--- a
+++ b/pathaia/graphs/errors.py
@@ -0,0 +1,86 @@
+class Error(Exception):
+    """
+    Base of custom errors.
+    **********************
+    """
+
+    pass
+
+
+class InvalidNodeProps(Error):
+    """
+    Raise when trying to access unknown level.
+    *********************************************
+    """
+
+    pass
+
+
+class InvalidEdgeProps(Error):
+    """
+    Raise when trying to access unknown level.
+    *********************************************
+    """
+
+    pass
+
+
+class UndefinedParenthood(Error):
+    """
+    Raise when trying to access unknown level.
+    *********************************************
+    """
+
+    pass
+
+
+class UndefinedChildhood(Error):
+    """
+    Raise when trying to access unknown level.
+    *********************************************
+    """
+
+    pass
+
+
+class InvalidTree(Error):
+    """
+    Raise when parents and children do no match.
+    *********************************************
+    """
+
+
+class UnknownNodeProperty(Error):
+    """
+    Raise when trying to access unknown level.
+    *********************************************
+    """
+
+    pass
+
+
+class InvalidNodeId(Error):
+    """
+    Raise when trying to access unknown level.
+    *********************************************
+    """
+
+    pass
+
+
+class UnrelatedNode(Error):
+    """
+    Raise when trying to access unknown level.
+    *********************************************
+    """
+
+    pass
+
+
+class UnreachableAncestor(Error):
+    """
+    Raise when trying to access unknown level.
+    *********************************************
+    """
+
+    pass