diff --git a/saqc/__init__.py b/saqc/__init__.py
index 97de09a3958ccfba1254b72fb8840ad742d550f1..0c2bb6d4b68a2234e708e40fc693af29724a7826 100644
--- a/saqc/__init__.py
+++ b/saqc/__init__.py
@@ -3,7 +3,8 @@
 
 __version__ = "1.4"
 
-from saqc.core.core import SaQC
+# import order: from small to big
 from saqc.common import *
 from saqc.flagger import *
 from saqc.core.register import register
+from saqc.core.core import SaQC
diff --git a/saqc/common.py b/saqc/common.py
index 21010a0c678d5be5525e0e1599024bd4005682f0..9d4e3d504738717c230e30c9e445a04f2089ec72 100644
--- a/saqc/common.py
+++ b/saqc/common.py
@@ -1,8 +1,17 @@
 #!/usr/bin/env python
 
-from numpy import nan as _nan
+__all__ = [
+    "UNTOUCHED",
+    "UNFLAGGED",
+    "DOUBTFUL",
+    "BAD",
+    "GOOD",
+    "DOUBT",
+]
 
-UNTOUCHED = _nan
+import numpy as np
+
+UNTOUCHED = np.nan
 UNFLAGGED = 0
 DOUBTFUL = 25
 BAD = 255
@@ -10,3 +19,5 @@ BAD = 255
 # aliases
 GOOD = UNFLAGGED
 DOUBT = DOUBTFUL
+
+
diff --git a/saqc/core/__init__.py b/saqc/core/__init__.py
index 2f42342431e06979befbf39bbdf2e300b38ef2aa..097236acb6ecd8511ca716cb2b5206a8f00cdb80 100644
--- a/saqc/core/__init__.py
+++ b/saqc/core/__init__.py
@@ -1,5 +1,5 @@
 #! /usr/bin/env python
 # -*- coding: utf-8 -*-
 
-from saqc.core.core import SaQC, logger
 from saqc.core.register import register
+from saqc.core.core import SaQC, logger
diff --git a/saqc/flagger/__init__.py b/saqc/flagger/__init__.py
index e5a86852f8f1081755313450cc311398bda62957..bbf08253176273442cab40eaf62b886816403329 100644
--- a/saqc/flagger/__init__.py
+++ b/saqc/flagger/__init__.py
@@ -1,5 +1,5 @@
 #! /usr/bin/env python
 # -*- coding: utf-8 -*-
 
-from .flags import Flagger, initFlagsLike
 from .history import History
+from .flags import Flagger, initFlagsLike
diff --git a/saqc/funcs/changepoints.py b/saqc/funcs/changepoints.py
index b6e3f8aa435197e57e8b9f95ab6978d8b1126d90..f7234aa6f3a9e55cfabbdf03a21d008d3c27bbe4 100644
--- a/saqc/funcs/changepoints.py
+++ b/saqc/funcs/changepoints.py
@@ -11,6 +11,7 @@ from typing_extensions import Literal
 
 from dios import DictOfSeries
 
+from saqc.common import *
 from saqc.core.register import register
 from saqc.lib.tools import customRoller
 from saqc.flagger import Flagger
diff --git a/saqc/funcs/flagtools.py b/saqc/funcs/flagtools.py
index 364256e2926c49ef87f5c092b34a838144c5631a..40efed0f373d5866c6f5c2241e651b3ccca76dd5 100644
--- a/saqc/funcs/flagtools.py
+++ b/saqc/funcs/flagtools.py
@@ -8,11 +8,11 @@ import pandas as pd
 from dios import DictOfSeries
 
 from saqc.common import *
+from saqc.lib.types import *
 from saqc.core.register import register
 from saqc.flagger import Flagger
 
 
-
 @register(masking='field', module="flagtools")
 def clearFlags(data: DictOfSeries, field: ColumnName, flagger: Flagger, **kwargs) -> Tuple[DictOfSeries, Flagger]:
     flagger = flagger.clearFlags(field, **kwargs)
diff --git a/saqc/lib/types.py b/saqc/lib/types.py
index 650bfb0e779397b26e12b24710536b7ec1df0a3c..9a437a2a91f4574031b084f69d3e9ab6a6099d98 100644
--- a/saqc/lib/types.py
+++ b/saqc/lib/types.py
@@ -1,5 +1,17 @@
 #! /usr/bin/env python
 # -*- coding: utf-8 -*-
+__all__ = [
+    'T',
+    'ArrayLike',
+    'PandasLike',
+    'DiosLikeT',
+    'FuncReturnT',
+    'FreqString',
+    'ColumnName',
+    'IntegerWindow',
+    'TimestampColumnName',
+    'CurveFitter',
+]
 
 from typing import TypeVar, Union, NewType
 from typing_extensions import Protocol, Literal
@@ -7,13 +19,14 @@ from typing_extensions import Protocol, Literal
 import numpy as np
 import pandas as pd
 from dios import DictOfSeries
+from saqc import Flagger
 
 T = TypeVar("T")
 ArrayLike = TypeVar("ArrayLike", np.ndarray, pd.Series, pd.DataFrame)
 PandasLike = TypeVar("PandasLike", pd.Series, pd.DataFrame, DictOfSeries)
 DiosLikeT = Union[DictOfSeries, pd.DataFrame]
 
-FuncReturnT = [dios.DictOfSeries, Flagger]
+FuncReturnT = [DictOfSeries, Flagger]
 
 # we only support fixed length offsets
 FreqString = NewType("FreqString", Literal["D", "H", "T", "min", "S", "L", "ms", "U", "us", "N"])