diff --git a/backend/fsutil.py b/backend/fsutil.py
new file mode 100644
index 0000000..9c99f0d
--- /dev/null
+++ b/backend/fsutil.py
@@ -0,0 +1,22 @@
+"""Atomare Datei-Writes: erst .tmp im selben Verzeichnis, dann os.replace.
+
+Ein Crash hinterlässt höchstens eine .tmp-Datei — nie eine halb geschriebene
+Zieldatei. Die .tmp wird beim nächsten erfolgreichen Write überschrieben.
+"""
+
+import json
+import os
+from pathlib import Path
+
+
+def atomic_write_text(path: Path, text: str) -> None:
+    tmp = path.with_name(path.name + ".tmp")
+    with open(tmp, "w", encoding="utf-8") as f:
+        f.write(text)
+        f.flush()
+        os.fsync(f.fileno())
+    os.replace(tmp, path)
+
+
+def atomic_write_json(path: Path, obj, **dumps_kwargs) -> None:
+    atomic_write_text(path, json.dumps(obj, ensure_ascii=False, **dumps_kwargs))
diff --git a/backend/generator.py b/backend/generator.py
index 470b32d..917e073 100644
--- a/backend/generator.py
+++ b/backend/generator.py
@@ -18,6 +18,7 @@ from config import (
     MAX_CONCURRENT_GENERATIONS,
 )
 from database import update_guide
+from fsutil import atomic_write_json, atomic_write_text
 from paths import arbeit_dir, bausteine_path, guide_content_path, project_dir
 
 _semaphore = asyncio.Semaphore(MAX_CONCURRENT_GENERATIONS)
@@ -580,10 +581,7 @@ async def generate_bausteine(topic: str, instructions: str = "", provider: str =
 
             # Titel eindeutig machen und unsortiertes Inventar schreiben
             entries = _eindeutige_titel(entries)
-            final_path.write_text(
-                "\n".join(f"{i}. {t}" for i, t in entries.items()) + "\n",
-                encoding="utf-8",
-            )
+            atomic_write_text(final_path, "\n".join(f"{i}. {t}" for i, t in entries.items()) + "\n")
     except Exception as e:
         log.exception("[%s] Bausteine-Generierung fehlgeschlagen", topic)
         _bausteine_errors[topic] = str(e)[:2000]
@@ -937,10 +935,7 @@ async def _generate_onepager(
                 return None
             if res is None:
                 _log(topic, "OnePager-Fix ungültig — ursprüngliche Karten bleiben")
-                karten_path.write_text(
-                    json.dumps({"karten": {k["key"]: {"titel": k["titel"], "md": k["md"]} for k in karten}}, ensure_ascii=False),
-                    encoding="utf-8",
-                )
+                atomic_write_json(karten_path, {"karten": {k["key"]: {"titel": k["titel"], "md": k["md"]} for k in karten}})
             else:
                 karten = res[0]
 
@@ -1041,7 +1036,7 @@ async def _generate_sections(
                 return None
             if res is None:
                 _log(topic, "Auswahl-Fix ungültig — ursprüngliche Auswahl bleibt")
-                files["auswahl"].write_text(auswahl_json(), encoding="utf-8")
+                atomic_write_text(files["auswahl"], auswahl_json())
             else:
                 auswahl = res[0]
 
@@ -1122,7 +1117,7 @@ async def _generate_sections(
                 return None
             if res is None:
                 _log(topic, "Gliederungs-Fix ungültig — ursprüngliche Gliederung bleibt")
-                files["gliederung"].write_text(gliederung_json(), encoding="utf-8")
+                atomic_write_text(files["gliederung"], gliederung_json())
             else:
                 plan = res[0]
 
@@ -1310,10 +1305,7 @@ async def generate_guide(guide_id: str, topic: str, format_name: str, instructio
             if chapters is None or guide_id in _cancelled:
                 return
 
-            content_path.write_text(
-                json.dumps({"topic": topic, "format": format_name, "chapters": chapters}, ensure_ascii=False, indent=1),
-                encoding="utf-8",
-            )
+            atomic_write_json(content_path, {"topic": topic, "format": format_name, "chapters": chapters}, indent=1)
 
             now = datetime.now(timezone.utc).isoformat()
             await update_guide(guide_id, status="done", progress=None, step=None, updated_at=now)