diff --git a/backend/app/modules/editor/domain/entities.py b/backend/app/modules/editor/domain/entities.py
index e69de29..f98c57c 100644
--- a/backend/app/modules/editor/domain/entities.py
+++ b/backend/app/modules/editor/domain/entities.py
@@ -0,0 +1,22 @@
+from dataclasses import dataclass
+from datetime import datetime
+
+
+@dataclass
+class EditableFile:
+    path: str
+    format: str         # csv, md, yaml, openapi
+    content: str
+    last_modified: datetime
+
+
+@dataclass
+class AffectedFile:
+    path: str
+    reason: str
+
+
+@dataclass
+class ImpactResult:
+    source_file: str
+    affected_files: list[AffectedFile]
diff --git a/backend/app/modules/editor/infrastructure/file_io.py b/backend/app/modules/editor/infrastructure/file_io.py
new file mode 100644
index 0000000..7a41a2f
--- /dev/null
+++ b/backend/app/modules/editor/infrastructure/file_io.py
@@ -0,0 +1,35 @@
+from datetime import datetime, timezone
+from pathlib import Path
+
+from app.modules.editor.domain.entities import EditableFile
+from app.shared.infrastructure.filesystem import read_text, write_text
+
+
+def detect_format(file_path: Path) -> str:
+    suffix = file_path.suffix.lower()
+    if suffix == ".csv":
+        return "csv"
+    elif suffix == ".md":
+        return "md"
+    elif suffix in (".yaml", ".yml"):
+        if "openapi" in file_path.name or "api-contracts" in file_path.name:
+            return "openapi"
+        return "yaml"
+    return "unknown"
+
+
+def read_file(base_dir: Path, relative_path: str) -> EditableFile:
+    full_path = base_dir / relative_path
+    content = read_text(full_path)
+    stat = full_path.stat()
+    return EditableFile(
+        path=relative_path,
+        format=detect_format(full_path),
+        content=content,
+        last_modified=datetime.fromtimestamp(stat.st_mtime, tz=timezone.utc),
+    )
+
+
+def write_file(base_dir: Path, relative_path: str, content: str) -> None:
+    full_path = base_dir / relative_path
+    write_text(full_path, content)