diff --git a/tests/integration/guardrails/test_header_guardrails.py b/tests/integration/guardrails/test_header_guardrails.py
new file mode 100644
index 0000000..d5d6231
--- /dev/null
+++ b/tests/integration/guardrails/test_header_guardrails.py
@@ -0,0 +1,186 @@
+"""Test the guardrails from file with the OpenAI route."""
+
+import os
+import sys
+import uuid
+import time
+
+# Add integration folder (parent) to sys.path
+sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+import pytest
+import requests
+from httpx import Client
+from openai import OpenAI, BadRequestError, APIError
+
+# Pytest plugins
+pytest_plugins = ("pytest_asyncio",)
+
+
+@pytest.mark.skipif(not os.getenv("OPENAI_API_KEY"), reason="No OPENAI_API_KEY set")
+@pytest.mark.parametrize(
+    "do_stream, push_to_explorer",
+    [(True, True), (True, False), (False, True), (False, False)],
+)
+async def test_input_guardrail_in_header(
+    explorer_api_url, gateway_url, do_stream, push_to_explorer
+):
+    """Test the message content guardrail."""
+    if not os.getenv("INVARIANT_API_KEY"):
+        pytest.fail("No INVARIANT_API_KEY set, failing")
+
+    dataset_name = f"test-dataset-open-ai-{uuid.uuid4()}"
+
+    policy = """
+# For input guardrailing specifically
+raise "Users must not mention the magic phrase 'Abracadabra'" if:
+    (msg: Message)
+    msg.role == "user"
+    "Abracadabra" in msg.content
+"""
+
+    client = OpenAI(
+        http_client=Client(
+            headers={
+                "Invariant-Authorization": f"Bearer {os.getenv('INVARIANT_API_KEY')}",
+                "Invariant-Guardrails": policy.encode("unicode-escape"),
+            },
+        ),
+        base_url=f"{gateway_url}/api/v1/gateway/{dataset_name}/openai"
+        if push_to_explorer
+        else f"{gateway_url}/api/v1/gateway/openai",
+    )
+
+    request = {
+        "model": "gpt-4o",
+        "messages": [{"role": "user", "content": "Tell me more about Abracadabra."}],
+    }
+
+    if not do_stream:
+        with pytest.raises(BadRequestError) as exc_info:
+            chat_response = client.chat.completions.create(
+                **request,
+                stream=False,
+            )
+
+        assert exc_info.value.status_code == 400
+        assert "[Invariant] The request did not pass the guardrails" in str(
+            exc_info.value
+        )
+        assert "Users must not mention the magic phrase 'Abracadabra'" in str(
+            exc_info.value
+        )
+
+    else:
+        with pytest.raises(APIError) as exc_info:
+            chat_response = client.chat.completions.create(
+                **request,
+                stream=True,
+            )
+
+            for _ in chat_response:
+                pass
+        assert (
+            "[Invariant] The request did not pass the guardrails"
+            in exc_info.value.message
+        )
+        assert "Users must not mention the magic phrase 'Abracadabra'" in str(
+            exc_info.value.body
+        )
+
+    if push_to_explorer:
+        # Wait for the trace to be saved
+        # This is needed because the trace is saved asynchronously
+        time.sleep(2)
+
+        # Fetch the trace ids for the dataset
+        traces_response = requests.get(
+            f"{explorer_api_url}/api/v1/dataset/byuser/developer/{dataset_name}/traces",
+            timeout=5,
+        )
+        traces = traces_response.json()
+        assert len(traces) == 1
+        trace_id = traces[0]["id"]
+
+        # Fetch the trace
+        trace_response = requests.get(
+            f"{explorer_api_url}/api/v1/trace/{trace_id}",
+            timeout=5,
+        )
+        trace = trace_response.json()
+
+        # in case of input guardrailing, the pushed trace will not contain a response
+        assert len(trace["messages"]) == 1
+        assert trace["messages"][0] == {
+            "role": "user",
+            "content": "Tell me more about Abracadabra.",
+        }
+
+        # Fetch annotations
+        annotations_response = requests.get(
+            f"{explorer_api_url}/api/v1/trace/{trace_id}/annotations",
+            timeout=5,
+        )
+        annotations = annotations_response.json()
+
+        assert len(annotations) == 1
+        assert (
+            annotations[0]["content"]
+            == "Users must not mention the magic phrase 'Abracadabra'"
+            and annotations[0]["extra_metadata"]["source"] == "guardrails-error"
+        )
+
+
+@pytest.mark.skipif(not os.getenv("OPENAI_API_KEY"), reason="No OPENAI_API_KEY set")
+@pytest.mark.parametrize(
+    "do_stream, push_to_explorer",
+    [(True, True), (True, False), (False, True), (False, False)],
+)
+async def test_invalid_guardrail_in_header(
+    explorer_api_url, gateway_url, do_stream, push_to_explorer
+):
+    """Test the message content guardrail."""
+    if not os.getenv("INVARIANT_API_KEY"):
+        pytest.fail("No INVARIANT_API_KEY set, failing")
+
+    dataset_name = f"test-dataset-open-ai-{uuid.uuid4()}"
+
+    policy = """
+# For input guardrailing specifically
+raise "Users must not mention the magic phrase 'Abracadabra'" if:
+    (msg: Message)
+    msg.role == "user"
+    "Abracadabra" in msg.content
+    illegal statement
+"""
+
+    client = OpenAI(
+        http_client=Client(
+            headers={
+                "Invariant-Authorization": f"Bearer {os.getenv('INVARIANT_API_KEY')}",
+                "Invariant-Guardrails": policy.encode("unicode-escape"),
+            },
+        ),
+        base_url=f"{gateway_url}/api/v1/gateway/{dataset_name}/openai"
+        if push_to_explorer
+        else f"{gateway_url}/api/v1/gateway/openai",
+    )
+
+    request = {
+        "model": "gpt-4o",
+        "messages": [{"role": "user", "content": "Tell me more about Abracadabra."}],
+    }
+
+    if not do_stream:
+        with pytest.raises(BadRequestError) as exc_info:
+            chat_response = client.chat.completions.create(
+                **request,
+                stream=False,
+            )
+
+        assert "Gateway: Guardrails check failed" in str(
+            exc_info.value
+        ), "guardrails check fails because of an invalid guardrailing rule"
+        assert "illegal statement" in str(
+            exc_info.value
+        ), "error points to illegal statement in the rule definition"