diff --git a/build.bat b/build.bat
index cbea7d1..ce3ca07 100644
--- a/build.bat
+++ b/build.bat
@@ -16,6 +16,7 @@ echo ~~~ Build All Tests ~~~
 cl %compile_flags% ..\tests\sanity_tests.c
 cl %compile_flags% ..\tests\unicode_test.c
 cl %compile_flags% ..\tests\cpp_build_test.cpp
+cl %compile_flags% ..\tests\grammar.c
 popd
 
 echo.
diff --git a/build.sh b/build.sh
index 1af5ba8..2a100ff 100755
--- a/build.sh
+++ b/build.sh
@@ -28,6 +28,7 @@ echo ~~~ Build All Tests ~~~
 $CC $compile_flags ../tests/sanity_tests.c -o sanity_tests
 $CC $compile_flags ../tests/unicode_test.c -o unicode_test
 clang++ $compile_flags ../tests/cpp_build_test.cpp
+$CC $compile_flags ../tests/grammar.c -o grammar
 popd
 
 echo
diff --git a/tests/grammar.c b/tests/grammar.c
new file mode 100644
index 0000000..6e12ced
--- /dev/null
+++ b/tests/grammar.c
@@ -0,0 +1,476 @@
+#include "md.h"
+#include "md.c"
+#include <stdlib.h>     
+
+// NOTE: https://www.pcg-random.org/download.html
+typedef struct RandomSeries{
+    MD_u64 state; // NOTE: RNG state.  All values are possible.
+    MD_u64 inc;   //       Controls which RNG sequence (stream) is selected. Odd at all times.
+} RandomSeries;
+
+static MD_u32 rand_U32(RandomSeries* rng)
+{
+    MD_u64 oldstate = rng->state;
+    rng->state = oldstate * 6364136223846793005ULL + rng->inc;
+    MD_u32 xorshifted = ((oldstate >> 18u) ^ oldstate) >> 27u;
+    MD_u32 rot = oldstate >> 59u;
+    return (xorshifted >> rot) | (xorshifted << ((-rot) & 31));
+}
+
+static RandomSeries rand_seed(MD_u64 initstate, MD_u64 initseq)
+{
+    RandomSeries result = {0};
+
+    result.state = 0U;
+    result.inc = (initseq << 1u) | 1u;        // NOTE: inc must be odd
+    rand_U32(&result);
+    result.state += initstate;
+    rand_U32(&result);
+
+    return result;
+}
+
+MD_GLOBAL struct
+{
+    RandomSeries *random_series;
+    MD_NodeTable *production_table;
+} globals = {0};
+
+static void TagSquareBracketSetsAsOptional(MD_Node *node, MD_Node *optional_tag)
+{
+    if(node->kind == MD_NodeKind_Label && 
+       (node->flags & MD_NodeFlag_BracketLeft) && (node->flags & MD_NodeFlag_BracketRight))
+    {
+        if(node->string.size) // NOTE(mal): Production. Tag belongs to the first child
+        {
+            MD_Assert(!MD_NodeIsNil(node->first_child));
+            MD_PushTag(node->first_child, optional_tag);
+        }
+        else
+        {
+            MD_PushTag(node, optional_tag);
+        }
+    }
+
+    for(MD_EachNode(child, node->first_child))
+    {
+        TagSquareBracketSetsAsOptional(child, optional_tag);
+    }
+}
+
+static MD_Node * NewChildLabel(MD_Node *parent, MD_String8 label)
+{
+    MD_Node *result = 0;
+
+    result = MD_MakeNodeFromString(MD_NodeKind_Label, MD_S8Lit(""), 0, 0, label);
+    if(parent)
+    {
+        MD_PushChild(parent, result);
+    }
+    return result;
+}
+
+static MD_Node * NewChild(MD_Node *parent)
+{
+    MD_Node *result = NewChildLabel(parent, MD_S8Lit(""));
+    return result;
+}
+
+#define OPTIONAL_TAG "optional"
+
+static void PrintRule(MD_Node *rule)
+{
+    MD_b32 is_literal_char = rule->flags & MD_NodeFlag_CharLiteral;
+
+    MD_b32 optional = MD_NodeHasTag(rule, MD_S8Lit(OPTIONAL_TAG));
+
+    if(optional)
+    {
+        printf("[");
+    }
+
+    for(MD_EachNode(tag, rule->first_tag))
+    {
+        if(!MD_StringMatch(tag->string, MD_S8Lit(OPTIONAL_TAG), 0))
+        {
+            printf("@%.*s ", MD_StringExpand(tag->string));
+        }
+    }
+
+    if(is_literal_char)
+    {
+        printf("'");
+    }
+
+    MD_b32 has_children = !MD_NodeIsNil(rule->first_child);
+    if(has_children)
+    {
+        MD_Assert(rule->string.size == 0);
+
+        for(MD_EachNode(rule_element, rule->first_child))
+        {
+            PrintRule(rule_element);
+
+            if(!MD_NodeIsNil(rule_element->next))
+            {
+                printf(" ");
+            }
+        }
+    }
+    else
+    {
+        MD_Assert(rule->string.size > 0);
+        printf("%.*s", MD_StringExpand(rule->string));
+    }
+
+    if(is_literal_char)
+    {
+        printf("'");
+    }
+
+    if(optional)
+    {
+        printf("]");
+    }
+}
+
+typedef enum AllowedOperationFlags AllowedOperationFlags;
+enum AllowedOperationFlags
+{
+    AllowedOperationFlag_Leaf   = 1<<0,
+    AllowedOperationFlag_Tag    = 1<<1,
+};
+
+static void ExpandProduction(MD_Node *production, MD_String8List *out, MD_Node *cur_node, AllowedOperationFlags allowed);
+
+static void Extend(MD_String8 *s, char c)
+{
+    *s = MD_PushStringF("%.*s%c", MD_StringExpand(*s), c);
+}
+
+static void ExpandRule(MD_Node *rule, MD_String8List *out_strings, MD_Node *cur_node, AllowedOperationFlags allowed)
+{
+    for(MD_EachNode(rule_element, rule->first_child))
+    {
+        MD_b32 expand = 1;
+        if(MD_NodeHasTag(rule_element, MD_S8Lit(OPTIONAL_TAG)))
+        {
+            expand = rand_U32(globals.random_series)%2;
+        }
+
+        if(expand)
+        {
+            MD_b32 has_children = !MD_NodeIsNil(rule_element->first_child);
+            if(has_children)
+            {
+                ExpandRule(rule_element, out_strings, cur_node, allowed);
+            }
+            else
+            {
+                if(rule_element->flags & MD_NodeFlag_CharLiteral)   // NOTE(mal): Terminal production
+                {
+                    char c = 0;
+                    if(rule_element->string.size == 2 && rule_element->string.str[0] == '\\')
+                    {
+                        switch(rule_element->string.str[1]){
+                          case '\\': c = '\\';  break;
+                          case '\'': c = '\'';  break;
+                          case '"':  c = '\"';  break;
+                        }
+                    }
+                    else
+                    {
+                        c = rule_element->string.str[0];
+                    }
+
+                    MD_String8 character = MD_PushStringF("%c", c);
+                    MD_PushStringToList(out_strings, character);
+
+                    if(allowed & AllowedOperationFlag_Leaf)
+                    {
+                        Extend(&cur_node->whole_string, c);
+                        if(!MD_NodeHasTag(rule_element, MD_S8Lit("delimiter")))
+                        {
+                            Extend(&cur_node->string, c);
+                        }
+                    }
+                    else if(allowed & AllowedOperationFlag_Tag)
+                    {
+                        Extend(&cur_node->whole_string, c);
+                        if(c != '@')
+                        {
+                            Extend(&cur_node->string, c);
+                        }
+                    }
+                }
+                else        // NOTE(mal): Non-terminal production
+                {
+                    MD_Node *node_to_tag = 0;
+                    if(MD_NodeHasTag(rule_element, MD_S8Lit("child")))
+                    {
+                        cur_node = NewChild(cur_node);
+                    }
+                    else if(MD_NodeHasTag(rule_element, MD_S8Lit("sibling")))
+                    {
+                        cur_node = NewChild(cur_node->parent);
+                    }
+                    else if(MD_NodeHasTag(rule_element, MD_S8Lit("leaf")))
+                    {
+                        allowed |= AllowedOperationFlag_Leaf;
+                    }
+                    else if(MD_NodeHasTag(rule_element, MD_S8Lit("tag")))
+                    {
+                        allowed |= AllowedOperationFlag_Tag;
+                        node_to_tag = cur_node;
+                        cur_node = NewChild(0);
+                        cur_node->kind = MD_NodeKind_Tag;
+                    }
+
+                    MD_Node * production = MD_NodeTable_Lookup(globals.production_table, rule_element->string)->node;
+                    MD_Assert(production);
+
+                    ExpandProduction(production, out_strings, cur_node, allowed);
+                    if(node_to_tag)
+                    {
+                        MD_PushTag(node_to_tag, cur_node);
+                        cur_node = node_to_tag;
+                    }
+
+                    if(MD_NodeHasTag(rule_element, MD_S8Lit("leaf")))
+                    {
+                        allowed &= ~AllowedOperationFlag_Leaf;
+                    }
+                    else if(MD_NodeHasTag(rule_element, MD_S8Lit("tag")))
+                    {
+                        allowed &= ~AllowedOperationFlag_Tag;
+                    }
+                }
+            }
+        }
+    }
+}
+
+static void ExpandProduction(MD_Node *production, MD_String8List *out, MD_Node *cur_node, AllowedOperationFlags allowed)
+{
+    MD_i64 rule_count = MD_ChildCountFromNode(production);
+    int rule_number = rand_U32(globals.random_series)%rule_count;
+    MD_Node *rule = MD_ChildFromIndex(production, rule_number);
+    ExpandRule(rule, out, cur_node, allowed);
+}
+
+static MD_Node * FindNonTerminalProduction(MD_Node *node, MD_NodeTable *visited)
+{
+    MD_Node *result = 0;
+
+    MD_b32 should_visit = 1;
+    if(!MD_NodeIsNil(node->first_child) && node->string.size)
+    {
+        if(MD_NodeTable_Lookup(visited, node->string))
+        {
+            should_visit = 0;
+        }
+        else
+        {
+            MD_b32 inserted = MD_NodeTable_Insert(visited, MD_NodeTableCollisionRule_Overwrite, node->string, node);
+            MD_Assert(inserted);
+        }
+    }
+
+    if(should_visit)
+    {
+        if(MD_NodeIsNil(node->first_child))
+        {
+            if(node->flags & MD_NodeFlag_CharLiteral)
+            {
+            }
+            else
+            {
+                MD_NodeTableSlot *slot = MD_NodeTable_Lookup(globals.production_table, node->string);
+                if(slot)
+                {
+                    MD_Node *production = slot->node;
+                    result = FindNonTerminalProduction(production, visited);
+                }
+                else
+                {
+                    result = node;
+                }
+            }
+        }
+        else
+        {
+            for(MD_EachNode(child, node->first_child))
+            {
+                result = FindNonTerminalProduction(child, visited);
+                if(result)
+                {
+                    break;
+                }
+            }
+        }
+    }
+
+    return result;
+}
+
+static MD_b32 EqualTrees(MD_Node *a, MD_Node *b);
+static MD_b32 EqualList(MD_Node *a, MD_Node *b)
+{
+    MD_b32 result = 1;
+
+    while(!MD_NodeIsNil(a) && !MD_NodeIsNil(b))
+    {
+        if(!EqualTrees(a, b))
+        {
+            result = 0;
+        }
+        a = a->next;
+        b = b->next;
+    }
+
+    return result;
+}
+static MD_b32 EqualTrees(MD_Node *a, MD_Node *b)
+{
+    MD_b32 result = (a->kind == b->kind && MD_StringMatch(a->string, b->string, 0) && 
+                     MD_StringMatch(a->string, b->string, 0));
+    result &= EqualList(a->first_tag, b->first_tag);
+    result &= EqualList(a->first_child, b->first_child);
+    return result;
+}
+
+int main(int argument_count, char **arguments)
+{
+    MD_Node *grammar = MD_ParseWholeFile(MD_S8Lit("tests/grammar.md"));
+
+    // NOTE(mal): In order to get a BNF-like syntax, I feed the MD output through two transformations:
+    //            1) Tag []-style sets as optional 
+    MD_Node *optional_tag = 0;
+    {
+        MD_ParseResult parse_result = MD_ParseOneNode(MD_S8Lit(""), MD_S8Lit("@"OPTIONAL_TAG" is_a_tag"));
+        optional_tag = parse_result.node->first_tag;
+    }
+    TagSquareBracketSetsAsOptional(grammar, optional_tag);
+
+    // NOTE(mal): 2) Divide rules around '|' operators and transplant them into a new tree structure
+    //               productions > production > rules > rule > rule_element
+    MD_Node *productions = NewChild(0);
+    for(MD_EachNode(symbol, grammar->first_child))
+    {
+        MD_Node *production = NewChildLabel(productions, symbol->string);
+        MD_Node *rule = NewChild(production);
+        for(MD_Node *rule_element = symbol->first_child; !MD_NodeIsNil(rule_element); )
+        {
+            MD_Node *next = rule_element->next;
+
+            MD_b32 has_children = !MD_NodeIsNil(rule_element->first_child);
+            if(has_children)
+            {
+                MD_PushChild(rule, rule_element);
+            }
+            else
+            {
+                if(MD_StringMatch(rule_element->string, MD_S8Lit("|"), 0) && 
+                   !(rule_element->flags & MD_NodeFlag_CharLiteral))
+                {
+                    rule = NewChild(production);
+                }
+                else
+                {
+                    MD_PushChild(rule, rule_element);
+                }
+            }
+
+            rule_element = next;
+        }
+    }
+
+    // NOTE(mal): Debug rules after transformations
+#if 0
+    for(MD_EachNode(production, productions->first_child))
+    {
+        printf("%.*s: \n", MD_StringExpand(production->string));
+
+        for(MD_EachNode(rule, production->first_child))
+        {
+            printf("    ");
+            PrintRule(rule);
+            printf("\n");
+        }
+    }
+#endif
+
+    // NOTE(mal): Build production hash table
+    MD_NodeTable production_table_ = {0};
+    globals.production_table = &production_table_;
+    for(MD_EachNode(production, productions->first_child))
+    {
+        MD_b32 inserted = MD_NodeTable_Insert(globals.production_table, MD_NodeTableCollisionRule_Overwrite, 
+                                              production->string, production);
+        MD_Assert(inserted);
+    }
+
+    // NOTE(mal): Check for root production
+    MD_Node* file_production = MD_NodeTable_Lookup(globals.production_table, MD_S8Lit("file"))->node;
+    if(!file_production)
+    {
+        fprintf(stderr, "Error: Grammar file does not specify \"file\" production\n");
+        goto error;
+    }
+
+    // NOTE(mal): Check that all branches lead to terminal nodes
+    MD_NodeTable visited_productions = {0};
+    MD_Node *non_terminal_production = FindNonTerminalProduction(file_production, &visited_productions);
+    if(non_terminal_production)
+    {
+        fprintf(stderr, "Error: Non-terminal production \"%.*s\"\n", MD_StringExpand(non_terminal_production->string));
+        goto error;
+    }
+
+    // NOTE(mal): Check that all productions are reachable
+    for(MD_EachNode(production, productions->first_child))
+    {
+        MD_NodeTableSlot *slot = MD_NodeTable_Lookup(&visited_productions, production->string);
+        if(!slot)
+        {
+            fprintf(stderr, "Warning: Unreachable production \"%.*s\"\n", MD_StringExpand(production->string));
+        }
+    }
+
+    RandomSeries random_series = rand_seed(0, 0);  // NOTE(mal): Reproduceable
+    globals.random_series = &random_series;
+
+    MD_Node* node = MD_NodeTable_Lookup(globals.production_table, MD_S8Lit("file"))->node;
+    MD_u32 test_count = 1000;
+    for(int i = 0; i < test_count; ++i){
+        MD_String8List expanded_list = {0};
+
+        // NOTE(mal): Generate a random MD file
+        MD_Node *file_control_node = NewChild(0);
+        file_control_node->kind = MD_NodeKind_File;
+        ExpandProduction(node, &expanded_list, file_control_node, 0);
+        MD_String8 expanded = MD_JoinStringList(expanded_list);
+
+        MD_Node *file_node = MD_ParseWholeString(MD_S8Lit(""), expanded);
+        file_node->string = file_node->whole_string = (MD_String8){0};
+
+        printf("Test %d: ", i);
+        printf("> %.*s <\n", MD_StringExpand(expanded));
+        if(!EqualTrees(file_node, file_control_node))
+        {
+            printf("\nFailed test %d\n", i);
+            printf("MD:\n");
+            MD_OutputTree(stdout, file_node);
+            printf("Grammar:\n");
+            MD_OutputTree(stdout, file_control_node); printf("\n");
+
+            return -1;
+        }
+    }
+
+    printf("Passed %d tests\n", test_count);
+    
+    error:
+    
+    return 0;
+}
diff --git a/tests/grammar.md b/tests/grammar.md
new file mode 100644
index 0000000..467da71
--- /dev/null
+++ b/tests/grammar.md
@@ -0,0 +1,75 @@
+/* MetaDesk grammar with semantic annotations
+ *
+ * Each line represents a BNF-esque production of the form:
+ *      symbol : rule_1 | ... | rule_n
+ * - Pipe signs indicate mutually exclusive alternatives
+ * - Square quotes denote optional rules
+ * - Character literals are terminal productions
+ * - Tags indicate which way the productions attach to the generated tree (@child, @sibling, @leaf, @tag)
+ *   and miscellaneous semantics (@delimiter)
+ */
+
+file            : [@child set_list]
+set_list        : tagged_named_set [' ' @sibling set_list]
+tagged_named_set: { [tag_list] set }
+tag_list        : @tag tag ' ' [tag_list]
+tag             : '@' identifier        // TODO(mal): tag parameters
+set             : @leaf leaf | '{' [@child set_list] '}'
+leaf            : identifier | integer_literal | char_literal | string_literal  // TODO(mal): Also symbol_label
+identifier      : alpha [alphanumeric]  // TODO(mal): I think we should allow leading underscores
+alphanumeric    : alpha [alphanumeric] | digit [alphanumeric] | '_' [alphanumeric]
+
+integer_literal : { ['-'] natural_literal }
+natural_literal : digit [natural_literal]
+
+char_literal                    : @delimiter '\'' [char_literal_items] @delimiter '\''
+char_literal_items              : char_literal_item [char_literal_items]
+char_literal_item               : ascii_no_backslash_no_quotes | '"' | '\\' ascii
+ascii                           : ascii_no_backslash_no_quotes | '\'' | '"' | '\\'
+ascii_no_backslash_no_quotes    : digit | alpha | symbol_no_backslash_no_quotes | space
+symbol_no_backslash_no_quotes   : symbol_no_backslash_no_quotes_1 | symbol_no_backslash_no_quotes_2
+symbol_no_backslash_no_quotes_1 : '!'|'#'|'$'|'%'|'&'|'('|')'|'*'|'+'|','|'-'|'.'|'/'|':'|';'
+symbol_no_backslash_no_quotes_2 : '<'|'='|'>'|'?'|'@'|'['|']'|'^'|'_'|'`'|'{'|'|'|'}'|'~'
+
+string_literal                  : @delimiter '"' [string_literal_items] @delimiter '"'
+string_literal_items            : string_literal_item [string_literal_items]
+string_literal_item             : ascii_no_backslash_no_quotes | '\'' | '\\' ascii
+
+digit           : '0'|'1'|'2'|'3'|'4'|'5'|'6'|'7'|'8'|'9'
+alpha           : lowercase | uppercase
+lowercase       : 'a'|'b'|'c'|'d'|'e'|'f'|'g'|'h'|'i'|'j'|'k'|'l'|'m'|'n'|'o'|'p'|'q'|'r'|'s'|'t'|'u'|'v'|'w'|'z'|'y'|'z'
+uppercase       : 'A'|'B'|'C'|'D'|'E'|'F'|'G'|'H'|'I'|'J'|'K'|'L'|'M'|'N'|'O'|'P'|'Q'|'R'|'S'|'T'|'U'|'V'|'W'|'Z'|'Y'|'Z'
+space           : ' '
+
+symbol_label    : '~'|'!'|'%'|'^'|'&'|'*'|'+'|'-'|'/'|'|'|'<'|'>'|'$'|'='|'.'|'?'|'_'|'\\'
+
+/*
+
+symbol_no_quote : symbol_label | symbol_colon | symbol_group
+
+symbol          : symbol_label | symbol_colon | symbol_group
+
+symbol_group    : symbol_open | symbol_close
+symbol_open     : '(' | '[' | '{'
+symbol_close    : ')' | ']' | '}' 
+
+escaped_char    : '\\' '\\' | '\\' '\'' | '\\' '\"'
+symbol_colon    : ':'
+
+*/
+
+
+/*
+    // NOTE(mal): I think this one should work too, but MD only delimits top level constructs with newlines
+    file            : [@child set_list]
+    set_list        : set [',' @sibling set_list]
+    set             : @leaf element | '{' [@child set_list] '}'
+    element         : 'A'
+
+    // NOTE(mal): This is the simples grammar that works
+    file            : [@child set_list]
+    set_list        : set ['\n' @sibling set_list]
+    set             : @leaf element | '{' [@child set_list] '}'
+    element         : 'A'
+*/
+