diff --git a/backend/tests/test_api.py b/backend/tests/test_api.py
new file mode 100644
index 0000000..94ad060
--- /dev/null
+++ b/backend/tests/test_api.py
@@ -0,0 +1,373 @@
+"""Tests for FastAPI REST API endpoints."""
+
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+from datetime import datetime
+from unittest.mock import MagicMock, AsyncMock, patch
+
+from backend.app.models import RecorderConfig, PortStatus, SCTE35Marker, CodecType
+from backend.app.recorders.recorder import RecorderManager
+from backend.app.recorders.scte35 import SCTE35Manager
+from backend.app.api.routes import router
+from backend.app.api import routes as routes_module
+
+
+@pytest.fixture
+def app():
+    """Create test FastAPI app with mocked managers."""
+    test_app = FastAPI()
+    test_app.include_router(router)
+    return test_app
+
+
+@pytest.fixture
+def client(app):
+    """Create TestClient for the app."""
+    return TestClient(app)
+
+
+@pytest.fixture
+def mock_recorder_manager():
+    """Create a mock RecorderManager."""
+    manager = MagicMock(spec=RecorderManager)
+    
+    # Mock default status for all ports
+    port_statuses = [
+        PortStatus(
+            port_index=i,
+            is_recording=False,
+            frame_count=0,
+            fps=0.0,
+            bitrate_mbps=0.0,
+            uptime_seconds=0,
+            current_file="/recordings/port_{}.ts".format(i),
+            codec=CodecType.H264,
+        )
+        for i in range(4)
+    ]
+    
+    manager.get_all_status.return_value = port_statuses
+    manager.get_status.return_value = port_statuses[0]
+    manager.start_recording = AsyncMock()
+    manager.stop_recording = AsyncMock()
+    
+    return manager
+
+
+@pytest.fixture
+def mock_scte35_manager():
+    """Create a mock SCTE35Manager."""
+    manager = MagicMock(spec=SCTE35Manager)
+    manager.inject_marker = AsyncMock()
+    manager.get_marker_history.return_value = []
+    return manager
+
+
+@pytest.fixture(autouse=True)
+def inject_managers(mock_recorder_manager, mock_scte35_manager):
+    """Inject mocked managers into routes module."""
+    routes_module.recorder_manager = mock_recorder_manager
+    routes_module.scte35_manager = mock_scte35_manager
+    yield
+    # Clean up
+    routes_module.recorder_manager = None
+    routes_module.scte35_manager = None
+
+
+def test_health_endpoint_returns_ok(client):
+    """GET /api/health returns 200 with status=ok"""
+    response = client.get("/api/health")
+    assert response.status_code == 200
+    data = response.json()
+    assert data["status"] == "ok"
+    assert "ports" in data
+    assert "recording_count" in data
+
+
+def test_get_all_ports_returns_list(client, mock_recorder_manager):
+    """GET /api/ports returns list of port statuses"""
+    response = client.get("/api/ports")
+    assert response.status_code == 200
+    data = response.json()
+    assert isinstance(data, list)
+    assert len(data) == 4
+    assert all("port_index" in port for port in data)
+    assert all("is_recording" in port for port in data)
+
+
+def test_get_port_by_index(client, mock_recorder_manager):
+    """GET /api/ports/0 returns single port status"""
+    response = client.get("/api/ports/0")
+    assert response.status_code == 200
+    data = response.json()
+    assert data["port_index"] == 0
+    assert "is_recording" in data
+
+
+def test_get_port_not_found(client, mock_recorder_manager):
+    """GET /api/ports/999 returns 404"""
+    mock_recorder_manager.get_status.side_effect = ValueError("Invalid port")
+    response = client.get("/api/ports/999")
+    assert response.status_code == 404
+
+
+def test_start_recording(client, mock_recorder_manager):
+    """POST /api/ports/0/start returns 200 and starts recording"""
+    config = {
+        "port_index": 0,
+        "codec": "h264",
+        "bitrate": 50,
+        "quality_profile": "high",
+        "recording_path": "/recordings/test.ts",
+        "srt_enabled": False,
+    }
+    
+    response = client.post("/api/ports/0/start", json=config)
+    assert response.status_code == 200
+    data = response.json()
+    assert data["message"] == "Recording started"
+    assert data["port"] == 0
+    
+    # Verify start_recording was called
+    mock_recorder_manager.start_recording.assert_called_once()
+
+
+def test_start_recording_already_running(client, mock_recorder_manager):
+    """POST /api/ports/0/start returns 400 if already recording"""
+    mock_recorder_manager.start_recording.side_effect = RuntimeError("Already recording")
+    
+    config = {
+        "port_index": 0,
+        "codec": "h264",
+        "bitrate": 50,
+        "quality_profile": "high",
+        "recording_path": "/recordings/test.ts",
+        "srt_enabled": False,
+    }
+    
+    response = client.post("/api/ports/0/start", json=config)
+    assert response.status_code == 400
+
+
+def test_start_recording_invalid_port(client, mock_recorder_manager):
+    """POST /api/ports/999/start returns 404"""
+    mock_recorder_manager.start_recording.side_effect = ValueError("Invalid port")
+    
+    config = {
+        "port_index": 999,
+        "codec": "h264",
+        "bitrate": 50,
+        "quality_profile": "high",
+        "recording_path": "/recordings/test.ts",
+        "srt_enabled": False,
+    }
+    
+    response = client.post("/api/ports/999/start", json=config)
+    assert response.status_code == 404
+
+
+def test_stop_recording(client, mock_recorder_manager):
+    """POST /api/ports/0/stop returns 200 and stops recording"""
+    response = client.post("/api/ports/0/stop")
+    assert response.status_code == 200
+    data = response.json()
+    assert data["message"] == "Recording stopped"
+    assert data["port"] == 0
+    
+    # Verify stop_recording was called
+    mock_recorder_manager.stop_recording.assert_called_once()
+
+
+def test_stop_recording_invalid_port(client, mock_recorder_manager):
+    """POST /api/ports/999/stop returns 404"""
+    mock_recorder_manager.stop_recording.side_effect = ValueError("Invalid port")
+    response = client.post("/api/ports/999/stop")
+    assert response.status_code == 404
+
+
+def test_inject_scte35_marker(client, mock_scte35_manager):
+    """POST /api/scte35/inject returns SCTE35Marker"""
+    marker_response = SCTE35Marker(
+        event_id="12345",
+        duration_seconds=30,
+        out_of_network=True,
+        splice_immediate=False,
+        timestamp=datetime.utcnow(),
+        webhook_url=None,
+    )
+    mock_scte35_manager.inject_marker.return_value = marker_response
+    
+    payload = {
+        "event_id": 12345,
+        "duration_seconds": 30.0,
+        "webhook_url": None,
+        "out_of_network": True,
+        "splice_immediate": False,
+    }
+    
+    response = client.post("/api/scte35/inject", json=payload)
+    assert response.status_code == 200
+    data = response.json()
+    assert data["event_id"] == "12345"
+    assert data["duration_seconds"] == 30
+    
+    # Verify inject_marker was called
+    mock_scte35_manager.inject_marker.assert_called_once()
+
+
+def test_inject_scte35_with_invalid_event_id(client, mock_scte35_manager):
+    """POST /api/scte35/inject returns 400 for invalid event_id"""
+    mock_scte35_manager.inject_marker.side_effect = ValueError("Invalid event_id")
+    
+    payload = {
+        "event_id": -1,
+        "duration_seconds": 30.0,
+        "webhook_url": None,
+        "out_of_network": True,
+        "splice_immediate": False,
+    }
+    
+    response = client.post("/api/scte35/inject", json=payload)
+    assert response.status_code == 400
+
+
+def test_get_scte35_history(client, mock_scte35_manager):
+    """GET /api/scte35/history returns list of markers"""
+    marker = SCTE35Marker(
+        event_id="12345",
+        duration_seconds=30,
+        out_of_network=True,
+        splice_immediate=False,
+        timestamp=datetime.utcnow(),
+        webhook_url=None,
+    )
+    mock_scte35_manager.get_marker_history.return_value = [marker]
+    
+    response = client.get("/api/scte35/history")
+    assert response.status_code == 200
+    data = response.json()
+    assert isinstance(data, list)
+    assert len(data) == 1
+    assert data[0]["event_id"] == "12345"
+
+
+# ============================================================================
+# WebSocket Manager Tests
+# ============================================================================
+
+from fastapi import WebSocket
+from backend.app.api.websocket import ConnectionManager
+
+
+@pytest.mark.asyncio
+async def test_websocket_connection_manager_init():
+    """ConnectionManager initializes with empty connections list"""
+    manager = ConnectionManager()
+    assert manager.active_connections == []
+
+
+@pytest.mark.asyncio
+async def test_websocket_connect():
+    """ConnectionManager can connect a WebSocket"""
+    manager = ConnectionManager()
+    
+    # Mock WebSocket
+    ws = AsyncMock(spec=WebSocket)
+    ws.accept = AsyncMock()
+    
+    await manager.connect(ws)
+    assert ws in manager.active_connections
+    ws.accept.assert_called_once()
+
+
+@pytest.mark.asyncio
+async def test_websocket_disconnect():
+    """ConnectionManager can disconnect a WebSocket"""
+    manager = ConnectionManager()
+    
+    ws = AsyncMock(spec=WebSocket)
+    ws.accept = AsyncMock()
+    
+    await manager.connect(ws)
+    assert ws in manager.active_connections
+    
+    manager.disconnect(ws)
+    assert ws not in manager.active_connections
+
+
+@pytest.mark.asyncio
+async def test_websocket_broadcast():
+    """ConnectionManager broadcasts to all connections"""
+    manager = ConnectionManager()
+    
+    ws1 = AsyncMock(spec=WebSocket)
+    ws2 = AsyncMock(spec=WebSocket)
+    ws1.accept = AsyncMock()
+    ws2.accept = AsyncMock()
+    ws1.send_json = AsyncMock()
+    ws2.send_json = AsyncMock()
+    
+    await manager.connect(ws1)
+    await manager.connect(ws2)
+    
+    data = {"status": "ok", "ports": 4}
+    await manager.broadcast(data)
+    
+    ws1.send_json.assert_called_once_with(data)
+    ws2.send_json.assert_called_once_with(data)
+
+
+@pytest.mark.asyncio
+async def test_websocket_broadcast_removes_dead_connections():
+    """ConnectionManager removes connections that fail to send"""
+    manager = ConnectionManager()
+    
+    ws_good = AsyncMock(spec=WebSocket)
+    ws_bad = AsyncMock(spec=WebSocket)
+    ws_good.accept = AsyncMock()
+    ws_bad.accept = AsyncMock()
+    ws_good.send_json = AsyncMock()
+    ws_bad.send_json = AsyncMock(side_effect=Exception("Connection closed"))
+    
+    await manager.connect(ws_good)
+    await manager.connect(ws_bad)
+    
+    assert len(manager.active_connections) == 2
+    
+    data = {"status": "ok"}
+    await manager.broadcast(data)
+    
+    # Dead connection should be removed
+    assert len(manager.active_connections) == 1
+    assert ws_good in manager.active_connections
+    assert ws_bad not in manager.active_connections
+
+
+@pytest.mark.asyncio
+async def test_websocket_send_personal_message():
+    """ConnectionManager can send personal message"""
+    manager = ConnectionManager()
+    
+    ws = AsyncMock(spec=WebSocket)
+    ws.send_text = AsyncMock()
+    
+    await manager.send_personal_message("Hello", ws)
+    ws.send_text.assert_called_once_with("Hello")
+
+
+@pytest.mark.asyncio
+async def test_websocket_send_personal_message_removes_bad_connection():
+    """ConnectionManager removes connection on failed personal message"""
+    manager = ConnectionManager()
+    
+    ws = AsyncMock(spec=WebSocket)
+    ws.send_text = AsyncMock(side_effect=Exception("Connection closed"))
+    
+    await manager.connect(ws)
+    assert ws in manager.active_connections
+    
+    await manager.send_personal_message("Hello", ws)
+    
+    # Should be removed after failed send
+    assert ws not in manager.active_connections