diff --git a/blueprints/chat.py b/blueprints/chat.py
index 6e5262d..d24d0c6 100644
--- a/blueprints/chat.py
+++ b/blueprints/chat.py
@@ -63,6 +63,36 @@ def ping_llm():
         return jsonify({"status": "error", "error": str(e), "url": url, "model": model, "embed_model": embed_model}), 502
 
 
+@chat_bp.route("/debug-rag", methods=["GET"])
+@login_required
+def debug_rag():
+    """Diagnose RAG: show collection size, run a test query, return raw distances."""
+    query = request.args.get("q", "test")
+    source_id = request.args.get("source_id", type=int)
+    source_type = request.args.get("source_type", "doc")
+    try:
+        collection = rag_service._get_collection()
+        total_chunks = collection.count()
+        source_ids = [source_id] if source_id else None
+        raw = collection.query(
+            query_texts=[query],
+            n_results=min(5, max(1, total_chunks)),
+            where=rag_service._build_where(current_user.id, source_ids, source_type if source_id else None),
+            include=["documents", "distances", "ids"],
+        )
+        hits = [
+            {"id": i, "distance": round(d, 4), "preview": t[:120]}
+            for i, d, t in zip(
+                (raw.get("ids") or [[]])[0],
+                (raw.get("distances") or [[]])[0],
+                (raw.get("documents") or [[]])[0],
+            )
+        ]
+        return jsonify({"total_chunks": total_chunks, "query": query, "hits": hits})
+    except Exception as e:
+        return jsonify({"error": str(e)}), 500
+
+
 # ── Main chat ────────────────────────────────────────────────────────────────
 
 @chat_bp.route("/sessions/<int:session_id>/ask", methods=["POST"])
@@ -108,6 +138,8 @@ def ask(session_id):
     except Exception as e:
         current_app.logger.warning(f"RAG lookup failed, continuing without context: {e}")
 
+    current_app.logger.info(f"RAG: found {len(chunks)} chunks for session {session_id}")
+
     # Build history (last 10 messages for context window)
     history = [
         {"role": m.role, "content": m.content}
diff --git a/services/rag_service.py b/services/rag_service.py
index 3f2c2d9..3e3cd0e 100644
--- a/services/rag_service.py
+++ b/services/rag_service.py
@@ -190,6 +190,16 @@ def _fetch_neighbor_docs(chunk_id: str, collection) -> list[tuple[str, str]]:
     return neighbors
 
 
+def _build_where(user_id: int, source_ids=None, source_type=None) -> dict:
+    """Build a ChromaDB where-filter for user/source scoping."""
+    conditions = [{"user_id": {"$eq": str(user_id)}}]
+    if source_ids is not None and len(source_ids) > 0:
+        conditions.append({"source_id": {"$in": [str(sid) for sid in source_ids]}})
+    if source_type:
+        conditions.append({"source_type": {"$eq": source_type}})
+    return {"$and": conditions} if len(conditions) > 1 else conditions[0]
+
+
 def similarity_search(
     query: str,
     user_id: int,
@@ -199,13 +209,7 @@ def similarity_search(
 ) -> list[str]:
     """Multi-query search with neighbor expansion and reading-order sorting."""
     collection = _get_collection()
-
-    conditions = [{"user_id": {"$eq": str(user_id)}}]
-    if source_ids is not None and len(source_ids) > 0:
-        conditions.append({"source_id": {"$in": [str(sid) for sid in source_ids]}})
-    if source_type:
-        conditions.append({"source_type": {"$eq": source_type}})
-    where = {"$and": conditions} if len(conditions) > 1 else conditions[0]
+    where = _build_where(user_id, source_ids, source_type)
 
     # Generate multiple queries for broader recall
     queries = _expand_query(query)
@@ -228,7 +232,7 @@ def similarity_search(
             dists = (results.get("distances") or [[]])[0]
             ids = (results.get("ids") or [[]])[0]
             for doc, dist, doc_id in zip(docs, dists, ids):
-                if doc_id not in seen_ids and dist < 0.65:
+                if doc_id not in seen_ids and dist < 0.80:
                     seen_ids.add(doc_id)
                     ranked.append((dist, doc_id, doc))
         except Exception: