diff --git a/API_CHANGELOG.md b/API_CHANGELOG.md
index 0411b0e7f7..66306fd583 100644
--- a/API_CHANGELOG.md
+++ b/API_CHANGELOG.md
@@ -46,6 +46,11 @@ included in this changelog.
 
 ### Modifications
 
+- All APIs: errors during a request are now indicated with a more useful HTTP
+  status code than 200: errors related to the request, input data and the client
+  will result in status 400, permission errors in status 403, unavailable
+  resources in status 404 and internal server errors in status 500.
+
 - `POST|GET /{project_id}/node/list`:
   Offers a new optional parameter
   "ordering", which can be used to order the result set of nodes. The values
diff --git a/CHANGELOG.md b/CHANGELOG.md
index fb8f7537b2..6e03787ee8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -32,6 +32,11 @@
   the tracing tool is now enabled for new users, because it seems in many setups
   users want to have this enabled by default.
 
+- Back-end errors result now in actual HTTP error status codes. Third-party
+  clients need possibly some adjustments to handle API errors. In case of an
+  error, status 400 is returned if an input data or parameter problem, 401 for
+  permission problems and 500 otherwise.
+
 ### Features and enhancements
 
 Node filters:
diff --git a/UPDATE.md b/UPDATE.md
index 17af2a385d..969a79c529 100644
--- a/UPDATE.md
+++ b/UPDATE.md
@@ -9,6 +9,11 @@ and other administration related changes are listed in order.
   PostGIS first and run `ALTER EXTENSION postgis UPDATE;` in every database. For
   docker-compose setups this database update is performed automatically.
 
+- Back-end errors result now in actual HTTP error status codes. Third-party
+  clients need possibly some adjustments to handle API errors. In case of an
+  error, status 400 is returned if an input data or parameter problem, 401 for
+  permission problems and 500 otherwise.
+
 ## 2019.06.20
 
 - A virtualenv update is required.
diff --git a/django/applications/catmaid/control/authentication.py b/django/applications/catmaid/control/authentication.py
index a27acd1074..fbc5fe7e77 100644
--- a/django/applications/catmaid/control/authentication.py
+++ b/django/applications/catmaid/control/authentication.py
@@ -28,21 +28,22 @@
 from rest_framework.authtoken import views as auth_views
 from rest_framework.authtoken.serializers import AuthTokenSerializer
 
+from catmaid.error import ClientError
 from catmaid.models import Project, UserRole, ClassInstance, \
         ClassInstanceClassInstance
 
 
-class PermissionError(Exception):
+class PermissionError(ClientError):
     """Indicates the lack of permissions for a particular action."""
-    pass
+    status_code = 403
 
 
-class InvalidLoginError(Exception):
+class InvalidLoginError(ClientError):
     """Indicates an unsuccessful login."""
-    pass
+    status_code = 400
 
 
-class InactiveLoginError(Exception):
+class InactiveLoginError(ClientError):
     """Indicates some sort of configuration error"""
     def __init__(self, message, meta=None):
         super().__init__(message)
@@ -120,6 +121,7 @@ def user_context_response(user, additional_fields=None) -> JsonResponse:
         'userid': user.id,
         'username': user.username,
         'is_superuser': user.is_superuser,
+        'is_authenticated': user != get_anonymous_user(),
         'userprofile': user.userprofile.as_dict(),
         'permissions': tuple(user.get_all_permissions()),
         'domain': list(user_domain(cursor, user.id))
@@ -386,7 +388,7 @@ def can_edit_class_instance_or_fail(user, ci_id, name='object') -> bool:
                     locked_by_other[0].user_id):
                 return True
 
-            raise Exception('User %s with id #%s cannot edit %s #%s' % \
+            raise PermissionError('User %s with id #%s cannot edit %s #%s' % \
                 (user.username, user.id, name, ci_id))
         # The class instance is locked by user or not locked at all
         return True
@@ -419,7 +421,7 @@ def can_edit_or_fail(user, ob_id:int, table_name) -> bool:
             if user_can_edit(cursor, user.id, owner_id):
                 return True
 
-        raise Exception('User %s with id #%s cannot edit object #%s (from user #%s) from table %s' % (user.username, user.id, ob_id, rows[0][0], table_name))
+        raise PermissionError('User %s with id #%s cannot edit object #%s (from user #%s) from table %s' % (user.username, user.id, ob_id, rows[0][0], table_name))
     raise ObjectDoesNotExist('Object #%s not found in table %s' % (ob_id, table_name))
 
 
@@ -448,7 +450,7 @@ def can_edit_all_or_fail(user, ob_ids, table_name) -> bool:
         if set(row[0] for row in rows).issubset(user_domain(cursor, user.id)):
             return True
 
-        raise Exception('User %s cannot edit all of the %s unique objects from table %s' % (user.username, len(ob_ids), table_name))
+        raise PermissionError('User %s cannot edit all of the %s unique objects from table %s' % (user.username, len(ob_ids), table_name))
     raise ObjectDoesNotExist('One or more of the %s unique objects were not found in table %s' % (len(ob_ids), table_name))
 
 def user_can_edit(cursor, user_id, other_user_id) -> bool:
diff --git a/django/applications/catmaid/control/pointcloud.py b/django/applications/catmaid/control/pointcloud.py
index a8fc6b52fb..4c03fa18ff 100644
--- a/django/applications/catmaid/control/pointcloud.py
+++ b/django/applications/catmaid/control/pointcloud.py
@@ -17,7 +17,7 @@
 from rest_framework.decorators import api_view
 
 from catmaid.control.authentication import (requires_user_role,
-        can_edit_or_fail, check_user_role)
+        can_edit_or_fail, check_user_role, PermissionError)
 from catmaid.control.common import (insert_into_log, get_class_to_id_map,
         get_relation_to_id_map, _create_relation, get_request_bool,
         get_request_list)
diff --git a/django/applications/catmaid/control/similarity.py b/django/applications/catmaid/control/similarity.py
index d3e4999e9c..7165dbabbe 100644
--- a/django/applications/catmaid/control/similarity.py
+++ b/django/applications/catmaid/control/similarity.py
@@ -20,7 +20,7 @@
 
 from catmaid.consumers import msg_user
 from catmaid.control.authentication import (requires_user_role,
-        can_edit_or_fail, check_user_role)
+        can_edit_or_fail, check_user_role, PermissionError)
 from catmaid.control.common import (insert_into_log, get_class_to_id_map,
         get_relation_to_id_map, _create_relation, get_request_bool,
         get_request_list)
diff --git a/django/applications/catmaid/control/skeleton.py b/django/applications/catmaid/control/skeleton.py
index f8fbc8fc7f..def8b99d9a 100644
--- a/django/applications/catmaid/control/skeleton.py
+++ b/django/applications/catmaid/control/skeleton.py
@@ -144,7 +144,7 @@ def _open_leaves(project_id, skeleton_id, tnid=None):
                 tnid = node_id
 
     if tnid not in tree:
-        raise Exception("Could not find %s in skeleton %s" % (tnid, int(skeleton_id)))
+        raise ValueError("Could not find %s in skeleton %s" % (tnid, int(skeleton_id)))
 
     reroot(tree, tnid)
     distances = edge_count_to_root(tree, root_node=tnid)
@@ -301,7 +301,7 @@ def _find_labels(project_id, skeleton_id, label_regex, tnid=None,
                 props['tags'] = [row[5]]
 
     if tnid not in tree:
-        raise Exception("Could not find %s in skeleton %s" % (tnid, int(skeleton_id)))
+        raise ValueError("Could not find %s in skeleton %s" % (tnid, int(skeleton_id)))
 
     reroot(tree, tnid)
     distances = edge_count_to_root(tree, root_node=tnid)
@@ -370,7 +370,7 @@ def within_spatial_distance(request:HttpRequest, project_id=None) -> JsonRespons
     project_id = int(project_id)
     tnid = request.POST.get('treenode_id', None)
     if not tnid:
-        raise Exception("Need a treenode!")
+        raise ValueError("Need a treenode!")
     tnid = int(tnid)
     distance = int(request.POST.get('distance', 0))
     if 0 == distance:
@@ -661,7 +661,7 @@ def _get_neuronname_from_skeletonid( project_id, skeleton_id ):
         return {'neuronname': qs[0].class_instance_b.name,
             'neuronid': qs[0].class_instance_b.id }
     except IndexError:
-        raise Exception("Couldn't find a neuron linking to a skeleton with " \
+        raise ValueError("Couldn't find a neuron linking to a skeleton with " \
                 "ID %s" % skeleton_id)
 
 @requires_user_role([UserRole.Annotate, UserRole.Browse])
@@ -1173,7 +1173,7 @@ def split_skeleton(request:HttpRequest, project_id=None) -> JsonResponse:
     if not check_annotations_on_split(project_id, skeleton_id,
             frozenset(upstream_annotation_map.keys()),
             frozenset(downstream_annotation_map.keys())):
-        raise Exception("Annotation distribution is not valid for splitting. " \
+        raise ValueError("Annotation distribution is not valid for splitting. " \
           "One part has to keep the whole set of annotations!")
 
     skeleton = ClassInstance.objects.select_related('user').get(pk=skeleton_id)
@@ -1485,12 +1485,12 @@ def skeleton_ancestry(request:HttpRequest, project_id=None) -> JsonResponse:
     # prefetch_related when we upgrade to Django 1.4 or above
     skeleton_id = int(request.POST.get('skeleton_id', None))
     if skeleton_id is None:
-        raise Exception('A skeleton id has not been provided!')
+        raise ValueError('A skeleton id has not been provided!')
 
     relation_map = get_relation_to_id_map(project_id)
     for rel in ['model_of', 'part_of']:
         if rel not in relation_map:
-            raise Exception(' => "Failed to find the required relation %s' % rel)
+            raise ValueError(' => "Failed to find the required relation %s' % rel)
 
     response_on_error = ''
     try:
@@ -1502,9 +1502,9 @@ def skeleton_ancestry(request:HttpRequest, project_id=None) -> JsonResponse:
             'class_instance_b__name')
         neuron_count = neuron_rows.count()
         if neuron_count == 0:
-            raise Exception('No neuron was found that the skeleton %s models' % skeleton_id)
+            raise ValueError('No neuron was found that the skeleton %s models' % skeleton_id)
         elif neuron_count > 1:
-            raise Exception('More than one neuron was found that the skeleton %s models' % skeleton_id)
+            raise ValueError('More than one neuron was found that the skeleton %s models' % skeleton_id)
 
         parent_neuron = neuron_rows[0]
         ancestry = []
@@ -1531,7 +1531,7 @@ def skeleton_ancestry(request:HttpRequest, project_id=None) -> JsonResponse:
             if parent_count == 0:
                 break  # We've reached the top of the hierarchy.
             elif parent_count > 1:
-                raise Exception('More than one class_instance was found that the class_instance %s is part_of.' % current_ci)
+                raise ValueError('More than one class_instance was found that the class_instance %s is part_of.' % current_ci)
             else:
                 parent = parents[0]
                 ancestry.append({
@@ -2074,14 +2074,14 @@ def reroot_skeleton(request:HttpRequest, project_id=None) -> JsonResponse:
         # Else, already root
         return JsonResponse({'error': 'Node #%s is already root!' % treenode_id})
     except Exception as e:
-        raise Exception(response_on_error + ':' + str(e))
+        raise ValueError(response_on_error + ':' + str(e))
 
 
 def _reroot_skeleton(treenode_id, project_id):
     """ Returns the treenode instance that is now root,
     or False if the treenode was root already. """
     if treenode_id is None:
-        raise Exception('A treenode id has not been provided!')
+        raise ValueError('A treenode id has not been provided!')
 
     response_on_error = ''
     try:
@@ -2092,7 +2092,7 @@ def _reroot_skeleton(treenode_id, project_id):
         n_samplers = Sampler.objects.filter(skeleton=rootnode.skeleton).count()
         response_on_error = 'Neuron is used in a sampler, can\'t reroot'
         if n_samplers > 0:
-            raise Exception(f'Skeleton {rootnode.skeleton_id} is used in {n_samplers} sampler(s)')
+            raise ValueError(f'Skeleton {rootnode.skeleton_id} is used in {n_samplers} sampler(s)')
 
         # Obtain the treenode from the response
         first_parent = rootnode.parent_id
@@ -2145,7 +2145,7 @@ def _reroot_skeleton(treenode_id, project_id):
         return rootnode
 
     except Exception as e:
-        raise Exception(f'{response_on_error}: {e}')
+        raise ValueError(f'{response_on_error}: {e}')
 
 
 def _root_as_parent(oid):
@@ -2199,7 +2199,7 @@ def join_skeleton(request:HttpRequest, project_id=None) -> JsonResponse:
         })
 
     except Exception as e:
-        raise Exception(response_on_error + ':' + str(e))
+        raise ValueError(response_on_error + ':' + str(e))
 
 
 def make_annotation_map(annotation_vs_user_id, neuron_id, cursor=None) -> Dict:
@@ -2253,7 +2253,7 @@ def _join_skeleton(user, from_treenode_id, to_treenode_id, project_id,
     annotation that references the merged in skeleton using its name.
     """
     if from_treenode_id is None or to_treenode_id is None:
-        raise Exception('Missing arguments to _join_skeleton')
+        raise ValueError('Missing arguments to _join_skeleton')
 
     response_on_error = ''
     try:
@@ -2263,12 +2263,12 @@ def _join_skeleton(user, from_treenode_id, to_treenode_id, project_id,
         try:
             from_treenode = Treenode.objects.get(pk=from_treenode_id)
         except Treenode.DoesNotExist:
-            raise Exception("Could not find a skeleton for treenode #%s" % from_treenode_id)
+            raise ValueError("Could not find a skeleton for treenode #%s" % from_treenode_id)
 
         try:
             to_treenode = Treenode.objects.get(pk=to_treenode_id)
         except Treenode.DoesNotExist:
-            raise Exception("Could not find a skeleton for treenode #%s" % to_treenode_id)
+            raise ValueError("Could not find a skeleton for treenode #%s" % to_treenode_id)
 
         from_skid = from_treenode.skeleton_id
         from_neuron = _get_neuronname_from_skeletonid( project_id, from_skid )
@@ -2277,7 +2277,7 @@ def _join_skeleton(user, from_treenode_id, to_treenode_id, project_id,
         to_neuron = _get_neuronname_from_skeletonid( project_id, to_skid )
 
         if from_skid == to_skid:
-            raise Exception('Cannot join treenodes of the same skeleton, this would introduce a loop.')
+            raise ValueError('Cannot join treenodes of the same skeleton, this would introduce a loop.')
 
         # Make sure the user has permissions to edit both neurons
         can_edit_class_instance_or_fail(
@@ -2342,7 +2342,7 @@ def merge_into_annotation_map(source, skid, target):
             if not check_annotations_on_join(project_id, user,
                     from_neuron['neuronid'], to_neuron['neuronid'],
                     frozenset(annotation_map.keys())):
-                raise Exception("Annotation distribution is not valid for joining. " \
+                raise ValueError("Annotation distribution is not valid for joining. " \
                 "Annotations for which you don't have permissions have to be kept!")
 
         # Find oldest creation_time and edition_time
@@ -2436,7 +2436,7 @@ def merge_into_annotation_map(source, skid, target):
         return response
 
     except Exception as e:
-        raise Exception(response_on_error + ':' + str(e))
+        raise ValueError(response_on_error + ':' + str(e))
 
 
 def _update_samplers_in_merge(project_id, user_id, win_skeleton_id, lose_skeleton_id,
@@ -2996,7 +2996,7 @@ def relate_neuron_to_skeleton(neuron, skeleton):
     # treenodes.
     root = find_root(arborescence)
     if root is None:
-        raise Exception('No root, provided graph is malformed!')
+        raise ValueError('No root, provided graph is malformed!')
 
     # Bulk create the required number of treenodes. This must be done in two
     # steps because treenode IDs are not known.
diff --git a/django/applications/catmaid/control/textlabel.py b/django/applications/catmaid/control/textlabel.py
index 59415d265b..db9639616a 100644
--- a/django/applications/catmaid/control/textlabel.py
+++ b/django/applications/catmaid/control/textlabel.py
@@ -51,7 +51,7 @@ def update_textlabel(request:HttpRequest, project_id=None) -> HttpResponse:
         return HttpResponse(' ')
 
     except Exception as e:
-        raise Exception(response_on_error + ':' + str(e))
+        raise ValueError(response_on_error + ':' + str(e))
 
 
 @requires_user_role(UserRole.Annotate)
diff --git a/django/applications/catmaid/control/transaction.py b/django/applications/catmaid/control/transaction.py
index 1976bf8ed9..802723a8b5 100644
--- a/django/applications/catmaid/control/transaction.py
+++ b/django/applications/catmaid/control/transaction.py
@@ -3,6 +3,7 @@
 from typing import Dict
 from django.db import connection
 
+from catmaid.error import ClientError
 from catmaid.control.authentication import requires_user_role
 from catmaid.models import UserRole
 
@@ -11,7 +12,7 @@
 from rest_framework.response import Response
 
 
-class LocationLookupError(Exception):
+class LocationLookupError(ClientError):
     pass
 
 
diff --git a/django/applications/catmaid/control/treenode.py b/django/applications/catmaid/control/treenode.py
index 88e412d3ed..bd32147de0 100644
--- a/django/applications/catmaid/control/treenode.py
+++ b/django/applications/catmaid/control/treenode.py
@@ -422,7 +422,7 @@ def relate_neuron_to_skeleton(neuron, skeleton):
 
     except Exception as e:
         import traceback
-        raise Exception("%s: %s %s" % (response_on_error, str(e),
+        raise ValueError("%s: %s %s" % (response_on_error, str(e),
                                        str(traceback.format_exc())))
 
 
@@ -441,7 +441,7 @@ def update_parent(request:HttpRequest, project_id=None, treenode_id=None) -> Jso
     parent = get_object_or_404(Treenode, pk=parent_id, project_id=project_id)
 
     if child.skeleton_id != parent.skeleton_id:
-        raise Exception("Child node %s is in skeleton %s but parent node %s is in skeleton %s!", \
+        raise ValueError("Child node %s is in skeleton %s but parent node %s is in skeleton %s!", \
                         treenode_id, child.skeleton_id, parent_id, parent.skeleton_id)
 
     child.parent_id = parent_id
@@ -531,7 +531,7 @@ def update_radius(request:HttpRequest, project_id=None, treenode_id=None) -> Jso
     treenode_id = int(treenode_id)
     radius = float(request.POST.get('radius', -1))
     if math.isnan(radius):
-        raise Exception("Radius '%s' is not a number!" % request.POST.get('radius'))
+        raise ValueError("Radius '%s' is not a number!" % request.POST.get('radius'))
     option = int(request.POST.get('option', 0))
     cursor = connection.cursor()
     # Make sure the back-end is in the expected state
@@ -697,7 +697,7 @@ def delete_treenode(request:HttpRequest, project_id=None) -> JsonResponse:
             if n_children > 0:
                 # TODO yes you can, the new root is the first of the children,
                 # and other children become independent skeletons
-                raise Exception("You can't delete the root node when it "
+                raise ValueError("You can't delete the root node when it "
                                 "has children.")
             # Get the neuron before the skeleton is deleted. It can't be
             # accessed otherwise anymore.
@@ -768,7 +768,7 @@ def delete_treenode(request:HttpRequest, project_id=None) -> JsonResponse:
         })
 
     except Exception as e:
-        raise Exception(response_on_error + ': ' + str(e))
+        raise ValueError(response_on_error + ': ' + str(e))
 
 def _compact_detail_list(project_id, treenode_ids=None, label_ids=None,
         label_names=None, skeleton_ids=None):
@@ -1020,7 +1020,7 @@ def find_children(request:HttpRequest, project_id=None, treenode_id=None) -> Jso
         children = [[row] for row in cursor.fetchall()]
         return JsonResponse(children, safe=False)
     except Exception as e:
-        raise Exception('Could not obtain next branch node or leaf: ' + str(e))
+        raise ValueError('Could not obtain next branch node or leaf: ' + str(e))
 
 
 @api_view(['POST'])
@@ -1176,7 +1176,7 @@ def _find_first_interesting_node(sequence):
     Otherwise return the last node.
     """
     if not sequence:
-        raise Exception('No nodes ahead!')
+        raise ValueError('No nodes ahead!')
 
     if 1 == len(sequence):
         return sequence[0]
@@ -1201,7 +1201,7 @@ def _find_first_interesting_node(sequence):
             if props[1] < 5 or props[2] or props[3]:
                 return node_id
         else:
-            raise Exception('Nodes of this skeleton changed while inspecting them.')
+            raise ValueError('Nodes of this skeleton changed while inspecting them.')
 
     return sequence[-1]
 
@@ -1231,7 +1231,7 @@ def find_previous_branchnode_or_root(request:HttpRequest, project_id=None, treen
 
         return JsonResponse(_fetch_location(project_id, tnid), safe=False)
     except Exception as e:
-        raise Exception('Could not obtain previous branch node or root:' + str(e))
+        raise ValueError('Could not obtain previous branch node or root:' + str(e))
 
 
 @requires_user_role([UserRole.Annotate, UserRole.Browse])
@@ -1275,4 +1275,4 @@ def find_next_branchnode_or_end(request:HttpRequest, project_id=None, treenode_i
         branches = [[node_locations[node_id] for node_id in branch] for branch in branches]
         return JsonResponse(branches, safe=False)
     except Exception as e:
-        raise Exception('Could not obtain next branch node or leaf: ' + str(e))
+        raise ValueError('Could not obtain next branch node or leaf: ' + str(e))
diff --git a/django/applications/catmaid/control/user.py b/django/applications/catmaid/control/user.py
index dc6802fa9d..088c45d359 100644
--- a/django/applications/catmaid/control/user.py
+++ b/django/applications/catmaid/control/user.py
@@ -12,7 +12,7 @@
 from django.contrib.auth.models import User
 import django.contrib.auth.views as django_auth_views
 
-from catmaid.control.authentication import access_check
+from catmaid.control.authentication import (access_check, PermissionError)
 from catmaid.control.common import get_request_bool
 
 
diff --git a/django/applications/catmaid/error.py b/django/applications/catmaid/error.py
new file mode 100644
index 0000000000..9e4c7380c7
--- /dev/null
+++ b/django/applications/catmaid/error.py
@@ -0,0 +1,8 @@
+# -*- coding: utf-8 -*-
+
+
+class ClientError(ValueError):
+    """Client errors are the result of bad values or requests by the client. In
+    the general case this will result in a status 400 error.
+    """
+    status_code = 400
diff --git a/django/applications/catmaid/middleware.py b/django/applications/catmaid/middleware.py
index d2bf2c9a3f..d387c1d619 100644
--- a/django/applications/catmaid/middleware.py
+++ b/django/applications/catmaid/middleware.py
@@ -7,12 +7,15 @@
 from traceback import format_exc
 from datetime import datetime
 
-from django.http import JsonResponse
+from django.http import JsonResponse, Http404
 from django.conf import settings
 
 from guardian.utils import get_anonymous_user
 
 from rest_framework.authentication import TokenAuthentication
+from rest_framework.exceptions import APIException
+
+from catmaid.error import ClientError
 
 from io import StringIO
 
@@ -104,7 +107,21 @@ def process_exception(self, request, exception):
             (exc_type, exc_info, tb) = sys.exc_info()
             response['info'] = str(exc_info)
             response['traceback'] = ''.join(traceback.format_tb(tb))
-        return JsonResponse(response)
+
+        # Some CATMAID errors have a more detailed status code
+        if isinstance(exception, ClientError):
+            status = exception.status_code
+        elif isinstance(exception, Http404):
+            status = 404
+        elif isinstance(exception, APIException):
+            status = exception.status_code
+        elif isinstance(exception, ValueError):
+            # Value errors are assumed to be problems with the request/client.
+            status = 400
+        else:
+            status = 500
+
+        return JsonResponse(response, status=status, safe=False)
 
 
 class BasicModelMapMiddleware(object):
diff --git a/django/applications/catmaid/state.py b/django/applications/catmaid/state.py
index 65033de6ac..9c2b253905 100644
--- a/django/applications/catmaid/state.py
+++ b/django/applications/catmaid/state.py
@@ -7,8 +7,10 @@
 
 from django.db import connection
 
+from catmaid.error import ClientError
 
-class StateMatchingError(Exception):
+
+class StateMatchingError(ClientError):
     """Indicates that a state check wasn't successful"""
     def __init__(self, message, state):
         super().__init__(message)
diff --git a/django/applications/catmaid/static/js/CATMAID.js b/django/applications/catmaid/static/js/CATMAID.js
index 31361071a8..ca30247974 100644
--- a/django/applications/catmaid/static/js/CATMAID.js
+++ b/django/applications/catmaid/static/js/CATMAID.js
@@ -184,49 +184,6 @@
    */
   CATMAID.warn = CATMAID.msg.bind(window, "Warning");
 
-  /**
-   * Creates a generic JSON response handler that complains when the response
-   * status is different from 200 or a JSON error is set.
-   *
-   * @param success Called on success
-   * @param error Called on error
-   * @param silent No error dialogs are shown, if true
-   */
-  CATMAID.jsonResponseHandler = function(success, error, silent)
-  {
-    return function(status, text, xml) {
-      if (status >= 200 && status <= 204 &&
-          (typeof text === 'string' || text instanceof String)) {
-        // `text` may be empty for no content responses.
-        var json = text.length ? JSON.parse(text) : {};
-        if (json.error) {
-          // Call error handler, if any, and force silence if it returned true.
-          if (CATMAID.tools.isFn(error)) {
-            silent = error(json) || silent;
-          }
-          if (!silent) {
-            CATMAID.error(json.error, json.detail);
-          }
-        } else {
-          CATMAID.tools.callIfFn(success, json);
-        }
-      } else {
-        var e = {
-          error: "An error occured",
-          detail: "The server returned an unexpected status: " + status,
-          status: status
-        };
-        // Call error handler, if any, and force silence if it returned true.
-        if (CATMAID.tools.isFn(error)) {
-          silent = error(e) || silent;
-        }
-        if (!silent) {
-          CATMAID.error(e.msg, e.detail);
-        }
-      }
-    };
-  };
-
   /**
    * Convenience function to show an error dialog.
    */
diff --git a/django/applications/catmaid/static/js/widgets/compartment_graph_widget.js b/django/applications/catmaid/static/js/widgets/compartment_graph_widget.js
index 5a21a9a659..8a78e22a8f 100644
--- a/django/applications/catmaid/static/js/widgets/compartment_graph_widget.js
+++ b/django/applications/catmaid/static/js/widgets/compartment_graph_widget.js
@@ -2271,28 +2271,31 @@
         accum = $.extend({}, s.split_partners); // TODO unused?
 
     var grow = function(skids, n_circles, callback) {
-          requestQueue.register(CATMAID.makeURL(project.id + "/graph/circlesofhell"),
-              "POST",
-              {skeleton_ids: skids,
-               n_circles: n_circles,
-               min_pre: p.min_upstream,
-               min_post: p.min_downstream},
-              CATMAID.jsonResponseHandler(function(json) {
-                if (p.filter_regex !== '') {
-                  requestQueue.register(CATMAID.makeURL(project.id + "/annotations/forskeletons"),
-                      "POST",
-                      {skeleton_ids: json[0]},
-                      CATMAID.jsonResponseHandler(function (json) {
-                        var filterRegex = new RegExp(p.filter_regex, 'i');
-                        var filteredNeighbors = Object.keys(json.skeletons).filter(function (skid) {
-                          return json.skeletons[skid].some(function (a) {
-                            return filterRegex.test(json.annotations[a.id]);
-                          });
-                        });
-                        callback(skids.concat(filteredNeighbors));
-                      }));
-                } else callback(skids.concat(json[0]));
-              }));
+        CATMAID.fetch(project.id + "/graph/circlesofhell", "POST", {
+            skeleton_ids: skids,
+            n_circles: n_circles,
+            min_pre: p.min_upstream,
+            min_post: p.min_downstream,
+          })
+          .then(json => {
+            if (p.filter_regex !== '') {
+              return CATMAID.fetch(project.id + "/annotations/forskeletons", "POST", {
+                  skeleton_ids: json[0],
+                })
+                .then(annotations => {
+                  var filterRegex = new RegExp(p.filter_regex, 'i');
+                  var filteredNeighbors = Object.keys(annotations.skeletons).filter(function (skid) {
+                    return annotations.skeletons[skid].some(function (a) {
+                      return filterRegex.test(annotations.annotations[a.id]);
+                    });
+                  });
+                  callback(skids.concat(filteredNeighbors));
+                });
+            } else {
+              callback(skids.concat(json[0]));
+            }
+          })
+          .catch(CATMAID.handleError);
         },
         append = (function(skids) {
           var color = new THREE.Color().setHex(0xffae56),
diff --git a/django/applications/catmaid/static/js/widgets/overlay.js b/django/applications/catmaid/static/js/widgets/overlay.js
index fdc6da4403..3fdfd0fa3c 100644
--- a/django/applications/catmaid/static/js/widgets/overlay.js
+++ b/django/applications/catmaid/static/js/widgets/overlay.js
@@ -4062,7 +4062,7 @@ var SkeletonAnnotations = {};
           }
 
           return Promise.all(requests);
-        })
+        }, e => true /* Tell submitter we handle error */)
         .then(function(responses) {
           // Bail if the overlay was destroyed or suspended before this callback.
           if (self.suspended) {
@@ -4143,7 +4143,8 @@ var SkeletonAnnotations = {};
 
       // Return a proper promise to the caller (i.e. no submitter instance).
       return work.promise();
-    });
+    })
+    .catch(CATMAID.handleError);
   };
 
   CATMAID.TracingOverlay.prototype.createSubViewNodeListFromCache = function(params) {
diff --git a/django/applications/catmaid/static/libs/catmaid/CATMAID.js b/django/applications/catmaid/static/libs/catmaid/CATMAID.js
index c3796d3df0..c4f140f1dc 100644
--- a/django/applications/catmaid/static/libs/catmaid/CATMAID.js
+++ b/django/applications/catmaid/static/libs/catmaid/CATMAID.js
@@ -317,15 +317,8 @@ var requestQueue = new CATMAID.RequestQueue();
       return text;
     } else if (additionalStatusCodes && additionalStatusCodes.indexOf(status) > -1) {
       return text;
-    } else if (status === 502) { // Bad Gateway
-      var error = new CATMAID.NetworkAccessError("CATMAID server unreachable",
-          "Please wait or try to reload");
-      error.statusCode = status;
-      throw error;
     } else {
-      var error = new CATMAID.Error("The server returned an unexpected status: " + status);
-      error.statusCode = status;
-      throw error;
+      throw new CATMAID.Error("The server returned an unexpected status: " + status);
     }
   };
 
@@ -338,19 +331,14 @@ var requestQueue = new CATMAID.RequestQueue();
   CATMAID.validateJsonResponse = function(status, text, xml, additionalStatusCodes) {
     var response = CATMAID.validateResponse(status, text, xml, undefined, additionalStatusCodes);
     // `text` may be empty for no content responses.
-    var json = text.length ? JSON.parse(text) : {};
-    if (json.error) {
-      var error = CATMAID.parseErrorResponse(json);
-      throw error;
-    } else {
-      return json;
-    }
+    return text.length ? JSON.parse(text) : {};
   };
 
   /**
    * Translate an error response into the appropriate front-end type.
    */
-  CATMAID.parseErrorResponse = function(error) {
+  CATMAID.parseErrorResponse = function(error, statusCode = undefined) {
+    error = error | {};
     if ('ValueError' === error.type) {
       return new CATMAID.ValueError(error.error, error.detail);
     } else if ('StateMatchingError' === error.type) {
@@ -365,6 +353,10 @@ var requestQueue = new CATMAID.RequestQueue();
       return new CATMAID.InactiveLoginError(error.error, error.detail, error.meta);
     } else if ('ReplacedRequestError' === error.type) {
       return new CATMAID.ReplacedRequestError(error.error, error.detail);
+    } else if (statusCode === 404) {
+      return new CATMAID.MissingResourceError(error.error, error.detail);
+    } else if (statusCode === 403) {
+      return new CATMAID.PermissionError("Insufficient permissions", error);
     } else {
       return new CATMAID.Error("Unsuccessful request: " + error.error,
           error.detail, error.type);
@@ -450,6 +442,22 @@ var requestQueue = new CATMAID.RequestQueue();
         // this wasn't an asynchronously called function. But since this is the
         // case, we have to call reject() explicitly.
         try {
+          // Handle client and server errors
+          if (status >= 400 && status < 600) {
+            if (status === 502) { // Bad Gateway
+              var error = new CATMAID.NetworkAccessError("CATMAID server unreachable",
+                  "Please wait or try to reload");
+              throw error;
+            }
+            let errorDetails;
+            try {
+              errorDetails = JSON.parse(text);
+            } catch (e) {
+              errorDetails = null;
+            }
+            throw CATMAID.parseErrorResponse(errorDetails, status);
+          }
+
           if (raw) {
             var response = CATMAID.validateResponse(status, text, xml,
                 responseType, supportedStatus);
diff --git a/django/applications/catmaid/static/libs/catmaid/datastores.js b/django/applications/catmaid/static/libs/catmaid/datastores.js
index 4de9d6912b..490c66d235 100644
--- a/django/applications/catmaid/static/libs/catmaid/datastores.js
+++ b/django/applications/catmaid/static/libs/catmaid/datastores.js
@@ -44,59 +44,56 @@
    * @return {Promise} Promise resolving once the datastore values are loaded.
    */
   DataStore.prototype.load = function () {
-    var self = this;
-    return new Promise(function (resolve, reject) {
-      requestQueue.register(
-          CATMAID.makeURL('/client/datastores/' + self.name + '/'),
-          'GET',
-          {project_id: project ? project.id : undefined},
-          CATMAID.jsonResponseHandler(
-              function (data) {
-                self.entries = data.reduce(
-                    function (e, d) {
-                      if (d.project) {
-                        var scope = d.user ? 'USER_PROJECT' : 'PROJECT_DEFAULT';
-                      } else {
-                        var scope = d.user ? 'USER_DEFAULT' : 'GLOBAL';
-                      }
-
-                      if (!e.has(d.key)) {
-                        e.set(d.key, {});
-                      }
-
-                      try {
-                        var value = (typeof d.value === 'string' || d.value instanceof String) ?
-                            JSON.parse(d.value) :
-                            d.value;
-                        e.get(d.key)[scope] = {
-                          dirty: false,
-                          value: value
-                        };
-                      } catch (error) {
-                        // Do not alert the user, since this will not affect
-                        // other key/scopes and there is nothing explicit they
-                        // can do to correct it.
-                        console.log('Client data for store ' + d.key +
-                                    ', scope ' + scope + ' was not parsable.');
-                      }
-
-                      return e;
-                    },
-                    new Map());
-                self.trigger(DataStore.EVENT_LOADED, self);
-                resolve();
-              },
-              function (error) {
-                if (error.status === 404 || error.type === 'PermissionError') {
-                  self.entries = new Map();
-                  self.trigger(DataStore.EVENT_LOADED, self);
-                  resolve();
-                  return true;
-                } else {
-                  reject();
-                }
-              }));
-    });
+    return CATMAID.fetch({
+          url: `/client/datastores/${this.name}/`,
+          method: 'GET',
+          data: {
+            project_id: project ? project.id : undefined
+          },
+      })
+      .then(data => {
+        this.entries = data.reduce(
+            function (e, d) {
+              if (d.project) {
+                var scope = d.user ? 'USER_PROJECT' : 'PROJECT_DEFAULT';
+              } else {
+                var scope = d.user ? 'USER_DEFAULT' : 'GLOBAL';
+              }
+
+              if (!e.has(d.key)) {
+                e.set(d.key, {});
+              }
+
+              try {
+                var value = (typeof d.value === 'string' || d.value instanceof String) ?
+                    JSON.parse(d.value) :
+                    d.value;
+                e.get(d.key)[scope] = {
+                  dirty: false,
+                  value: value
+                };
+              } catch (error) {
+                // Do not alert the user, since this will not affect
+                // other key/scopes and there is nothing explicit they
+                // can do to correct it.
+                console.log('Client data for store ' + d.key +
+                            ', scope ' + scope + ' was not parsable.');
+              }
+
+              return e;
+            },
+            new Map());
+        this.trigger(DataStore.EVENT_LOADED, this);
+      })
+      .catch(error => {
+        if (error instanceof CATMAID.MissingResourceError ||
+            error instanceof CATMAID.PermissionError) {
+          this.entries = new Map();
+          this.trigger(DataStore.EVENT_LOADED, this);
+          return true;
+        }
+        return Promise.reject(error);
+      });
   };
 
   /**
@@ -161,27 +158,25 @@
   DataStore.prototype._store = function (key, scope) {
     var entry = this.entries.get(key)[scope];
     entry.dirty = false;
-    var self = this;
-    return new Promise(function (resolve, reject) {
-      requestQueue.register(
-          CATMAID.makeURL('/client/datastores/' + self.name + '/'),
-          'PUT',
-          {
-            project_id: (scope === 'USER_DEFAULT' ||
-                         scope === 'GLOBAL') ?
-                undefined : project.id,
-            ignore_user: scope === 'PROJECT_DEFAULT' ||
-                         scope === 'GLOBAL',
-            key: key,
-            value: JSON.stringify(entry.value)
-          },
-          CATMAID.jsonResponseHandler(resolve, reject, true));
-    }).catch(function (reason) {
-      if (reason && reason.status && reason.status === 403) {
-        console.log('Datastore lacks permissions to store for ' +
-                    'store: ' + self.name + ' key: ' + key + ' scope: ' + scope);
-      }
-    });
+    return CATMAID.fetch({
+        url: `/client/datastores/${this.name}/`,
+        method: 'PUT',
+        data: {
+          project_id: (scope === 'USER_DEFAULT' ||
+                       scope === 'GLOBAL') ?
+              undefined : project.id,
+          ignore_user: scope === 'PROJECT_DEFAULT' ||
+                       scope === 'GLOBAL',
+          key: key,
+          value: JSON.stringify(entry.value)
+        },
+      })
+      .catch(reason => {
+        if (reason && reason.status && reason.status === 403) {
+          console.log('Datastore lacks permissions to store for ' +
+                      `store: ${this.name} key: ${key} scope: ${scope}`);
+        }
+      });
   };
 
   /**
diff --git a/django/applications/catmaid/static/libs/catmaid/error.js b/django/applications/catmaid/static/libs/catmaid/error.js
index 8234dac299..44c6b0b83f 100644
--- a/django/applications/catmaid/static/libs/catmaid/error.js
+++ b/django/applications/catmaid/static/libs/catmaid/error.js
@@ -143,4 +143,9 @@
    */
   CATMAID.ReplacedRequestError = class ReplacedRequestError extends CATMAID.Error {};
 
+  /**
+   * Indicate a missing (remote) resource.
+   */
+  CATMAID.MissingResourceError = class MissingResourceError extends CATMAID.Error {};
+
 })(CATMAID);
diff --git a/django/applications/catmaid/static/libs/catmaid/settings-manager.js b/django/applications/catmaid/static/libs/catmaid/settings-manager.js
index 6c6a644988..0f531048aa 100644
--- a/django/applications/catmaid/static/libs/catmaid/settings-manager.js
+++ b/django/applications/catmaid/static/libs/catmaid/settings-manager.js
@@ -94,12 +94,13 @@
    *                             group and optional migrations between settings
    *                             version. See JSDoc for more.
    */
-  function Settings(name, schema) {
+  function Settings(name, schema, anonymousWriteBack = false) {
     this.name = name;
     this.schema = schema;
+    this.anonymousWriteBack = anonymousWriteBack;
     this.rendered = {};
     this.settingsStore = CATMAID.DataStoreManager.get(Settings.DATA_STORE_NAME);
-    this._boundLoad = this.load.bind(this);
+    this._boundLoad = this.load.bind(this, undefined);
     this._storeThrottleTimeout = null;
     this.settingsStore.on(CATMAID.DataStore.EVENT_LOADED, this._boundLoad);
     this.load();
@@ -128,9 +129,16 @@
    * Load settings values for all scopes by retrieving persisted values from
    * the DataStore and cascading values across scopes.
    *
+   * @param {Boolean} anonymousWriteBack (optional) Whether to write changed or
+   *                                     migrated settings back to the server if
+   *                                     the current user is not logged in.
+   *
    * @return {Promise} Promise yielding once loading is complete.
    */
-  Settings.prototype.load = function () {
+  Settings.prototype.load = function (anonymousWriteBack = undefined) {
+    if (anonymousWriteBack === undefined) {
+      anonymousWriteBack = this.anonymousWriteBack;
+    }
     var self = this;
     return this.settingsStore.get(this.name).then(function (stored) {
         var rendered = Object.keys(self.schema.entries).reduce(function (r, k) {
@@ -143,6 +151,8 @@
           return r;
         }, {});
 
+        let work = [];
+
         // For scope level, in order of increasing specificity, check
         // persisted settings, migrate them if necesssary, merge them if
         // possible, then create an object allowing direct access and
@@ -160,7 +170,8 @@
                     ' settings, resetting to defaults.');
                 scopeValues = {version: self.schema.version, entries: {}};
               }
-              self.settingsStore.set(self.name, scopeValues, datastoreScope, true);
+              let writeThrough = anonymousWriteBack || (!!CATMAID.session && CATMAID.session.is_authenticated);
+              work.push(self.settingsStore.set(self.name, scopeValues, datastoreScope, writeThrough));
             }
 
             Object.keys(scopeValues.entries).forEach(function (k) {
@@ -198,6 +209,8 @@
 
           self.rendered[scope] = $.extend(true, {}, rendered);
         });
+
+        return Promise.all(work);
     });
   };
 
diff --git a/django/applications/catmaid/tests/apis/test_datastores.py b/django/applications/catmaid/tests/apis/test_datastores.py
index 07ac407541..e2b50caa71 100644
--- a/django/applications/catmaid/tests/apis/test_datastores.py
+++ b/django/applications/catmaid/tests/apis/test_datastores.py
@@ -9,14 +9,14 @@ class DatastoresApiTests(CatmaidApiTestCase):
     def test_client_datastores(self):
         url = '/client/datastores/'
         response = self.client.get(url)
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 403)
         parsed_response = json.loads(response.content.decode('utf-8'))
         self.assertIn('error', parsed_response)
         self.assertIn('type', parsed_response)
         self.assertEquals('PermissionError', parsed_response['type'])
 
         response = self.client.post(url)
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 403)
         parsed_response = json.loads(response.content.decode('utf-8'))
         self.assertIn('error', parsed_response)
         self.assertIn('type', parsed_response)
@@ -26,7 +26,7 @@ def test_client_datastores(self):
         self.fake_authentication()
         name = 'test-  %% datastore'
         response = self.client.post(url, {'name': name})
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 500)
         parsed_response = json.loads(response.content.decode('utf-8'))
         self.assertTrue('error' in parsed_response)
         name = 'test-datastore'
diff --git a/django/applications/catmaid/tests/apis/test_links.py b/django/applications/catmaid/tests/apis/test_links.py
index d779a9e5d5..61613b1642 100644
--- a/django/applications/catmaid/tests/apis/test_links.py
+++ b/django/applications/catmaid/tests/apis/test_links.py
@@ -19,7 +19,7 @@ def test_delete_link_failure(self):
                 '/%d/link/delete' % self.test_project_id,
                 {'connector_id': connector_id, 'treenode_id': treenode_id,
                  'state': make_nocheck_state()})
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 400)
         parsed_response = json.loads(response.content.decode('utf-8'))
         expected_result = {'error': f'Could not find link between connector {connector_id} and node {treenode_id}'}
         self.assertIn('error', parsed_response)
diff --git a/django/applications/catmaid/tests/apis/test_messages.py b/django/applications/catmaid/tests/apis/test_messages.py
index 6d99961627..6fcc5cfaf7 100644
--- a/django/applications/catmaid/tests/apis/test_messages.py
+++ b/django/applications/catmaid/tests/apis/test_messages.py
@@ -13,7 +13,7 @@ def test_read_message_error(self):
         message_id = 5050
 
         response = self.client.post(f'/messages/{message_id}/mark_read')
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 404)
         parsed_response = json.loads(response.content.decode('utf-8'))
         self.assertIn('error', parsed_response)
         self.assertIn('type', parsed_response)
diff --git a/django/applications/catmaid/tests/apis/test_neurons.py b/django/applications/catmaid/tests/apis/test_neurons.py
index adf00106bc..bfab324a64 100644
--- a/django/applications/catmaid/tests/apis/test_neurons.py
+++ b/django/applications/catmaid/tests/apis/test_neurons.py
@@ -50,7 +50,7 @@ def test_rename_neuron_fail(self):
 
         url = '/%d/neurons/%s/rename' % (self.test_project_id, neuron_id)
         response = self.client.post(url, {'name': new_name})
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 403)
         parsed_response = json.loads(response.content.decode('utf-8'))
         self.assertTrue('error' in parsed_response)
         self.assertTrue(parsed_response['error'])
diff --git a/django/applications/catmaid/tests/apis/test_nodes.py b/django/applications/catmaid/tests/apis/test_nodes.py
index 478bb53785..ee0cbe5fec 100644
--- a/django/applications/catmaid/tests/apis/test_nodes.py
+++ b/django/applications/catmaid/tests/apis/test_nodes.py
@@ -157,7 +157,7 @@ def test_node_get_locations_wrong_project(self):
         response = self.client.post( '/%d/nodes/location' % (self.test_project_id + 1), {
             'node_ids': treenode_ids
         })
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 403)
         parsed_response = json.loads(response.content.decode('utf-8'))
         self.assertTrue('error' in parsed_response)
 
@@ -246,7 +246,7 @@ def test_node_update_invalid_location(self):
                         't[0][1]': x,
                         't[0][2]': y,
                         't[0][3]': z})
-            self.assertEqual(response.status_code, 200)
+            self.assertEqual(response.status_code, 400)
             parsed_response = json.loads(response.content.decode('utf-8'))
             self.assertIn('error', parsed_response)
             cursor = connection.cursor()
@@ -351,7 +351,7 @@ def insert_params(dictionary, param_id, params):
 
         response = self.client.post(
                 '/%d/node/update' % self.test_project_id, param_dict)
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 403)
         parsed_response = json.loads(response.content.decode('utf-8'))
         expected_result = {'error': 'User test2 cannot edit all of the 4 '
                            'unique objects from table treenode'}
diff --git a/django/applications/catmaid/tests/apis/test_skeletons.py b/django/applications/catmaid/tests/apis/test_skeletons.py
index 1643ce57ea..bc19f75fef 100644
--- a/django/applications/catmaid/tests/apis/test_skeletons.py
+++ b/django/applications/catmaid/tests/apis/test_skeletons.py
@@ -111,7 +111,7 @@ def test_import_skeleton(self):
                 {'file.swc': swc_file2, 'name': 'test2', 'neuron_id':
                     neuron.id, 'auto_id': False})
 
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 400)
         parsed_response = json.loads(response.content.decode('utf-8'))
         expected_result = {
                 "error": "The passed in neuron ID is already in use and neither of the parameters force or auto_id are set to true."}
@@ -185,7 +185,7 @@ def test_import_skeleton(self):
                 {'file.swc': swc_file2, 'name': 'test2', 'skeleton_id':
                     skeleton.id, 'auto_id': False})
 
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 400)
         parsed_response = json.loads(response.content.decode('utf-8'))
         expected_result = {
                 "error": "The passed in skeleton ID is already in use and neither of the parameters force or auto_id are set to true."}
@@ -365,7 +365,7 @@ def test_split_skeleton_annotations(self):
             {'treenode_id': 2394,
              'upstream_annotation_map':   json.dumps({'A': self.test_user_id}),
              'downstream_annotation_map': json.dumps({'C': self.test_user_id})})
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 400)
         parsed_response = json.loads(response.content.decode('utf-8'))
         expected_result = "Annotation distribution is not valid for splitting. " \
                           "One part has to keep the whole set of annotations!"
@@ -378,7 +378,7 @@ def test_split_skeleton_annotations(self):
             {'treenode_id': 2394,
              'upstream_annotation_map':   json.dumps({'A': self.test_user_id, 'B': self.test_user_id}),
              'downstream_annotation_map': json.dumps({'C': self.test_user_id, 'B': self.test_user_id})})
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 400)
         parsed_response = json.loads(response.content.decode('utf-8'))
         expected_result = "Annotation distribution is not valid for splitting. " \
                           "One part has to keep the whole set of annotations!"
@@ -813,7 +813,7 @@ def test_skeleton_graph(self):
         # Confidence split
         # Change confidence that affects 1 edge from 235 to 373
         response = self.client.post('/%d/treenodes/289/confidence' % self.test_project_id,
-            {'new_confidence': 3})
+                {'new_confidence': 3, 'state': '{"nocheck": true}'})
         self.assertEqual(response.status_code, 200)
         # Add confidence criteria, but not one that should affect the graph.
         response = self.client.post(
@@ -841,10 +841,11 @@ def test_skeleton_graph(self):
              'skeleton_ids[2]': skeleton_ids[2],
              'confidence_threshold': 4})
         parsed_response = json.loads(response.content.decode('utf-8'))
-        expected_result_nodes = frozenset(['235', '361', '373'])
+        expected_result_nodes = frozenset(['235_1', '235_2', '361', '373'])
         expected_result_edges = [
-                ['235', '373', [0, 0, 0, 0, 2]],
-                ['235', '361', [0, 0, 0, 0, 1]]]
+                ['235_1', '373', [0, 0, 0, 0, 1]],
+                ['235_2', '373', [0, 0, 0, 0, 1]],
+                ['235_2', '361', [0, 0, 0, 0, 1]]]
 
         self.assertEqual(expected_result_nodes, frozenset(parsed_response['nodes']))
         # Since order is not important, check length and matches separately.
@@ -864,10 +865,11 @@ def test_skeleton_graph(self):
              'confidence_threshold': 4,
              'bandwidth': 2000})
         parsed_response = json.loads(response.content.decode('utf-8'))
-        expected_result_nodes = frozenset(['361', '373', '235_1', '235_2'])
+        expected_result_nodes = frozenset(['361', '373', '235_1', '235_2_2', '235_2_3'])
         expected_result_edges = [
-                ['235_1', '373', [0, 0, 0, 0, 2]],
-                ['235_1', '361', [0, 0, 0, 0, 1]]]
+                ['235_1', '373', [0, 0, 0, 0, 1]],
+                ['235_2_2', '373', [0, 0, 0, 0, 1]],
+                ['235_2_2', '361', [0, 0, 0, 0, 1]]]
 
         self.assertEqual(expected_result_nodes, frozenset(parsed_response['nodes']))
         # Since order is not important, check length and matches separately.
@@ -896,7 +898,8 @@ def test_skeleton_graph(self):
              'confidence_threshold': 4})
         parsed_response = json.loads(response.content.decode('utf-8'))
         expected_result_edges = [
-                ['235', '373', [0, 0, 0, 0, 2]]]
+                ['235_1', '373', [0, 0, 0, 0, 1]],
+                ['235_2', '373', [0, 0, 0, 0, 1]]]
         # Since order is not important, check length and matches separately.
         self.assertEqual(len(expected_result_edges), len(parsed_response['edges']))
         for row in expected_result_edges:
diff --git a/django/applications/catmaid/tests/apis/test_textlabels.py b/django/applications/catmaid/tests/apis/test_textlabels.py
index f54cb25ff0..bf13b60477 100644
--- a/django/applications/catmaid/tests/apis/test_textlabels.py
+++ b/django/applications/catmaid/tests/apis/test_textlabels.py
@@ -101,7 +101,7 @@ def test_update_textlabel_failure(self):
         response = self.client.post(
                 '/%d/textlabel/update' % self.test_project_id,
                 params)
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 400)
         parsed_response = json.loads(response.content.decode('utf-8'))
         expected_result = 'Failed to find Textlabel with id %s.' % textlabel_id
         self.assertIn('error', parsed_response)
diff --git a/django/applications/catmaid/tests/apis/test_treenodes.py b/django/applications/catmaid/tests/apis/test_treenodes.py
index 4fe3d4af3d..329646486d 100644
--- a/django/applications/catmaid/tests/apis/test_treenodes.py
+++ b/django/applications/catmaid/tests/apis/test_treenodes.py
@@ -32,7 +32,7 @@ def test_fail_update_confidence(self):
         response = self.client.post(
                 '/%d/treenodes/%d/confidence' % (self.test_project_id, treenode_id),
                 {'new_confidence': '4'})
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 400)
         expected_result = 'No skeleton and neuron for treenode %s' % treenode_id
         parsed_response = json.loads(response.content.decode('utf-8'))
         self.assertEqual(expected_result, parsed_response['error'])
@@ -288,7 +288,7 @@ def test_create_treenode_with_nonexisting_parent_failure(self):
             'parent_id': parent_id,
             'radius': 2,
             'state': make_nocheck_state()})
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 400)
         parsed_response = json.loads(response.content.decode('utf-8'))
         expected_result = {'error': 'Parent treenode %d does not exist' % parent_id}
         self.assertIn(expected_result['error'], parsed_response['error'])
@@ -335,7 +335,7 @@ def test_delete_root_treenode_with_children_failure(self):
         response = self.client.post(
                 '/%d/treenode/delete' % self.test_project_id,
                 {'treenode_id': treenode_id, 'state': make_nocheck_state()})
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 400)
         parsed_response = json.loads(response.content.decode('utf-8'))
         expected_result = "Could not delete root node: You can't delete the " \
                           "root node when it has children."
@@ -497,7 +497,7 @@ def test_insert_treenoded_not_on_edge_without_permission(self):
             'child_id': child_id,
             'parent_id': parent_id})
 
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 403)
         parsed_response = json.loads(response.content.decode('utf-8'))
         self.assertTrue('error' in parsed_response)
 
@@ -539,7 +539,7 @@ def test_insert_treenoded_no_child_parent(self):
             'child_id': child_id,
             'parent_id': parent_id})
 
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 400)
         parsed_response = json.loads(response.content.decode('utf-8'))
         self.assertTrue('error' in parsed_response)
 
@@ -635,7 +635,7 @@ def test_treenode_info_nonexisting_treenode_failure(self):
 
         response = self.client.get(
                 '/%d/treenodes/%s/info' % (self.test_project_id, treenode_id))
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 400)
         parsed_response = json.loads(response.content.decode('utf-8'))
         expected_result = 'No skeleton and neuron for treenode %s' % treenode_id
         self.assertIn('error', parsed_response)
diff --git a/django/applications/catmaid/tests/gui/test_basic_gui.py b/django/applications/catmaid/tests/gui/test_basic_gui.py
index ad411151f6..32f1b49490 100644
--- a/django/applications/catmaid/tests/gui/test_basic_gui.py
+++ b/django/applications/catmaid/tests/gui/test_basic_gui.py
@@ -188,9 +188,14 @@ def test_home_page_login_logout(self):
                 # Let test fail
                 self.assertNotIn('SyntaxError', log_entry['message'])
 
-            # Fail on any severe errors
+            # Fail on any severe errors that aren't expected. Expected are 403
+            # errors for settings loading for the anonymous user if not linked
+            # to any project.
             self.assertIn('level', log_entry)
-            self.assertNotIn('SEVERE', log_entry['level'], log_entry['message'])
+            unexpected_error = 'SEVERE' in log_entry['level'] and \
+                    '403 (Forbidden)' not in log_entry['message']
+            if unexpected_error:
+                self.assertNotIn('SEVERE', log_entry['level'], log_entry['message'])
 
         # Check title
         self.assertTrue("CATMAID" in self.selenium.title)
diff --git a/django/applications/catmaid/tests/test_common_apis.py b/django/applications/catmaid/tests/test_common_apis.py
index 409cae9442..015c95de8c 100644
--- a/django/applications/catmaid/tests/test_common_apis.py
+++ b/django/applications/catmaid/tests/test_common_apis.py
@@ -328,7 +328,7 @@ def test_user_list_with_passwords_regular_user(self):
             'with_passwords': True,
         })
 
-        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.status_code, 403)
         parsed_response = json.loads(response.content.decode('utf-8'))
 
         self.assertTrue('error' in parsed_response)
@@ -693,7 +693,7 @@ def test_can_browse_access(self):
         for api in self.can_browse_get_api:
             msg = "GET %s" % api
             response = self.client.get(api)
-            self.assertEqual(response.status_code, 200, msg)
+            self.assertNotIn(response.status_code, (401, 403), msg)
             try:
                 parsed_response = json.loads(response.content.decode('utf-8'))
                 missing_permissions = ('error' in parsed_response and
@@ -709,7 +709,7 @@ def test_can_browse_access(self):
         for api in self.can_browse_post_api:
             msg = "POST %s" % api
             response = self.client.post(api)
-            self.assertEqual(response.status_code, 200, msg)
+            self.assertNotIn(response.status_code, (401, 403), msg)
             try:
                 parsed_response = json.loads(response.content.decode('utf-8'))
                 missing_permissions = ('error' in parsed_response and
diff --git a/django/lib/custom_testrunner.py b/django/lib/custom_testrunner.py
index bdd17fa998..726a5cbe15 100644
--- a/django/lib/custom_testrunner.py
+++ b/django/lib/custom_testrunner.py
@@ -2,8 +2,16 @@
 
 from django.conf import settings
 from django.test.runner import DiscoverRunner
+from pipeline.conf import settings as pipeline_settings
 
 class TestSuiteRunner(DiscoverRunner):
+
     def __init__(self, *args, **kwargs):
         settings.TESTING_ENVIRONMENT = True
         super(TestSuiteRunner, self).__init__(*args, **kwargs)
+
+    def setup_test_environment(self, **kwargs):
+        '''Override STATICFILES_STORAGE and pipeline DEBUG.'''
+        super().setup_test_environment(**kwargs)
+        settings.STATICFILES_STORAGE = 'pipeline.storage.NonPackagingPipelineStorage'
+        pipeline_settings.DEBUG = True