diff --git a/nemoguardrails/tracing/adapters/filesystem.py b/nemoguardrails/tracing/adapters/filesystem.py
index 3e99398b8..98c16bcb4 100644
--- a/nemoguardrails/tracing/adapters/filesystem.py
+++ b/nemoguardrails/tracing/adapters/filesystem.py
@@ -59,7 +59,7 @@ def transform(self, interaction_log: "InteractionLog"):
         }
 
         with open(self.filepath, "a") as f:
-            f.write(json.dumps(log_dict, indent=2) + "\n")
+            f.write(json.dumps(log_dict) + "\n")
 
     async def transform_async(self, interaction_log: "InteractionLog"):
         try:
@@ -90,4 +90,4 @@ async def transform_async(self, interaction_log: "InteractionLog"):
         }
 
         async with aiofiles.open(self.filepath, "a") as f:
-            await f.write(json.dumps(log_dict, indent=2) + "\n")
+            await f.write(json.dumps(log_dict) + "\n")
diff --git a/tests/test_tracing_adapters_filesystem.py b/tests/test_tracing_adapters_filesystem.py
index df4a470c9..a69b81f31 100644
--- a/tests/test_tracing_adapters_filesystem.py
+++ b/tests/test_tracing_adapters_filesystem.py
@@ -19,7 +19,6 @@
 import os
 import tempfile
 import unittest
-from unittest.mock import MagicMock
 
 from nemoguardrails.eval.models import Span
 from nemoguardrails.tracing import InteractionLog
@@ -109,3 +108,149 @@ async def run_test():
                 self.assertEqual(log_dict["spans"][0]["name"], "test_span")
 
         asyncio.run(run_test())
+
+    def test_jsonl_format_single_record(self):
+        """Test that output is valid JSONL format (single line per JSON object)."""
+        adapter = FileSystemAdapter(filepath=self.filepath)
+
+        interaction_log = InteractionLog(
+            id="test_id",
+            activated_rails=[],
+            events=[],
+            trace=[
+                Span(
+                    name="test_span",
+                    span_id="span_1",
+                    parent_id=None,
+                    start_time=0.0,
+                    end_time=1.0,
+                    duration=1.0,
+                    metrics={},
+                )
+            ],
+        )
+
+        adapter.transform(interaction_log)
+
+        with open(self.filepath, "r") as f:
+            lines = f.readlines()
+
+        self.assertEqual(len(lines), 1, "Should have exactly one line")
+
+        line = lines[0].strip()
+        self.assertNotEqual(line, "", "Line should not be empty")
+
+        log_dict = json.loads(line)
+        self.assertEqual(log_dict["trace_id"], "test_id")
+        self.assertEqual(len(log_dict["spans"]), 1)
+
+        self.assertNotIn("\n", line, "JSON object should not contain embedded newlines")
+
+    def test_jsonl_format_multiple_records(self):
+        """Test that multiple records create valid JSONL with one JSON per line."""
+        adapter = FileSystemAdapter(filepath=self.filepath)
+
+        log1 = InteractionLog(
+            id="trace_1",
+            activated_rails=[],
+            events=[],
+            trace=[
+                Span(
+                    name="span_1",
+                    span_id="span_1",
+                    parent_id=None,
+                    start_time=0.0,
+                    end_time=1.0,
+                    duration=1.0,
+                    metrics={"count": 1},
+                )
+            ],
+        )
+
+        log2 = InteractionLog(
+            id="trace_2",
+            activated_rails=[],
+            events=[],
+            trace=[
+                Span(
+                    name="span_2a",
+                    span_id="span_2a",
+                    parent_id=None,
+                    start_time=0.0,
+                    end_time=0.5,
+                    duration=0.5,
+                    metrics={},
+                ),
+                Span(
+                    name="span_2b",
+                    span_id="span_2b",
+                    parent_id="span_2a",
+                    start_time=0.5,
+                    end_time=1.0,
+                    duration=0.5,
+                    metrics={"score": 0.95},
+                ),
+            ],
+        )
+
+        adapter.transform(log1)
+        adapter.transform(log2)
+
+        with open(self.filepath, "r") as f:
+            lines = f.readlines()
+
+        self.assertEqual(len(lines), 2, "Should have exactly two lines")
+
+        parsed_logs = []
+        for i, line in enumerate(lines):
+            line = line.strip()
+            self.assertNotEqual(line, "", f"Line {i + 1} should not be empty")
+
+            log_dict = json.loads(line)
+            parsed_logs.append(log_dict)
+
+            self.assertNotIn(
+                "\n", line, f"Line {i + 1} should not contain embedded newlines"
+            )
+
+        self.assertEqual(parsed_logs[0]["trace_id"], "trace_1")
+        self.assertEqual(len(parsed_logs[0]["spans"]), 1)
+
+        self.assertEqual(parsed_logs[1]["trace_id"], "trace_2")
+        self.assertEqual(len(parsed_logs[1]["spans"]), 2)
+
+    def test_jsonl_streaming_compatible(self):
+        """Test that file can be processed as streaming JSONL."""
+        adapter = FileSystemAdapter(filepath=self.filepath)
+
+        for i in range(3):
+            log = InteractionLog(
+                id=f"trace_{i}",
+                activated_rails=[],
+                events=[],
+                trace=[
+                    Span(
+                        name=f"span_{i}",
+                        span_id=f"span_{i}",
+                        parent_id=None,
+                        start_time=float(i),
+                        end_time=float(i + 1),
+                        duration=1.0,
+                        metrics={"index": i},
+                    )
+                ],
+            )
+            adapter.transform(log)
+
+        trace_ids = []
+        with open(self.filepath, "r") as f:
+            for line_num, line in enumerate(f, 1):
+                if line.strip():
+                    try:
+                        record = json.loads(line)
+                        trace_ids.append(record["trace_id"])
+                    except json.JSONDecodeError as e:
+                        self.fail(f"Line {line_num} is not valid JSON: {e}")
+
+        self.assertEqual(trace_ids, ["trace_0", "trace_1", "trace_2"])
+        self.assertEqual(len(trace_ids), 3, "Should have processed 3 records")