diff --git a/graphiti_core/prompts/dedupe_edges.py b/graphiti_core/prompts/dedupe_edges.py
index bfc46a6fb6..f20895affc 100644
--- a/graphiti_core/prompts/dedupe_edges.py
+++ b/graphiti_core/prompts/dedupe_edges.py
@@ -22,6 +22,13 @@
 
 
 class EdgeDuplicate(BaseModel):
+    reasoning: str = Field(
+        default='',
+        description=(
+            'Briefly reason about duplicates and contradictions before the final arrays. '
+            'For every selected fact, cite its continuous idx number.'
+        ),
+    )
     duplicate_facts: list[int] = Field(
         ...,
         description='List of idx values of duplicate facts (only from EXISTING FACTS range). Empty list if none.',
@@ -82,6 +89,11 @@ def resolve_edge(context: dict[str, Any]) -> list[Message]:
    - Return all contradicted idx values in contradicted_facts.
    - If no contradictions, return an empty list for contradicted_facts.
 
+Before returning the arrays, explain your decision in a short reasoning field. '
+For every duplicate or contradiction, explicitly cite its idx number in the reasoning '
+(for example, "idx 2 is contradicted because the value changed"). Then return the '
+duplicate_facts and contradicted_facts arrays using those same idx values.
+
 <EXAMPLE>
 EXISTING FACT: idx=0, "Alice joined Acme Corp in 2020"
 NEW FACT: "Alice joined Acme Corp in 2020"
diff --git a/tests/prompts/test_dedupe_edges.py b/tests/prompts/test_dedupe_edges.py
new file mode 100644
index 0000000000..1c5ee10c0b
--- /dev/null
+++ b/tests/prompts/test_dedupe_edges.py
@@ -0,0 +1,25 @@
+from graphiti_core.prompts.dedupe_edges import EdgeDuplicate, resolve_edge
+
+
+def test_edge_duplicate_schema_collects_reasoning_before_indices():
+    fields = list(EdgeDuplicate.model_fields)
+
+    assert fields[:3] == ['reasoning', 'duplicate_facts', 'contradicted_facts']
+    assert EdgeDuplicate(
+        reasoning='idx 1 contradicts the new fact',
+        duplicate_facts=[],
+        contradicted_facts=[1],
+    ).contradicted_facts == [1]
+
+
+def test_resolve_edge_prompt_requires_index_reasoning_first():
+    prompt = resolve_edge(
+        {
+            'existing_edges': [{'idx': 0, 'fact': 'A'}],
+            'edge_invalidation_candidates': [{'idx': 1, 'fact': 'B'}],
+            'new_edge': 'C',
+        }
+    )[-1].content
+
+    assert 'reasoning' in prompt.lower()
+    assert 'idx number' in prompt.lower()