diff --git a/hex.py b/hex.py
new file mode 100644
index 0000000..dbd99fd
--- /dev/null
+++ b/hex.py
@@ -0,0 +1,121 @@
+class HexCalculator:
+    """
+    Hexadecimal calculator module.
+
+    Supports:
+    - Hex ↔ Decimal conversions
+    - Arithmetic operations in HEX
+    - Complement calculations
+    - Input validation
+    """
+
+    def _validate_hex(self, value: str) -> str:
+        """
+        Validate input format H'AB12'
+        Returns the internal hex string.
+        """
+        if not isinstance(value, str):
+            raise ValueError("Input must be a string")
+
+        if not value.startswith("H'") or not value.endswith("'"):
+            raise ValueError("Invalid HEX format. Expected H'AB12'")
+
+        hex_part = value[2:-1]
+
+        try:
+            int(hex_part, 16)
+        except ValueError:
+            raise ValueError("Invalid hexadecimal digits")
+
+        return hex_part
+
+    # -------------------------------
+    # Sravanti will edit this part
+    # -------------------------------
+    def hex_to_decimal(self, value: str) -> str:
+        """
+        Convert HEX → Decimal
+
+        Example:
+        H'1A5' → D'421'
+        """
+        raise NotImplementedError("hex_to_decimal not implemented yet")
+
+    # -------------------------------
+    # Saichaitanya will edit this part
+    # -------------------------------
+    def decimal_to_hex(self, value: str) -> str:
+        value = value.strip()
+
+        if value.startswith("D'") and value.endswith("'"):
+            value = value[2:-1]
+
+        if not value.isdigit():
+            raise ValueError("Invalid decimal input")
+
+        return f"H'{hex(int(value))[2:].upper()}'"
+    # -------------------------------
+    # Joydip will edit this part
+    # -------------------------------
+    def add(self, a: str, b: str) -> str:
+        """
+        HEX addition
+
+        Example:
+        H'A' + H'5' → H'F'
+        """
+        raise NotImplementedError("add not implemented yet")
+    # -------------------------------
+    # Pratyush will edit this part
+    # -------------------------------
+    
+    def subtract(self, a: str, b: str) -> str:
+        """
+        HEX subtraction
+        """
+        hex_a = self._validate_hex(a)
+        hex_b = self._validate_hex(b)
+
+        result = int(hex_a, 16) - int(hex_b, 16)
+
+        if result < 0:
+            return f"H'-{format(abs(result), 'X')}'"
+
+        return f"H'{format(result, 'X')}'"
+
+    # -------------------------------
+    # Sneha will edit this part
+    # -------------------------------
+    def fifteen_complement(self, value: str) -> str:
+        """
+        Compute 15's complement
+        """
+        hex_part = self._validate_hex(value)
+
+        result = ""
+        for digit in hex_part:
+            comp = 15 - int(digit, 16)
+            result += format(comp, 'X')
+
+        return f"H'{result}'"
+
+
+    def sixteen_complement(self, value: str) -> str:
+        """
+        Compute 16's complement
+        """
+        hex_part = self._validate_hex(value)
+
+        # Step 1: 15's complement
+        comp15 = ""
+        for digit in hex_part:
+            comp = 15 - int(digit, 16)
+            comp15 += format(comp, 'X')
+
+        # Step 2: add 1
+        comp16 = hex(int(comp15, 16) + 1)[2:].upper()
+
+        # Step 3: maintain same length
+        comp16 = comp16.zfill(len(hex_part))
+
+        return f"H'{comp16}'"
diff --git a/readme.md b/readme.md
new file mode 100644
index 0000000..e965047
--- /dev/null
+++ b/readme.md
@@ -0,0 +1 @@
+Hello
diff --git a/test_hex.py b/test_hex.py
new file mode 100644
index 0000000..ef6c4dd
--- /dev/null
+++ b/test_hex.py
@@ -0,0 +1,88 @@
+# test_hex.py
+
+import unittest
+from hex import HexCalculator
+
+
+class TestHexCalculator(unittest.TestCase):
+
+    def setUp(self):
+        self.hex_calc = HexCalculator()
+
+    # ---------------------------------
+    # SRAVANTI 1 TESTS
+    # ---------------------------------
+    def test_hex_to_decimal(self):
+        self.assertEqual(
+            self.hex_calc.hex_to_decimal("H'1A5'"),
+            "D'421'"
+        )
+
+    # ---------------------------------
+    # SAICHAITANYA 2 TESTS
+    # ---------------------------------
+    def test_decimal_to_hex(self):
+        self.assertEqual(
+            self.hex_calc.decimal_to_hex("D'243'"),
+            "H'F3'"
+        )
+    def test_decimal_to_hex_small(self):
+    self.assertEqual(
+        self.hex_calc.decimal_to_hex("D'15'"),
+        "H'F'"
+        )
+    # ---------------------------------
+    # JOYDIP 3 TESTS
+    # ---------------------------------
+    def test_add(self):
+        self.assertEqual(
+            self.hex_calc.add("H'A'", "H'5'"),
+            "H'F'"
+        )
+    # ---------------------------------
+    # PRATYUSH 3 TESTS
+    # ---------------------------------
+    
+    def test_subtract(self):
+        self.assertEqual(
+            self.hex_calc.subtract("H'F'", "H'5'"),
+            "H'A'"
+        )
+
+    def test_subtract_with_borrow(self):
+        self.assertEqual(
+            self.hex_calc.subtract("H'10'", "H'1'"),
+            "H'F'"
+        )
+
+    def test_subtract_negative_result(self):
+        self.assertEqual(
+            self.hex_calc.subtract("H'2'", "H'5'"),
+            "H'-3'"
+        )
+
+    # ---------------------------------
+    # SNEHA 4 TESTS
+    # ---------------------------------
+    def test_fifteen_complement(self):
+        self.assertEqual(
+            self.hex_calc.fifteen_complement("H'A'"),
+            "H'5'"
+        )
+
+    def test_sixteen_complement(self):
+        self.assertEqual(
+            self.hex_calc.sixteen_complement("H'A'"),
+            "H'6'"
+        )
+
+    # ---------------------------------
+    # COMMON VALIDATION TEST --- Already Done
+    # ---------------------------------
+    def test_invalid_hex(self):
+        with self.assertRaises(ValueError):
+            self.hex_calc.hex_to_decimal("123")
+
+
+if __name__ == "__main__":
+    unittest.main()