diff --git a/robot/resources/lib/python_keywords/json_transformers.py b/robot/resources/lib/python_keywords/json_transformers.py
index c1554b3..317383e 100644
--- a/robot/resources/lib/python_keywords/json_transformers.py
+++ b/robot/resources/lib/python_keywords/json_transformers.py
@@ -1,5 +1,3 @@
-#!/usr/bin/python3.9
-
 """
     When doing requests to NeoFS, we get JSON output as an automatically decoded
     structure from protobuf. Some fields are decoded with boilerplates and binary
@@ -14,25 +12,24 @@ import base64
 import base58
 
 
-def decode_simple_header(data: dict):
+def decode_simple_header(data: dict) -> dict:
     """
     This function reencodes Simple Object header and its attributes.
     """
     try:
         data = decode_common_fields(data)
 
-        # object attributes view normalization
-        ugly_attrs = data["header"]["attributes"]
-        data["header"]["attributes"] = {}
-        for attr in ugly_attrs:
-            data["header"]["attributes"][attr["key"]] = attr["value"]
+        # Normalize object attributes
+        data["header"]["attributes"] = {
+            attr["key"]: attr["value"] for attr in data["header"]["attributes"]
+        }
     except Exception as exc:
         raise ValueError(f"failed to decode JSON output: {exc}") from exc
 
     return data
 
 
-def decode_split_header(data: dict):
+def decode_split_header(data: dict) -> dict:
     """
     This function rearranges Complex Object header.
     The header holds SplitID, a random unique
@@ -49,35 +46,25 @@ def decode_split_header(data: dict):
     return data
 
 
-def decode_linking_object(data: dict):
+def decode_linking_object(data: dict) -> dict:
     """
     This function reencodes Linking Object header.
     It contains IDs of child Objects and Split Chain data.
     """
     try:
         data = decode_simple_header(data)
-        # reencoding Child Object IDs
-        # { 'value': <Base58 encoded OID> } -> <Base64 encoded OID>
-        for ind, val in enumerate(data["header"]["split"]["children"]):
-            data["header"]["split"]["children"][ind] = json_reencode(val["value"])
-        data["header"]["split"]["splitID"] = json_reencode(data["header"]["split"]["splitID"])
-        data["header"]["split"]["previous"] = (
-            json_reencode(data["header"]["split"]["previous"]["value"])
-            if data["header"]["split"]["previous"]
-            else None
-        )
-        data["header"]["split"]["parent"] = (
-            json_reencode(data["header"]["split"]["parent"]["value"])
-            if data["header"]["split"]["parent"]
-            else None
-        )
+        split = data["header"]["split"]
+        split["children"] = [json_reencode(item["value"]) for item in split["children"]]
+        split["splitID"] = json_reencode(split["splitID"])
+        split["previous"] = json_reencode(split["previous"]["value"]) if split["previous"] else None
+        split["parent"] = json_reencode(split["parent"]["value"]) if split["parent"] else None
     except Exception as exc:
         raise ValueError(f"failed to decode JSON output: {exc}") from exc
 
     return data
 
 
-def decode_storage_group(data: dict):
+def decode_storage_group(data: dict) -> dict:
     """
     This function reencodes Storage Group header.
     """
@@ -89,7 +76,7 @@ def decode_storage_group(data: dict):
     return data
 
 
-def decode_tombstone(data: dict):
+def decode_tombstone(data: dict) -> dict:
     """
     This function reencodes Tombstone header.
     """
@@ -101,29 +88,27 @@ def decode_tombstone(data: dict):
     return data
 
 
-def decode_session_token(data: dict):
+def decode_session_token(data: dict) -> dict:
     """
     This function reencodes a fragment of header which contains
     information about session token.
     """
-    data["body"]["object"]["target"]["container"] = json_reencode(
-        data["body"]["object"]["target"]["container"]["value"]
-    )
-    data["body"]["object"]["target"]["objects"] = [json_reencode(obj["value"]) for obj in data["body"]["object"]["target"]["objects"]]
+    target = data["body"]["object"]["target"]
+    target["container"] = json_reencode(target["container"]["value"])
+    target["objects"] = [json_reencode(obj["value"]) for obj in target["objects"]]
     return data
 
 
-def json_reencode(data: str):
+def json_reencode(data: str) -> str:
     """
     According to JSON protocol, binary data (Object/Container/Storage Group IDs, etc)
-    is converted to string via Base58 encoder. But we usually operate with Base64-encoded
-    format.
+    is converted to string via Base58 encoder. But we usually operate with Base64-encoded format.
     This function reencodes given Base58 string into the Base64 one.
     """
     return base58.b58encode(base64.b64decode(data)).decode("utf-8")
 
 
-def encode_for_json(data: str):
+def encode_for_json(data: str) -> str:
     """
     This function encodes binary data for sending them as protobuf
     structures.
@@ -131,7 +116,7 @@ def encode_for_json(data: str):
     return base64.b64encode(base58.b58decode(data)).decode("utf-8")
 
 
-def decode_common_fields(data: dict):
+def decode_common_fields(data: dict) -> dict:
     """
     Despite of type (simple/complex Object, Storage Group, etc) every Object
     header contains several common fields.