diff --git a/core/annotations.py b/core/annotations.py
new file mode 100644
index 0000000..af1a694
--- /dev/null
+++ b/core/annotations.py
@@ -0,0 +1,55 @@
+import json
+import os
+
+
+def build_annotation_json_path(folder: str) -> str:
+    return os.path.join(folder, "dataset.json")
+
+
+def remove_clip_annotation(folder: str, clip_path: str) -> None:
+    """Remove the entry for *clip_path* from <folder>/dataset.json if present."""
+    json_path = build_annotation_json_path(folder)
+    if not os.path.exists(json_path):
+        return
+    abs_path = os.path.abspath(clip_path)
+    with open(json_path, "r", encoding="utf-8") as f:
+        try:
+            entries = json.load(f)
+        except (json.JSONDecodeError, ValueError):
+            return
+    entries = [e for e in entries if e.get("path") != abs_path]
+    with open(json_path, "w", encoding="utf-8") as f:
+        json.dump(entries, f, indent=2, ensure_ascii=False)
+        f.write("\n")
+
+
+def upsert_clip_annotation(folder: str, clip_path: str, label: str) -> None:
+    """Insert or update one entry in <folder>/dataset.json.
+
+    Each entry stores a path relative to *folder* and the sound label.
+    Matches on ``path``; if an entry for the same clip already exists it is
+    replaced (overwrite-export case).  Nothing is written when *label* is
+    empty.
+    """
+    if not label.strip():
+        return
+    os.makedirs(folder, exist_ok=True)
+    json_path = build_annotation_json_path(folder)
+    entries: list[dict] = []
+    if os.path.exists(json_path):
+        with open(json_path, "r", encoding="utf-8") as f:
+            try:
+                entries = json.load(f)
+            except (json.JSONDecodeError, ValueError):
+                entries = []
+    abs_path = os.path.abspath(clip_path)
+    entry: dict = {"path": abs_path, "label": label}
+    for i, e in enumerate(entries):
+        if e.get("path") == abs_path:
+            entries[i] = entry
+            break
+    else:
+        entries.append(entry)
+    with open(json_path, "w", encoding="utf-8") as f:
+        json.dump(entries, f, indent=2, ensure_ascii=False)
+        f.write("\n")