diff --git a/hbd/server/http.py b/hbd/server/http.py
index bf5e7c6..762381d 100644
--- a/hbd/server/http.py
+++ b/hbd/server/http.py
@@ -126,6 +126,46 @@ def _mask_config_for_api(config) -> dict:
     return result
 
 
+def _build_host_info(host, threshold_checker=None) -> dict:
+    """Assemble the info payload for GET /api/0/hosts/{hostname}/info."""
+    hbc_version = None
+    hbc_type = None
+    latest_os = host.get_latest_plugin_data("os_info")
+    if latest_os:
+        _, os_data = latest_os
+        hbc_version = os_data.get("hbc_version")
+        hbc_type = os_data.get("hbc_type")
+
+    last_packet = None
+    if host.connections:
+        last_packet = max(conn.lastbeat for conn in host.connections.values())
+
+    thresholds = None
+    if threshold_checker is not None:
+        raw = threshold_checker.get_thresholds_for_host(host.name)
+        thresholds = sorted(
+            [
+                {
+                    "metric": tc.metric_path,
+                    "warning": tc.warning,
+                    "critical": tc.critical,
+                    "operator": tc.operator.value,
+                }
+                for tc in raw.values()
+            ],
+            key=lambda x: x["metric"],
+        )
+
+    return {
+        "owner": getattr(host, "owner", None),
+        "managers": list(getattr(host, "managers", [])),
+        "hbc_version": hbc_version,
+        "hbc_type": hbc_type,
+        "last_packet": last_packet,
+        "thresholds": thresholds,
+    }
+
+
 async def start(
     host: str,
     port: int,
diff --git a/tests/test_http_host_info.py b/tests/test_http_host_info.py
new file mode 100644
index 0000000..39b2171
--- /dev/null
+++ b/tests/test_http_host_info.py
@@ -0,0 +1,129 @@
+"""Tests for _build_host_info helper in http.py."""
+import pytest
+from unittest.mock import MagicMock
+from hbd.server.http import _build_host_info
+
+
+class _FakeConn:
+    def __init__(self, lastbeat):
+        self.lastbeat = lastbeat
+
+
+class _FakeHost:
+    def __init__(self, name="myhost", owner=None, managers=None,
+                 connections=None, os_data=None):
+        self.name = name
+        self.owner = owner
+        self.managers = managers or []
+        self.connections = connections or {}
+        self._os_data = os_data
+
+    def get_latest_plugin_data(self, plugin_name):
+        if plugin_name == "os_info" and self._os_data is not None:
+            return (1234567890.0, self._os_data)
+        return None
+
+
+def test_build_host_info_basic_fields():
+    host = _FakeHost(owner="alice", managers=["bob", "carol"])
+    result = _build_host_info(host)
+    assert result["owner"] == "alice"
+    assert result["managers"] == ["bob", "carol"]
+    assert result["hbc_version"] is None
+    assert result["hbc_type"] is None
+    assert result["last_packet"] is None
+    assert result["thresholds"] is None
+
+
+def test_build_host_info_no_owner():
+    host = _FakeHost()
+    result = _build_host_info(host)
+    assert result["owner"] is None
+    assert result["managers"] == []
+
+
+def test_build_host_info_reads_hbc_from_os_info():
+    host = _FakeHost(os_data={"hbc_version": "5.3.0", "hbc_type": "full"})
+    result = _build_host_info(host)
+    assert result["hbc_version"] == "5.3.0"
+    assert result["hbc_type"] == "full"
+
+
+def test_build_host_info_hbc_none_when_no_os_info():
+    host = _FakeHost(os_data=None)
+    result = _build_host_info(host)
+    assert result["hbc_version"] is None
+    assert result["hbc_type"] is None
+
+
+def test_build_host_info_last_packet_is_max_lastbeat():
+    host = _FakeHost(connections={
+        "IPv4": _FakeConn(1000.0),
+        "IPv6": _FakeConn(2000.0),
+    })
+    result = _build_host_info(host)
+    assert result["last_packet"] == 2000.0
+
+
+def test_build_host_info_last_packet_none_when_no_connections():
+    host = _FakeHost(connections={})
+    result = _build_host_info(host)
+    assert result["last_packet"] is None
+
+
+def test_build_host_info_thresholds_none_without_checker():
+    host = _FakeHost()
+    result = _build_host_info(host, threshold_checker=None)
+    assert result["thresholds"] is None
+
+
+def test_build_host_info_thresholds_sorted_by_metric():
+    from hbd.server.threshold import ThresholdConfig
+    tc_cpu = ThresholdConfig("cpu_monitor.cpu_percent", warning=80.0, critical=95.0)
+    tc_mem = ThresholdConfig("memory_monitor.memory_percent", warning=85.0, critical=98.0)
+
+    checker = MagicMock()
+    checker.get_thresholds_for_host.return_value = {
+        "memory_monitor.memory_percent": tc_mem,
+        "cpu_monitor.cpu_percent": tc_cpu,
+    }
+
+    host = _FakeHost()
+    result = _build_host_info(host, threshold_checker=checker)
+
+    assert result["thresholds"] is not None
+    assert len(result["thresholds"]) == 2
+    assert result["thresholds"][0]["metric"] == "cpu_monitor.cpu_percent"
+    assert result["thresholds"][0]["warning"] == 80.0
+    assert result["thresholds"][0]["critical"] == 95.0
+    assert result["thresholds"][0]["operator"] == ">"
+    assert result["thresholds"][1]["metric"] == "memory_monitor.memory_percent"
+
+
+def test_build_host_info_thresholds_empty_list_when_no_thresholds():
+    checker = MagicMock()
+    checker.get_thresholds_for_host.return_value = {}
+    host = _FakeHost()
+    result = _build_host_info(host, threshold_checker=checker)
+    assert result["thresholds"] == []
+
+
+def test_build_host_info_threshold_null_warning_critical():
+    from hbd.server.threshold import ThresholdConfig
+    tc = ThresholdConfig("rtt.myhost", warning=None, critical=500.0)
+    checker = MagicMock()
+    checker.get_thresholds_for_host.return_value = {"rtt.myhost": tc}
+    host = _FakeHost()
+    result = _build_host_info(host, threshold_checker=checker)
+    assert result["thresholds"][0]["warning"] is None
+    assert result["thresholds"][0]["critical"] == 500.0
+
+
+def test_build_host_info_nagios_operator_serialized():
+    from hbd.server.threshold import ThresholdConfig
+    tc = ThresholdConfig("nagios_runner.check_http", operator="nagios")
+    checker = MagicMock()
+    checker.get_thresholds_for_host.return_value = {"nagios_runner.check_http": tc}
+    host = _FakeHost()
+    result = _build_host_info(host, threshold_checker=checker)
+    assert result["thresholds"][0]["operator"] == "nagios"