diff --git a/tools/BSExpressions/BSExpressions.g4 b/tools/BSExpressions/BSExpressions.g4
new file mode 100644
index 0000000000..941393848e
--- /dev/null
+++ b/tools/BSExpressions/BSExpressions.g4
@@ -0,0 +1,70 @@
+grammar BSExpressions;
+
+// Define tokens
+OR_OP : '||';
+AND_OP : '&&';
+NOT_OP : '!';
+COMP_OP : '==' | '!=' | '<' | '<=' | '>' | '>=';
+ADD_OP : '+' | '-';
+MUL_OP : '*' | '/';
+EXP_OP : '**';
+LPAR : '(';
+RPAR : ')';
+LSQR : '[';
+RSQR : ']';
+DOT : '.';
+
+// Define literals
+LITERAL : (NUMBER | QUOTED_STRING);
+NUMBER : INT | FLOAT;
+INT : ('+' | '-')? DIGIT+;
+FLOAT : ('+' | '-')? DIGIT+ '.' DIGIT+;
+DIGIT : [0-9];
+QUOTED_STRING : '"' (ESC | ~["\\])* '"';
+ESC : '\\' ["\\/bfnrt];
+BOOL : 'True' | 'False';
+NULL : 'None';
+
+// Define rules
+start : expression EOF;
+
+expression : test;
+
+test : andTest (OR_OP andTest)*;
+
+andTest : notTest (AND_OP notTest)*;
+
+notTest : NOT_OP notTest | comparison;
+
+comparison : expr (COMP_OP expr)*;
+
+expr : term (ADD_OP term)*;
+
+term : factor (MUL_OP factor)*;
+
+factor : atom (EXP_OP factor)?;
+
+atom : item (trailer)*;
+
+item : parenthetical | array | obj_literal | identifier | LITERAL;
+
+parenthetical : LPAR test RPAR;
+
+array : LSQR (test (',' test)*)? RSQR;
+
+obj_literal : '{}';
+
+trailer : function_call | array_lookup | object_lookup;
+
+function_call : LPAR (test (',' test)*)? RPAR;
+
+array_lookup : LSQR test RSQR;
+
+object_lookup : DOT identifier;
+
+identifier : IDENT_START IDENT_PART*;
+
+fragment IDENT_START : [a-zA-Z_];
+fragment IDENT_PART : [a-zA-Z_0-9];
+
+WS : [ \t\r\n]+ -> skip;