diff --git a/3.snapshot_comparator/src/snapshot_comparator/core.py b/3.snapshot_comparator/src/snapshot_comparator/core.py
new file mode 100644
index 0000000..4a79e33
--- /dev/null
+++ b/3.snapshot_comparator/src/snapshot_comparator/core.py
@@ -0,0 +1,83 @@
+from dataclasses import dataclass
+from typing import List, Dict, Any
+import logging
+
+__all__ = ["Snapshot", "compare_snapshots"]
+
+
+@dataclass
+class Snapshot:
+    artifact_key: str
+    status_before: str
+    status_after: str
+
+
+class SnapshotValidationError(Exception):
+    """Custom exception raised when snapshot validation fails."""
+
+
+logger = logging.getLogger(__name__)
+if not logger.handlers:
+    handler = logging.StreamHandler()
+    formatter = logging.Formatter("%(asctime)s - %(levelname)s - %(message)s")
+    handler.setFormatter(formatter)
+    logger.addHandler(handler)
+logger.setLevel(logging.INFO)
+
+
+def _validate_snapshot(snapshot: Any) -> Snapshot:
+    """Validates and converts a raw snapshot dict or object into a Snapshot instance."""
+    if isinstance(snapshot, Snapshot):
+        return snapshot
+    if not isinstance(snapshot, dict):
+        raise SnapshotValidationError(f"Snapshot must be dict or Snapshot, got {type(snapshot)}")
+
+    required_fields = ["artifact_key", "status_before", "status_after"]
+    for field in required_fields:
+        if field not in snapshot:
+            raise SnapshotValidationError(f"Missing required field '{field}' in snapshot")
+        if not isinstance(snapshot[field], str):
+            raise SnapshotValidationError(f"Field '{field}' must be of type str")
+    return Snapshot(
+        artifact_key=snapshot["artifact_key"],
+        status_before=snapshot["status_before"],
+        status_after=snapshot["status_after"]
+    )
+
+
+def compare_snapshots(snapshot1: List[Any], snapshot2: List[Any]) -> Dict[str, Dict[str, str]]:
+    """Vergleicht zwei Snapshot-Listen und liefert eine Differenz der Artefaktzustände.
+
+    Args:
+        snapshot1: Liste von Snapshot-Objekten oder -Dicts vor Δt.
+        snapshot2: Liste von Snapshot-Objekten oder -Dicts nach Δt.
+
+    Returns:
+        Dict[str, Dict[str, str]]: Differenzen nach artifact_key, 
+            z.B. {"artifactA": {"before": "missing", "after": "present"}}.
+    """
+    assert isinstance(snapshot1, list), "snapshot1 must be a list"
+    assert isinstance(snapshot2, list), "snapshot2 must be a list"
+
+    logger.info("Validating and indexing snapshots ...")
+    snap1_valid = [_validate_snapshot(s) for s in snapshot1]
+    snap2_valid = [_validate_snapshot(s) for s in snapshot2]
+
+    index1 = {s.artifact_key: s for s in snap1_valid}
+    index2 = {s.artifact_key: s for s in snap2_valid}
+
+    all_keys = set(index1.keys()) | set(index2.keys())
+    diff: Dict[str, Dict[str, str]] = {}
+
+    for key in all_keys:
+        before = index1.get(key)
+        after = index2.get(key)
+
+        status_before = before.status_after if before else "missing"
+        status_after = after.status_after if after else "missing"
+
+        if status_before != status_after:
+            diff[key] = {"before": status_before, "after": status_after}
+
+    logger.info(f"Found {len(diff)} differences between snapshots.")
+    return diff