diff --git a/README.md b/README.md
index d87c24b..ff84d40 100644
--- a/README.md
+++ b/README.md
@@ -127,3 +127,7 @@ color-coded (green up, red down). Reconnection is handled by HTMX.
 Python · FastAPI · Uvicorn · websockets · HTMX · Tailwind CSS v4
 
 The Clojure implementation this replaced is on the `clojure` branch.
+
+The 24-hour chart uses 48 half-hour candles from rustbtcdata’s
+`/api/kraken-half-hour` endpoint, aggregated from minute OHLC data. It refreshes
+every five minutes and includes the current partial half-hour candle.
diff --git a/app/main.py b/app/main.py
index 84919b2..6278ed2 100644
--- a/app/main.py
+++ b/app/main.py
@@ -73,7 +73,7 @@ HOME_HTML = """\
 </div>
 <div class="mt-4">
 <div class="bg-white rounded-2xl shadow-sm border border-gray-200 p-6">
-<p class="text-sm text-gray-500 mb-3">24h Candles (1h)</p>
+<p class="text-sm text-gray-500 mb-3">24h Candles (30m)</p>
 <div id="chart-hour" style="height:300px"></div>
 </div>
 </div>
@@ -170,7 +170,7 @@ HOME_HTML = """\
   }
 
   initChart('chart-minute', '/api/kraken-minute', 60 * 1000);
-  initChart('chart-hour', '/api/kraken-hour', 5 * 60 * 1000, updateMidnightPrice);
+  initChart('chart-hour', '/api/kraken-half-hour', 5 * 60 * 1000, updateMidnightPrice);
 })();
 </script>
 </body>
@@ -233,6 +233,11 @@ async def _proxy_btcdata_json(path: str) -> JSONResponse:
         )
 
 
+@app.get("/api/kraken-half-hour")
+async def kraken_half_hour():
+    return await _proxy_btcdata_json("/api/kraken-half-hour")
+
+
 @app.get("/api/kraken-hour")
 async def kraken_hour():
     return await _proxy_btcdata_json("/api/kraken-hour")
diff --git a/tests/test_health.py b/tests/test_health.py
index 6c68a3c..67ee1b4 100644
--- a/tests/test_health.py
+++ b/tests/test_health.py
@@ -107,3 +107,22 @@ def test_version_endpoint(monkeypatch):
 
     assert response.status_code == 200
     assert response.json() == {"version": "abc1234"}
+
+
+def test_24_hour_chart_uses_half_hour_candles():
+    response = TestClient(main.app).get("/")
+    assert "24h Candles (30m)" in response.text
+    assert "initChart('chart-hour', '/api/kraken-half-hour', 5 * 60 * 1000, updateMidnightPrice)" in response.text
+    assert "initChart('chart-minute', '/api/kraken-minute', 60 * 1000)" in response.text
+
+
+def test_half_hour_proxy_preserves_candles_and_upstream_errors(monkeypatch):
+    for status, payload in [(200, [{"ts": 1800, "open": "10", "high": "12", "low": "9", "close": "11"}]), (503, {"error": "database unavailable"})]:
+        request = httpx.Request("GET", "http://btcdata.test/api/kraken-half-hour")
+        client = StubAsyncClient(response=httpx.Response(status, json=payload, request=request))
+        monkeypatch.setattr(main, "BTCDATA_URL", "http://btcdata.test")
+        monkeypatch.setattr(main.httpx, "AsyncClient", lambda: client)
+        response = TestClient(main.app).get("/api/kraken-half-hour")
+        assert response.status_code == status
+        assert response.json() == payload
+        assert client.requested_url == "http://btcdata.test/api/kraken-half-hour"