diff --git a/swh/lister/bitbucket/tasks.py b/swh/lister/bitbucket/tasks.py
--- a/swh/lister/bitbucket/tasks.py
+++ b/swh/lister/bitbucket/tasks.py
@@ -14,13 +14,13 @@
 def list_bitbucket_incremental(**lister_args):
     '''Incremental update of the BitBucket forge'''
     lister = BitBucketLister(**lister_args)
-    lister.run(min_bound=lister.db_last_index(), max_bound=None)
+    return lister.run(min_bound=lister.db_last_index(), max_bound=None)
 
 
 @shared_task(name=__name__ + '.RangeBitBucketLister')
 def _range_bitbucket_lister(start, end, **lister_args):
     lister = BitBucketLister(**lister_args)
-    lister.run(min_bound=start, max_bound=end)
+    return lister.run(min_bound=start, max_bound=end)
 
 
 @shared_task(name=__name__ + '.FullBitBucketRelister', bind=True)
@@ -44,6 +44,7 @@
         promise.save()  # so that we can restore the GroupResult in tests
     except (NotImplementedError, AttributeError):
         self.log.info('Unable to call save_group with current result backend.')
+    # FIXME: what to do in terms of return here?
     return promise.id
 
 
diff --git a/swh/lister/cgit/lister.py b/swh/lister/cgit/lister.py
--- a/swh/lister/cgit/lister.py
+++ b/swh/lister/cgit/lister.py
@@ -78,6 +78,7 @@
         }
 
     def run(self):
+        status = 'uneventful'
         total = 0
         for repos in grouper(self.get_repos(), 10):
             models = list(filter(None, (self.build_model(repo)
@@ -87,6 +88,9 @@
             self.db_session.commit()
             total += len(injected_repos)
             logger.debug('Scheduled %s tasks for %s', total, self.url)
+            status = 'eventful'
+
+        return {'status': status}
 
     def get_repos(self):
         """Generate git 'project' URLs found on the current CGit server
diff --git a/swh/lister/cgit/tasks.py b/swh/lister/cgit/tasks.py
--- a/swh/lister/cgit/tasks.py
+++ b/swh/lister/cgit/tasks.py
@@ -10,7 +10,7 @@
 @shared_task(name=__name__ + '.CGitListerTask')
 def list_cgit(**lister_args):
     '''Lister task for CGit instances'''
-    CGitLister(**lister_args).run()
+    return CGitLister(**lister_args).run()
 
 
 @shared_task(name=__name__ + '.ping')
diff --git a/swh/lister/core/indexing_lister.py b/swh/lister/core/indexing_lister.py
--- a/swh/lister/core/indexing_lister.py
+++ b/swh/lister/core/indexing_lister.py
@@ -213,6 +213,7 @@
         Returns:
             nothing
         """
+        status = 'uneventful'
         self.min_index = min_bound
         self.max_index = max_bound
 
@@ -243,9 +244,11 @@
                 logger.debug('Flushing updates at index %s', i)
                 self.db_session.commit()
                 self.db_session = self.mk_session()
+                status = 'eventful'
 
         self.db_session.commit()
         self.db_session = self.mk_session()
+        return {'status': status}
 
 
 class IndexingHttpLister(ListerHttpTransport, IndexingLister):
diff --git a/swh/lister/core/page_by_page_lister.py b/swh/lister/core/page_by_page_lister.py
--- a/swh/lister/core/page_by_page_lister.py
+++ b/swh/lister/core/page_by_page_lister.py
@@ -110,6 +110,7 @@
             nothing
 
         """
+        status = 'uneventful'
         page = min_bound or 0
         loop_count = 0
 
@@ -127,6 +128,7 @@
             elif not injected_repos:
                 logging.info('Repositories already seen, stopping')
                 break
+            status = 'eventful'
 
             next_page = self.get_next_target_from_response(response)
 
@@ -149,6 +151,8 @@
         self.db_session.commit()
         self.db_session = self.mk_session()
 
+        return {'status': status}
+
 
 class PageByPageHttpLister(ListerHttpTransport, PageByPageLister):
     """Convenience class for ensuring right lookup and init order when
diff --git a/swh/lister/core/simple_lister.py b/swh/lister/core/simple_lister.py
--- a/swh/lister/core/simple_lister.py
+++ b/swh/lister/core/simple_lister.py
@@ -89,3 +89,8 @@
         response, injected_repos = self.ingest_data(dump_not_used_identifier)
         if not response and not injected_repos:
             logging.info('No response from api server, stopping')
+            status = 'uneventful'
+        else:
+            status = 'eventful'
+
+        return {'status': status}
diff --git a/swh/lister/cran/tasks.py b/swh/lister/cran/tasks.py
--- a/swh/lister/cran/tasks.py
+++ b/swh/lister/cran/tasks.py
@@ -10,7 +10,7 @@
 @shared_task(name=__name__ + '.CRANListerTask')
 def list_cran(**lister_args):
     '''Lister task for the CRAN registry'''
-    CRANLister(**lister_args).run()
+    return CRANLister(**lister_args).run()
 
 
 @shared_task(name=__name__ + '.ping')
diff --git a/swh/lister/debian/lister.py b/swh/lister/debian/lister.py
--- a/swh/lister/debian/lister.py
+++ b/swh/lister/debian/lister.py
@@ -216,12 +216,14 @@
                            .one_or_none()
 
         if not distribution:
-            raise ValueError("Distribution %s is not registered" %
-                             self.distribution)
+            logger.error("Distribution %s is not registered" %
+                         self.distribution)
+            return {'status': 'failed'}
 
         if not distribution.type == 'deb':
-            raise ValueError("Distribution %s is not a Debian derivative" %
-                             distribution)
+            logger.error("Distribution %s is not a Debian derivative" %
+                         distribution)
+            return {'status': 'failed'}
 
         date = self.date
 
@@ -250,4 +252,4 @@
 
         self.db_session.commit()
 
-        return True
+        return {'status': 'eventful'}
diff --git a/swh/lister/debian/tasks.py b/swh/lister/debian/tasks.py
--- a/swh/lister/debian/tasks.py
+++ b/swh/lister/debian/tasks.py
@@ -10,7 +10,7 @@
 @shared_task(name=__name__ + '.DebianListerTask')
 def list_debian_distribution(distribution, **lister_args):
     '''List a Debian distribution'''
-    DebianLister(distribution=distribution, **lister_args).run()
+    return DebianLister(distribution=distribution, **lister_args).run()
 
 
 @shared_task(name=__name__ + '.ping')
diff --git a/swh/lister/github/tasks.py b/swh/lister/github/tasks.py
--- a/swh/lister/github/tasks.py
+++ b/swh/lister/github/tasks.py
@@ -15,13 +15,13 @@
 def list_github_incremental(**lister_args):
     'Incremental update of GitHub'
     lister = GitHubLister(**lister_args)
-    lister.run(min_bound=lister.db_last_index(), max_bound=None)
+    return lister.run(min_bound=lister.db_last_index(), max_bound=None)
 
 
 @shared_task(name=__name__ + '.RangeGitHubLister')
 def _range_github_lister(start, end, **lister_args):
     lister = GitHubLister(**lister_args)
-    lister.run(min_bound=start, max_bound=end)
+    return lister.run(min_bound=start, max_bound=end)
 
 
 @shared_task(name=__name__ + '.FullGitHubRelister', bind=True)
@@ -44,6 +44,7 @@
         promise.save()  # so that we can restore the GroupResult in tests
     except (NotImplementedError, AttributeError):
         self.log.info('Unable to call save_group with current result backend.')
+    # FIXME: what to do in terms of return here?
     return promise.id
 
 
diff --git a/swh/lister/gitlab/tasks.py b/swh/lister/gitlab/tasks.py
--- a/swh/lister/gitlab/tasks.py
+++ b/swh/lister/gitlab/tasks.py
@@ -20,13 +20,13 @@
     lister = GitLabLister(**lister_args)
     total_pages = lister.get_pages_information()[1]
     # stopping as soon as existing origins for that instance are detected
-    lister.run(min_bound=1, max_bound=total_pages, check_existence=True)
+    return lister.run(min_bound=1, max_bound=total_pages, check_existence=True)
 
 
 @shared_task(name=__name__ + '.RangeGitLabLister')
 def _range_gitlab_lister(start, end, **lister_args):
     lister = GitLabLister(**lister_args)
-    lister.run(min_bound=start, max_bound=end)
+    return lister.run(min_bound=start, max_bound=end)
 
 
 @shared_task(name=__name__ + '.FullGitLabRelister', bind=True)
@@ -43,6 +43,7 @@
         promise.save()
     except (NotImplementedError, AttributeError):
         self.log.info('Unable to call save_group with current result backend.')
+    # FIXME: what to do in terms of return here?
     return promise.id
 
 
diff --git a/swh/lister/gnu/tasks.py b/swh/lister/gnu/tasks.py
--- a/swh/lister/gnu/tasks.py
+++ b/swh/lister/gnu/tasks.py
@@ -9,8 +9,8 @@
 
 @shared_task(name=__name__ + '.GNUListerTask')
 def list_gnu_full(**lister_args):
-    'List lister for the GNU source code archive'
-    GNULister(**lister_args).run()
+    """List lister for the GNU source code archive"""
+    return GNULister(**lister_args).run()
 
 
 @shared_task(name=__name__ + '.ping')
diff --git a/swh/lister/npm/tasks.py b/swh/lister/npm/tasks.py
--- a/swh/lister/npm/tasks.py
+++ b/swh/lister/npm/tasks.py
@@ -45,7 +45,7 @@
     'Full lister for the npm (javascript) registry'
     lister = NpmLister(**lister_args)
     with save_registry_state(lister):
-        lister.run()
+        return lister.run()
 
 
 @shared_task(name=__name__ + '.NpmIncrementalListerTask')
@@ -54,7 +54,7 @@
     lister = NpmIncrementalLister(**lister_args)
     update_seq_start = get_last_update_seq(lister)
     with save_registry_state(lister):
-        lister.run(min_bound=update_seq_start)
+        return lister.run(min_bound=update_seq_start)
 
 
 @shared_task(name=__name__ + '.ping')
diff --git a/swh/lister/phabricator/tasks.py b/swh/lister/phabricator/tasks.py
--- a/swh/lister/phabricator/tasks.py
+++ b/swh/lister/phabricator/tasks.py
@@ -9,8 +9,8 @@
 
 @shared_task(name=__name__ + '.FullPhabricatorLister')
 def list_phabricator_full(**lister_args):
-    'Full update of a Phabricator instance'
-    PhabricatorLister(**lister_args).run()
+    """Full update of a Phabricator instance"""
+    return PhabricatorLister(**lister_args).run()
 
 
 @shared_task(name=__name__ + '.ping')
diff --git a/swh/lister/pypi/tasks.py b/swh/lister/pypi/tasks.py
--- a/swh/lister/pypi/tasks.py
+++ b/swh/lister/pypi/tasks.py
@@ -10,7 +10,7 @@
 @shared_task(name=__name__ + '.PyPIListerTask')
 def list_pypi(**lister_args):
     'Full update of the PyPI (python) registry'
-    PyPILister(**lister_args).run()
+    return PyPILister(**lister_args).run()
 
 
 @shared_task(name=__name__ + '.ping')