outElements.Count ? LLamaGrammarElementType.CHAR_ALT : startType;
+
+                        outElements.Add(new LLamaGrammarElement { Type = type, Value = charPair.Item1 });
+
+                        if (pos[0] == '-' && pos[1] != ']')
+                        {
+                            var endCharPair = ParseChar(src.Slice(1));
+                            pos = endCharPair.Item2.Span;
+                            outElements.Add(new LLamaGrammarElement { Type = LLamaGrammarElementType.CHAR_RNG_UPPER, Value = endCharPair.Item1 });
+                        }
+                    }
+                    pos = ParseSpace(pos.Slice(1), isNested);
+                }
+                else if (IsWordChar(pos[0]))  // rule reference
+                {
+                    var nameEnd = ParseName(pos);
+                    uint refRuleId = GetSymbolId(state, pos, nameEnd.Length);
+                    pos = ParseSpace(nameEnd, isNested);
+                    lastSymStart = outElements.Count;
+                    outElements.Add(new LLamaGrammarElement { Type = LLamaGrammarElementType.RULE_REF, Value = refRuleId });
+                }
+                else if (pos[0] == '(')  // grouping
+                {
+                    // parse nested alternates into synthesized rule
+                    pos = ParseSpace(pos.Slice(1), true);
+                    uint subRuleId = GenerateSymbolId(state, ruleName);
+                    pos = ParseAlternates(state, pos, ruleName, subRuleId, true);
+                    lastSymStart = outElements.Count;
+                    // output reference to synthesized rule
+                    outElements.Add(new LLamaGrammarElement { Type = LLamaGrammarElementType.RULE_REF, Value = subRuleId });
+                    if (pos[0] != ')')
+                    {
+                        throw new Exception($"Expecting ')' at {new string(pos.ToArray())}");
+                    }
+                    pos = ParseSpace(pos.Slice(1), isNested);
+                }
+                else if (pos[0] == '*' || pos[0] == '+' || pos[0] == '?') // repetition operator
+                {
+                    if (lastSymStart == outElements.Count)
+                    {
+                        throw new Exception($"Expecting preceding item to */+/? at {new string(pos.ToArray())}");
+                    }
+
+                    // apply transformation to previous symbol (lastSymStart to end) according to
+                    // rewrite rules:
+                    // S* --> S' ::= S S' |
+                    // S+ --> S' ::= S S' | S
+                    // S? --> S' ::= S |
+                    uint subRuleId = GenerateSymbolId(state, ruleName);
+
+                    List<LLamaGrammarElement> subRule = new List<LLamaGrammarElement>();
+
+                    // add preceding symbol to generated rule
+                    subRule.AddRange(outElements.GetRange(lastSymStart, outElements.Count - lastSymStart));
+
+                    if (pos[0] == '*' || pos[0] == '+')
+                    {
+                        // cause generated rule to recurse
+                        subRule.Add(new LLamaGrammarElement { Type = LLamaGrammarElementType.RULE_REF, Value = subRuleId });
+                    }
+
+                    // mark start of alternate def
+                    subRule.Add(new LLamaGrammarElement { Type = LLamaGrammarElementType.ALT, Value = 0 });
+
+                    if (pos[0] == '+')
+                    {
+                        // add preceding symbol as alternate only for '+' (otherwise empty)
+                        subRule.AddRange(outElements.GetRange(lastSymStart, outElements.Count - lastSymStart));
+                    }
+
+                    subRule.Add(new LLamaGrammarElement { Type = LLamaGrammarElementType.END, Value = 0 });
+
+                    AddRule(state, subRuleId, subRule);
+
+                    // in original rule, replace previous symbol with reference to generated rule
+                    outElements.RemoveRange(lastSymStart, outElements.Count - lastSymStart);
+                    outElements.Add(new LLamaGrammarElement { Type = LLamaGrammarElementType.RULE_REF, Value = subRuleId });
+
+                    pos = ParseSpace(pos.Slice(1), isNested);
+
+                }
+                else
+                {
+                    break;
+                }
+            }
+
+            return pos;
+        }
+
+        public ReadOnlySpan<char> ParseAlternates(ParseState state, ReadOnlySpan<char> pos, string ruleName, uint subRuleId, bool v)
+        {
+            throw new NotImplementedException();
+        }
+    }
+}
diff --git a/LLama/Grammar/ParseState.cs b/LLama/Grammar/ParseState.cs
new file mode 100644
index 00000000..bd5eaf41
--- /dev/null
+++ b/LLama/Grammar/ParseState.cs
@@ -0,0 +1,26 @@
+using LLama.Native;
+using System;
+using System.Collections.Generic;
+
+namespace LLama.Grammar
+{
+    /// <summary>
+    /// Source:
+    /// https://github.com/ggerganov/llama.cpp/blob/6381d4e110bd0ec02843a60bbeb8b6fc37a9ace9/common/grammar-parser.h
+    /// 
+    /// The commit hash from URL is the actual commit hash that reflects current C# code.
+    /// </summary>
+    internal class ParseState
+    {
+        public Dictionary<string, uint> SymbolIds { get; } = new Dictionary<string, uint>();
+        public List<List<LLamaGrammarElement>> Rules { get; } = new List<List<LLamaGrammarElement>>();
+
+        public IEnumerable<List<LLamaGrammarElement>> CRules()
+        {
+            foreach (var rule in Rules)
+            {
+                yield return rule;
+            }
+        }
+    }
+}