diff --git a/motion/operations/gather.py b/motion/operations/gather.py
index a6df9464..ad181e0a 100644
--- a/motion/operations/gather.py
+++ b/motion/operations/gather.py
@@ -84,7 +84,7 @@ def execute(self, input_data: List[Dict]) -> Tuple[List[Dict], float]:
             "main_chunk_start", "--- Begin Main Chunk ---"
         )
         main_chunk_end = self.config.get("main_chunk_end", "--- End Main Chunk ---")
-        doc_header_keys = self.config.get("doc_header_keys", [])
+        doc_header_key = self.config.get("doc_header_key", None)
         results = []
         cost = 0.0
 
@@ -111,7 +111,7 @@ def execute(self, input_data: List[Dict]) -> Tuple[List[Dict], float]:
                     order_key,
                     main_chunk_start,
                     main_chunk_end,
-                    doc_header_keys,
+                    doc_header_key,
                 )
 
                 result = chunk.copy()
@@ -129,7 +129,7 @@ def render_chunk_with_context(
         order_key: str,
         main_chunk_start: str,
         main_chunk_end: str,
-        doc_header_keys: List[Dict[str, Any]],
+        doc_header_key: str,
     ) -> str:
         """
         Render a chunk with its peripheral context and headers.
@@ -142,7 +142,7 @@ def render_chunk_with_context(
             order_key (str): Key for the order of each chunk.
             main_chunk_start (str): String to mark the start of the main chunk.
             main_chunk_end (str): String to mark the end of the main chunk.
-            doc_header_keys (List[Dict[str, Any]]): List of dicts containing 'header' and 'level' keys.
+            doc_header_key (str): The key for the headers in the current chunk.
 
         Returns:
             str: Renderted chunk with context and headers.
@@ -164,7 +164,7 @@ def render_chunk_with_context(
         # Process main chunk
         main_chunk = chunks[current_index]
         headers = self.render_hierarchy_headers(
-            main_chunk, chunks[: current_index + 1], doc_header_keys
+            main_chunk, chunks[: current_index + 1], doc_header_key
         )
         if headers:
             combined_parts.append(headers)
@@ -270,7 +270,7 @@ def render_hierarchy_headers(
         self,
         current_chunk: Dict,
         chunks: List[Dict],
-        doc_header_keys: List[Dict[str, Any]],
+        doc_header_key: str,
     ) -> str:
         """
         Render headers for the current chunk's hierarchy.
@@ -278,16 +278,18 @@ def render_hierarchy_headers(
         Args:
             current_chunk (Dict): The current chunk being processed.
             chunks (List[Dict]): List of chunks up to and including the current chunk.
-            doc_header_keys (List[Dict[str, Any]]): List of dicts containing 'header' and 'level' keys.
-
+            doc_header_key (str): The key for the headers in the current chunk.
         Returns:
             str: Renderted headers in the current chunk's hierarchy.
         """
         rendered_headers = []
         current_hierarchy = {}
 
+        if doc_header_key is None:
+            return ""
+
         # Find the largest/highest level in the current chunk
-        current_chunk_headers = current_chunk.get(doc_header_keys, [])
+        current_chunk_headers = current_chunk.get(doc_header_key, [])
         highest_level = float("inf")  # Initialize with positive infinity
         for header_info in current_chunk_headers:
             level = header_info.get("level")
@@ -299,7 +301,7 @@ def render_hierarchy_headers(
             highest_level = None
 
         for chunk in chunks:
-            for header_info in chunk.get(doc_header_keys, []):
+            for header_info in chunk.get(doc_header_key, []):
                 header = header_info["header"]
                 level = header_info["level"]
                 if header and level:
diff --git a/motion/optimizers/map_optimizer/operation_creators.py b/motion/optimizers/map_optimizer/operation_creators.py
index 3823947e..362b5005 100644
--- a/motion/optimizers/map_optimizer/operation_creators.py
+++ b/motion/optimizers/map_optimizer/operation_creators.py
@@ -120,7 +120,7 @@ def create_split_map_gather_operations(
             "content_key": content_key,
             "doc_id_key": f"{split_name}_id",
             "order_key": f"{split_name}_chunk_num",
-            "doc_header_keys": ("headers" if header_output_schema else []),
+            "doc_header_key": "headers" if header_output_schema else [],
             "peripheral_chunks": {},
         }
 
diff --git a/tests/test_synth_gather.py b/tests/test_synth_gather.py
index 9e34bce3..1fa350d1 100644
--- a/tests/test_synth_gather.py
+++ b/tests/test_synth_gather.py
@@ -119,7 +119,7 @@ def test_synth_gather(config_yaml):
                 assert "doc_id_key" in synthesized_op
                 assert "order_key" in synthesized_op
                 assert "peripheral_chunks" in synthesized_op
-                assert "doc_header_keys" in synthesized_op
+                assert "doc_header_key" in synthesized_op
 
                 break
         if synthesized_gather_found:
@@ -204,7 +204,7 @@ def test_split_map_gather(sample_data):
             "previous": {"tail": {"count": 1}},
             "next": {"head": {"count": 1}},
         },
-        "doc_header_keys": "headers",
+        "doc_header_key": "headers",
     }
 
     # Initialize operations
diff --git a/todos.md b/todos.md
index cddcba6f..939f1593 100644
--- a/todos.md
+++ b/todos.md
@@ -64,6 +64,8 @@ TODO:
     - [x] Encode this in API somehow
     - [ ] Support this kind of chunking in the optimizer
   - [x] Extract headers & levels from documents, and add the level hierarchy to the chunk.
+- [ ] Support tool use in operations
+- [ ] Fix DSL to handle inputs like we've done in the Overleaf writeup
 - [ ] Support prompts exceeding context windows; figure out how to throw out data / prioritize elements
 - [ ] Support retries in the optimizers
 - [ ] Write tests for optimizers