diff --git a/git_time_tracker/source/csv_file.py b/git_time_tracker/source/csv_file.py
index ab36b66..5e26973 100644
--- a/git_time_tracker/source/csv_file.py
+++ b/git_time_tracker/source/csv_file.py
@@ -10,7 +10,8 @@ logger = getLogger(__name__)
 
 
 def iterate_samples_from_dicts(rows: list[dict[str, Any]]) -> Iterator[ActivitySample]:
-    assert len(rows) > 0
+    if len(rows) == 0:
+        raise ValueError("No rows provided")
 
     if True:
         event_data = rows[len(rows) // 2]  # Hopefully select a useful representative.
@@ -18,8 +19,8 @@ def iterate_samples_from_dicts(rows: list[dict[str, Any]]) -> Iterator[ActivityS
         logger.info('Found possible keys: %s', possible_keys)
         del event_data
 
-    assert len(possible_keys.time_start) + len(possible_keys.time_end) >= 1
-    assert len(possible_keys.image) >= 0
+    if len(possible_keys.time_start) + len(possible_keys.time_end) < 1:
+        raise ValueError("No time columns found in data")
 
     for event_data in rows:
         """
@@ -46,5 +47,6 @@ def iterate_samples_from_dicts(rows: list[dict[str, Any]]) -> Iterator[ActivityS
 def iterate_samples_from_csv_file(file_path: Path) -> Iterator[ActivitySample]:
     dicts = load_csv_file(file_path)
     samples = list(iterate_samples_from_dicts(dicts))
-    assert len(samples) > 0, 'Did not found any samples'
+    if len(samples) == 0:
+        raise ValueError('Did not find any samples')
     yield from samples
diff --git a/git_time_tracker/source/git_repo.py b/git_time_tracker/source/git_repo.py
index 2e06c71..b11d4de 100644
--- a/git_time_tracker/source/git_repo.py
+++ b/git_time_tracker/source/git_repo.py
@@ -27,7 +27,8 @@ def determine_project_name(repo: git.Repo) -> str:
 
 def get_samples_from_project(repo: git.Repo) -> Iterator[ActivitySample]:
     project_name = determine_project_name(repo)
-    assert project_name is not None
+    if project_name is None:
+        raise ValueError("Could not determine project name")
 
     # TODO: Branch on main or master or default
 
diff --git a/personal_data/util.py b/personal_data/util.py
index 9a2f9d8..04072fb 100644
--- a/personal_data/util.py
+++ b/personal_data/util.py
@@ -101,7 +101,8 @@ def dataclass_to_dict(obj) -> dict[str, Any]:
 def normalize_dict(d: dict[str, Any] | frozendict[str, Any]) -> frozendict[str, Any]:
     if not isinstance(d, dict) and not isinstance(d, frozendict):
         d = dataclass_to_dict(d)
-    assert isinstance(d, dict) or isinstance(d, frozendict), 'Not a dict'
+    if not isinstance(d, (dict, frozendict)):
+        raise TypeError('Expected dict or frozendict')
     safe_values = [
         (k, csv_import.csv_str_to_value(csv_import.csv_safe_value(v)))
         for k, v in d.items()