diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..c39f42e
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,32 @@
+# Changelog
+
+- [0.0.4](#004)
+
+## 0.0.4
+
+### [Fix incorrect state mutability identification](https://github.com/OpenZeppelin/sgp/pull/9)
+
+This PR fixed incorrect state mutability identification for the various structures, such as:
+
+**`const` state mutability for the state variable declaration**
+
+```solidity
+contract Example {
+    uint256 constant x = 1;
+}
+```
+
+**`payable` state mutability for the function return parameter variable declaration**
+
+```solidity
+function test() public returns(address payable) {}
+```
+
+Now, these cases are handled correctly after the bug in the version `0.0.3`.
+
+### [CHANGELOG.md](/CHANGELOG.md) added
+
+### [Onboard `ruff](https://github.com/OpenZeppelin/sgp/pull/10)
+
+- Use `ruff` for the `py` files check and formatting.
+- Added a `ruff_helper.sh` script
diff --git a/pyproject.toml b/pyproject.toml
index 9c65a70..edd34dd 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "openzeppelin-solidity-grammar-parser"
-version = "0.0.3"
+version = "0.0.4"
 authors = [{ name = "Georgii Plotnikov", email = "accembler@gmail.com" }]
 description = "Solidity ANTLR4 grammar Python parser"
 readme = "README.md"
@@ -49,3 +49,6 @@ exclude = '''
     )/
 )
 '''
+
+[tool.ruff]
+exclude = ["./sgp/parser/"]
diff --git a/requirements.txt b/requirements.txt
index 614c4c0..e0ac19c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,3 +3,4 @@ coverage==7.3.1
 simplejson==3.19.1
 typing==3.7.4.3
 typing_extensions==4.8.0
+ruff==0.2.1
diff --git a/ruff_helper.sh b/ruff_helper.sh
new file mode 100755
index 0000000..c5fcf2b
--- /dev/null
+++ b/ruff_helper.sh
@@ -0,0 +1,7 @@
+#!/bin/bash
+
+source ./bin/activate
+pip install ruff
+
+ruff check .
+ruff format .
diff --git a/sgp/ast_node_types.py b/sgp/ast_node_types.py
index c2ff46a..3178b41 100644
--- a/sgp/ast_node_types.py
+++ b/sgp/ast_node_types.py
@@ -1,4 +1,4 @@
-from typing import Any, List, Optional, Tuple, Union, Dict
+from typing import List, Optional, Tuple, Union
 
 
 class Position:
diff --git a/sgp/main.py b/sgp/main.py
index 732a1b3..e9b25c3 100644
--- a/sgp/main.py
+++ b/sgp/main.py
@@ -1,5 +1,6 @@
 import sgp_parser
 
+
 def main():
     input = """
 // SPDX-License-Identifier: MIT
@@ -19,5 +20,6 @@ def main():
     except Exception as e:
         print(e)
 
-if __name__ == '__main__':
+
+if __name__ == "__main__":
     main()
diff --git a/sgp/sgp_error_listener.py b/sgp/sgp_error_listener.py
index eaf7b11..2d9f669 100644
--- a/sgp/sgp_error_listener.py
+++ b/sgp/sgp_error_listener.py
@@ -2,6 +2,7 @@
 from typing_extensions import override
 from antlr4.error.ErrorListener import ErrorListener
 
+
 class SGPError:
     def __init__(self, message, line, column):
         self.message = message
@@ -11,6 +12,7 @@ def __init__(self, message, line, column):
     def __str__(self):
         return f"{self.message} ({self.line}:{self.column})"
 
+
 class SGPErrorListener(ErrorListener):
     def __init__(self):
         super().__init__()
diff --git a/sgp/sgp_parser.py b/sgp/sgp_parser.py
index b46c6ae..e7d7bb7 100644
--- a/sgp/sgp_parser.py
+++ b/sgp/sgp_parser.py
@@ -1,6 +1,5 @@
 import os
 import simplejson
-from typing import Dict
 
 from antlr4.CommonTokenStream import CommonTokenStream
 from antlr4.InputStream import InputStream as ANTLRInputStream
@@ -17,14 +16,14 @@
 
 class ParserError(Exception):
     """
-    An exception raised when the parser encounters an error.            
+    An exception raised when the parser encounters an error.
     """
 
     def __init__(self, errors) -> None:
         """
         Parameters
         ----------
-        errors : List[Dict[str, Any]] - A list of errors encountered by the parser.        
+        errors : List[Dict[str, Any]] - A list of errors encountered by the parser.
         """
         super().__init__()
         error = errors[0]
@@ -50,7 +49,7 @@ def parse(
 
     Returns
     -------
-    SourceUnit - The root of an AST of the Solidity source string.    
+    SourceUnit - The root of an AST of the Solidity source string.
     """
 
     input_stream = ANTLRInputStream(input_string)
@@ -69,7 +68,7 @@ def parse(
     ast_builder = SGPVisitor(options)
     try:
         source_unit: SourceUnit = ast_builder.visit(source_unit)
-    except Exception as e:
+    except Exception:
         raise Exception("AST was not generated")
     else:
         if source_unit is None:
diff --git a/sgp/sgp_visitor.py b/sgp/sgp_visitor.py
index b805cde..a271a94 100644
--- a/sgp/sgp_visitor.py
+++ b/sgp/sgp_visitor.py
@@ -1392,7 +1392,9 @@ def visitAssemblyCall(self, ctx: SP.AssemblyCallContext) -> AssemblyCall:
 
         return self._add_meta(node, ctx)
 
-    def visitAssemblyLiteral(self, ctx: SP.AssemblyLiteralContext) -> Union[
+    def visitAssemblyLiteral(
+        self, ctx: SP.AssemblyLiteralContext
+    ) -> Union[
         StringLiteral,
         BooleanLiteral,
         DecimalNumber,
diff --git a/sgp/tokens.py b/sgp/tokens.py
index 059eeb9..11eb58e 100644
--- a/sgp/tokens.py
+++ b/sgp/tokens.py
@@ -1,8 +1,10 @@
 from typing import List, Dict, Any
 
+
 def rsplit(input_string: str, value: str) -> List[str]:
     index = input_string.rfind(value)
-    return [input_string[:index], input_string[index + 1:]]
+    return [input_string[:index], input_string[index + 1 :]]
+
 
 def normalize_token_type(value: str) -> str:
     if value.endswith("'"):
@@ -11,68 +13,80 @@ def normalize_token_type(value: str) -> str:
         value = value[1:]
     return value
 
+
 def get_token_type(value: str) -> str:
     TYPE_TOKENS = [
-        'var',
-        'bool',
-        'address',
-        'string',
-        'Int',
-        'Uint',
-        'Byte',
-        'Fixed',
-        'UFixed',
+        "var",
+        "bool",
+        "address",
+        "string",
+        "Int",
+        "Uint",
+        "Byte",
+        "Fixed",
+        "UFixed",
     ]
 
-    if value in ['Identifier', 'from']:
-        return 'Identifier'
-    elif value in ['TrueLiteral', 'FalseLiteral']:
-        return 'Boolean'
-    elif value == 'VersionLiteral':
-        return 'Version'
-    elif value == 'StringLiteral':
-        return 'String'
+    if value in ["Identifier", "from"]:
+        return "Identifier"
+    elif value in ["TrueLiteral", "FalseLiteral"]:
+        return "Boolean"
+    elif value == "VersionLiteral":
+        return "Version"
+    elif value == "StringLiteral":
+        return "String"
     elif value in TYPE_TOKENS:
-        return 'Type'
-    elif value == 'NumberUnit':
-        return 'Subdenomination'
-    elif value == 'DecimalNumber':
-        return 'Numeric'
-    elif value == 'HexLiteral':
-        return 'Hex'
-    elif value == 'ReservedKeyword':
-        return 'Reserved'
+        return "Type"
+    elif value == "NumberUnit":
+        return "Subdenomination"
+    elif value == "DecimalNumber":
+        return "Numeric"
+    elif value == "HexLiteral":
+        return "Hex"
+    elif value == "ReservedKeyword":
+        return "Reserved"
     elif not value.isalnum():
-        return 'Punctuator'
+        return "Punctuator"
     else:
-        return 'Keyword'
+        return "Keyword"
+
 
 def get_token_type_map(tokens: str) -> Dict[int, str]:
-    lines = tokens.split('\n')
+    lines = tokens.split("\n")
     token_map = {}
 
     for line in lines:
-        value, key = rsplit(line, '=')
+        value, key = rsplit(line, "=")
         token_map[int(key)] = normalize_token_type(value)
 
     return token_map
 
-#TODO: sort it out
-def build_token_list(tokens_arg: List[Dict[str, Any]], options: Dict[str, Any]) -> List[Dict[str, Any]]:
+
+# TODO: sort it out
+def build_token_list(
+    tokens_arg: List[Dict[str, Any]], options: Dict[str, Any]
+) -> List[Dict[str, Any]]:
     token_types = get_token_type_map(tokens_arg)
     result = []
 
     for token in tokens_arg:
-        type_str = get_token_type(token_types[token['type']])
-        node = {'type': type_str, 'value': token['text']}
+        type_str = get_token_type(token_types[token["type"]])
+        node = {"type": type_str, "value": token["text"]}
 
-        if options.get('range', False):
-            node['range'] = [token['startIndex'], token['stopIndex'] + 1]
+        if options.get("range", False):
+            node["range"] = [token["startIndex"], token["stopIndex"] + 1]
 
-        if options.get('loc', False):
-            node['loc'] = {
-                'start': {'line': token['line'], 'column': token['charPositionInLine']},
-                'end': {'line': token['line'], 'column': token['charPositionInLine'] + len(token['text']) if token['text'] else 0}
+        if options.get("loc", False):
+            node["loc"] = {
+                "start": {"line": token["line"], "column": token["charPositionInLine"]},
+                "end": {
+                    "line": token["line"],
+                    "column": (
+                        token["charPositionInLine"] + len(token["text"])
+                        if token["text"]
+                        else 0
+                    ),
+                },
             }
 
         result.append(node)
diff --git a/sgp/utils.py b/sgp/utils.py
index 5da9129..c4cb94c 100644
--- a/sgp/utils.py
+++ b/sgp/utils.py
@@ -1,6 +1,3 @@
-from typing import Any
-
-
 def string_from_snake_to_camel_case(input: str) -> str:
     """
     Convert a string from snake_case to camelCase.
diff --git a/test/test_misc/test_misc.py b/test/test_misc/test_misc.py
index 819fd38..7711eca 100644
--- a/test/test_misc/test_misc.py
+++ b/test/test_misc/test_misc.py
@@ -5,27 +5,7 @@
 
 class TestMisc(unittest.TestCase):
     def test_misc(self) -> None:
-        input = """contract Example4 {
-    /// @custom:storage-location erc7201:example.main
-    struct MainStorage {
-        uint256 x;
-        uint256 y;
-    }
-
-    // keccak256(abi.encode(uint256(keccak256("example.main")) - 1)) & ~bytes32(uint256(0xff));
-    bytes32 private constant MAIN_STORAGE_LOCATION =
-        0x183a6125c38840424c4a85fa12bab2ab606c4b6d0e7cc73c0c06ba5300eab500;
-
-    uint256 constant x = 1;
-
-    function _getMainStorage() private pure returns (MainStorage storage $) {
-        assembly {
-            $.slot := MAIN_STORAGE_LOCATION
-        }
-    }
-}"""
+        input = """function add_your_solidity_code_here {}"""
 
         ast = parse(input)
         self.assertIsNotNone(ast)
-        self.assertTrue(ast.children[0].children[1].variables[0].is_declared_const)
-        self.assertTrue(ast.children[0].children[2].variables[0].is_declared_const)
diff --git a/test/test_parsing/test_parsing.py b/test/test_parsing/test_parsing.py
index 3da1618..d35264a 100644
--- a/test/test_parsing/test_parsing.py
+++ b/test/test_parsing/test_parsing.py
@@ -6,8 +6,8 @@
 from sgp.sgp_parser import parse
 from sgp.utils import string_from_snake_to_camel_case
 
-class TestParsing(unittest.TestCase):
 
+class TestParsing(unittest.TestCase):
     def test_parsing(self):
         current_directory = pathlib.Path(__file__).parent.resolve()
 
@@ -23,12 +23,10 @@ def test_parsing(self):
 
         res = parse(test_content, dump_json=True)
         ast_actual = simplejson.dumps(
-                res,
-                default=lambda obj: {
-                    string_from_snake_to_camel_case(k): v
-                    for k, v in obj.__dict__.items()
-                },
-            )
-        
+            res,
+            default=lambda obj: {
+                string_from_snake_to_camel_case(k): v for k, v in obj.__dict__.items()
+            },
+        )
+
         self.assertEqual(ast_expected, ast_actual)
-        
\ No newline at end of file