diff --git a/Makefile b/Makefile
index e8a37ca..15675aa 100644
--- a/Makefile
+++ b/Makefile
@@ -20,7 +20,7 @@ black:
 	black lighttree tests setup.py
 
 mypy:
-	mypy lighttree
+	mypy lighttree --disallow-untyped-defs
 
 check: mypy black lint
 
diff --git a/lighttree/__init__.py b/lighttree/__init__.py
index 2077e58..578dd7c 100644
--- a/lighttree/__init__.py
+++ b/lighttree/__init__.py
@@ -1,4 +1,4 @@
 from .interactive import TreeBasedObj
-from .tree import Tree, Node
+from .tree import Tree, Node, Key, KeyedNode, KeyedTree
 
-__all__ = ["Tree", "Node", "TreeBasedObj"]
+__all__ = ["Tree", "Node", "TreeBasedObj", "Key", "KeyedNode", "KeyedTree"]
diff --git a/lighttree/implementations/json_tree.py b/lighttree/implementations/json_tree.py
index 326a96d..c8ac704 100644
--- a/lighttree/implementations/json_tree.py
+++ b/lighttree/implementations/json_tree.py
@@ -1,8 +1,11 @@
-from lighttree import Node, Tree
+from typing import Dict, Optional, Any, Union, List
+from lighttree import Node, Tree, Key
 
 
 class JsonTree(Tree):
-    def __init__(self, d=None, strict=True, path_separator="."):
+    def __init__(
+        self, d: Dict = None, strict: bool = True, path_separator: str = "."
+    ) -> None:
         """
         :param d:
         :param strict: if False, will convert tuples into arrays, else raise error
@@ -13,14 +16,16 @@ def __init__(self, d=None, strict=True, path_separator="."):
             self._fill(d, strict=strict, key=None)
 
     @staticmethod
-    def _concat(a, b):
+    def _concat(a: Any, b: Any) -> str:
         if not a and not b:
             return ""
         if not a:
             return str(b)
         return ".".join([str(a), str(b)])
 
-    def _fill(self, data, key, strict, path=None):
+    def _fill(
+        self, data: Any, key: Key, strict: bool, path: Optional[str] = None
+    ) -> None:
         if isinstance(data, list) or not strict and isinstance(data, tuple):
             k = self.insert_node(
                 Node(keyed=False), parent_id=path, key=key, by_path=True
@@ -50,10 +55,12 @@ def _fill(self, data, key, strict, path=None):
             return
         raise TypeError("Unsupported type %s" % type(data))
 
-    def to_dict(self):
+    def to_dict(self) -> Union[Dict, List, None]:
+        if self.root is None:
+            return None
         return self._to_dict(self.root)
 
-    def _to_dict(self, nid):
+    def _to_dict(self, nid: str) -> Any:
         _, n = self.get(nid)
         if not n.accept_children:
             return n.data
@@ -62,7 +69,7 @@ def _to_dict(self, nid):
             for sk, sn in self.children(n.identifier):
                 d[sk] = self._to_dict(sn.identifier)
             return d
-        d = []
+        l_ = []
         for _, sn in self.children(n.identifier):
-            d.append(self._to_dict(sn.identifier))
-        return d
+            l_.append(self._to_dict(sn.identifier))
+        return l_
diff --git a/lighttree/interactive.py b/lighttree/interactive.py
index e9d9018..9bb2f74 100644
--- a/lighttree/interactive.py
+++ b/lighttree/interactive.py
@@ -8,7 +8,7 @@
 from lighttree.tree import Tree
 
 
-def is_valid_attr_name(item) -> bool:
+def is_valid_attr_name(item: Any) -> bool:
     if not isinstance(item, str):
         return False
     if item.startswith("__"):
@@ -20,7 +20,7 @@ def is_valid_attr_name(item) -> bool:
     return True
 
 
-def _coerce_attr(attr) -> Union[str, None]:
+def _coerce_attr(attr: Any) -> Union[str, None]:
     if not len(attr):
         return None
     new_attr = unicodedata.normalize("NFD", attr).encode("ASCII", "ignore").decode()
@@ -55,7 +55,7 @@ class Obj(object):
     _STRING_KEY_CONSTRAINT = True
     _COERCE_ATTR = False
 
-    def __init__(self, **kwargs) -> None:
+    def __init__(self, **kwargs: Any) -> None:
         # will store non-valid names
         self.__d: Dict[str, Any] = dict()
         for k, v in kwargs.items():
@@ -69,14 +69,14 @@ def __init__(self, **kwargs) -> None:
                 )
             self[k] = v
 
-    def __getitem__(self, item):
+    def __getitem__(self, item: Any) -> Any:
         # when calling d[key]
         if is_valid_attr_name(item):
             return self.__getattribute__(item)
         else:
             return self.__d[item]
 
-    def __setitem__(self, key, value):
+    def __setitem__(self, key: Any, value: Any) -> None:
         # d[key] = value
         if not isinstance(key, str):
             if self._STRING_KEY_CONSTRAINT:
@@ -101,7 +101,7 @@ def __keys(self) -> List[Any]:
             k for k in self.__dict__.keys() if k not in ("_REPR_NAME", "_Obj__d")
         ]
 
-    def __contains__(self, item) -> bool:
+    def __contains__(self, item: Any) -> bool:
         return item in self.__keys()
 
     def __str__(self) -> str:
@@ -174,14 +174,14 @@ def _expand_attrs(self, depth: int) -> None:
                     child_node.identifier, root_path=child_root, depth=depth - 1
                 )
 
-    def __getattribute__(self, item):
+    def __getattribute__(self, item: Any) -> Any:
         # called by __getattribute__ will always refer to valid attribute item
         r = super(TreeBasedObj, self).__getattribute__(item)
         if isinstance(r, TreeBasedObj):
             r._expand_attrs(depth=1)
         return r
 
-    def __getitem__(self, item):
+    def __getitem__(self, item: Any) -> Any:
         if is_valid_attr_name(item):
             r = super(TreeBasedObj, self).__getattribute__(item)
         else:
@@ -190,7 +190,7 @@ def __getitem__(self, item):
             r._expand_attrs(depth=1)
         return r
 
-    def _show(self, *args, **kwargs) -> str:
+    def _show(self, *args: Any, **kwargs: Any) -> str:
         tree_repr = self._tree.show(*args, **kwargs)
         if self._root_path is None:
             return "<%s>\n%s" % (
@@ -204,7 +204,7 @@ def _show(self, *args, **kwargs) -> str:
             str(tree_repr),
         )
 
-    def __call__(self, *args, **kwargs) -> Tree:
+    def __call__(self, *args: Any, **kwargs: Any) -> Tree:
         return self._tree
 
     def __str__(self) -> str:
diff --git a/lighttree/node.py b/lighttree/node.py
index 28802f5..a2d516e 100644
--- a/lighttree/node.py
+++ b/lighttree/node.py
@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 import uuid
-from typing import Optional, Any, Tuple
+from typing import Optional, Any, Tuple, Union
 
 
 class Node(object):
@@ -12,7 +12,7 @@ def __init__(
         auto_uuid: bool = True,
         keyed: bool = True,
         accept_children: bool = True,
-        repr_: Optional[str] = None,
+        repr_: Optional[Union[str, float]] = None,
         data: Any = None,
     ) -> None:
         """
@@ -25,10 +25,10 @@ def __init__(
         self.identifier = identifier
         self.keyed = keyed
         self.accept_children = accept_children
-        self.repr = repr_
+        self.repr = str(repr_) if repr_ is not None else None
         self.data = data
 
-    def line_repr(self, depth: int, **kwargs) -> Tuple[str, str]:
+    def line_repr(self, depth: int, **kwargs: Any) -> Tuple[str, str]:
         """Control how node is displayed in tree representation.
         _
         ├── one                                           end
@@ -43,7 +43,7 @@ def line_repr(self, depth: int, **kwargs) -> Tuple[str, str]:
             return "{}", ""
         return "[]", ""
 
-    def __eq__(self, other) -> bool:
+    def __eq__(self, other: Any) -> bool:
         if not isinstance(other, self.__class__):
             return False
         return self.identifier == other.identifier
diff --git a/lighttree/py.typed b/lighttree/py.typed
new file mode 100644
index 0000000..e69de29
diff --git a/lighttree/tree.py b/lighttree/tree.py
index 4d19537..a7238ee 100644
--- a/lighttree/tree.py
+++ b/lighttree/tree.py
@@ -13,6 +13,7 @@
     Iterable,
     cast,
     Dict,
+    Any,
 )
 from collections import defaultdict
 from operator import itemgetter
@@ -718,7 +719,7 @@ def show(
         limit: Optional[int] = None,
         line_max_length: int = 60,
         key_delimiter: str = ": ",
-        **kwargs
+        **kwargs: Any
     ) -> str:
         """Return tree structure in hierarchy style.
 
@@ -832,13 +833,13 @@ def _line_prefix_repr(line_type: str, is_last_list: Tuple[bool, ...]) -> str:
         if not is_last_list:
             return ""
         dt_vertical_line, dt_line_box, dt_line_corner = STYLES[line_type]
-        leading = "".join(
+        leading: str = "".join(
             [
                 dt_vertical_line + " " * 3 if not is_last else " " * 4
                 for is_last in cast(Iterable[bool], is_last_list[0:-1])
             ]
         )
-        lasting = dt_line_corner if is_last_list[-1] else dt_line_box
+        lasting: str = dt_line_corner if is_last_list[-1] else dt_line_box
         return leading + lasting
 
     def merge(
diff --git a/lighttree/utils.py b/lighttree/utils.py
index 6fa004c..49e63d6 100644
--- a/lighttree/utils.py
+++ b/lighttree/utils.py
@@ -1,8 +1,9 @@
 #!/usr/bin/env python
 # -*- coding: utf-8 -*-
 
+from typing import Dict, Tuple
 
-STYLES = {
+STYLES: Dict[str, Tuple[str, str, str]] = {
     "ascii": ("|", "|-- ", "+-- "),
     "ascii-ex": ("\u2502", "\u251c\u2500\u2500 ", "\u2514\u2500\u2500 "),
     "ascii-exr": ("\u2502", "\u251c\u2500\u2500 ", "\u2570\u2500\u2500 "),
diff --git a/setup.cfg b/setup.cfg
index ba06156..abfb47b 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -2,4 +2,4 @@
 description-file = README.md
 
 [flake8]
-ignore=E501,W503
\ No newline at end of file
+ignore=E501,W503,W605
\ No newline at end of file
diff --git a/setup.py b/setup.py
index 0a4a48b..0825856 100644
--- a/setup.py
+++ b/setup.py
@@ -3,7 +3,7 @@
 
 from setuptools import setup
 
-__version__ = "1.1.2"
+__version__ = "1.1.3"
 
 develop_requires = [
     "pre-commit",
@@ -24,6 +24,9 @@
     author_email="leonardbinet@gmail.com",
     license="MIT",
     packages=["lighttree"],
+    package_data={
+        "lighttree": ["py.typed"],
+    },
     keywords=["tree", "interactive"],
     extras_require={"develop": develop_requires},
     tests_require=develop_requires,
diff --git a/tests/test_tree.py b/tests/test_tree.py
index b4183dc..f5c54e1 100644
--- a/tests/test_tree.py
+++ b/tests/test_tree.py
@@ -536,23 +536,27 @@ def test_show(self):
 
     def test_prefix_repr(self):
         self.assertEqual(
-            Tree._line_prefix_repr(line_type="ascii-ex", is_last_list=[]), ""
+            Tree._line_prefix_repr(
+                line_type="ascii-ex",
+                is_last_list=(),
+            ),
+            "",
         )
         self.assertEqual(
-            Tree._line_prefix_repr(line_type="ascii-ex", is_last_list=[True]), "└── "
+            Tree._line_prefix_repr(line_type="ascii-ex", is_last_list=(True,)), "└── "
         )
         self.assertEqual(
-            Tree._line_prefix_repr(line_type="ascii-ex", is_last_list=[False]), "├── "
+            Tree._line_prefix_repr(line_type="ascii-ex", is_last_list=(False,)), "├── "
         )
         self.assertEqual(
             Tree._line_prefix_repr(
-                line_type="ascii-ex", is_last_list=[True, False, True]
+                line_type="ascii-ex", is_last_list=(True, False, True)
             ),
             "    │   └── ",
         )
         self.assertEqual(
             Tree._line_prefix_repr(
-                line_type="ascii-ex", is_last_list=[False, False, False]
+                line_type="ascii-ex", is_last_list=(False, False, False)
             ),
             "│   │   ├── ",
         )