diff --git a/HanvonHttpDiagnostics.cs b/HanvonHttpDiagnostics.cs
new file mode 100644
index 0000000..6bbe465
--- /dev/null
+++ b/HanvonHttpDiagnostics.cs
@@ -0,0 +1,93 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+using System.Text.RegularExpressions;
+
+namespace HanvonF710XAttendanceService
+{
+    internal sealed class HttpExchangeResult
+    {
+        public string Url { get; set; }
+        public string Method { get; set; } = "POST";
+        public string RequestContentType { get; set; }
+        public string RequestBodySanitized { get; set; }
+        public int StatusCode { get; set; }
+        public string ResponseHeaders { get; set; }
+        public string ResponseBody { get; set; }
+        public Dictionary<string, object> ParsedResponse { get; set; }
+        public string Error { get; set; }
+
+        public bool IsHttpSuccess => StatusCode >= 200 && StatusCode < 300;
+    }
+
+    internal static class HanvonHttpDiagnostics
+    {
+        public static string SanitizeJsonBody(string json)
+        {
+            if (string.IsNullOrEmpty(json)) return json;
+            string sanitized = Regex.Replace(json, "(\"password\"\\s*:\\s*\")([^\"]*)(\")", "$1***$3", RegexOptions.IgnoreCase);
+            sanitized = Regex.Replace(sanitized, "(\"record\"\\s*:\\s*\")([^\"]{80})[^\"]*(\")", "$1$2...[truncated]$3", RegexOptions.IgnoreCase);
+            sanitized = Regex.Replace(sanitized, "(\"face\"\\s*:\\s*\")([^\"]{80})[^\"]*(\")", "$1$2...[truncated]$3", RegexOptions.IgnoreCase);
+            return sanitized;
+        }
+
+        public static string DescribeTemplatePayload(string payload, string pushMode)
+        {
+            if (string.IsNullOrWhiteSpace(payload)) return "empty";
+            string mode = pushMode ?? "unknown";
+            int len = payload.Length;
+            string prefix = payload.Length > 24 ? payload.Substring(0, 24) : payload;
+            try
+            {
+                byte[] decoded = Convert.FromBase64String(payload.Length > 256 ? payload.Substring(0, 256) : payload);
+                if (decoded.Length >= 3)
+                {
+                    return $"mode={mode} base64_len={len} decoded_prefix=0x{decoded[0]:X2}{decoded[1]:X2}{decoded[2]:X2} jpeg={(decoded[0] == 0xFF && decoded[1] == 0xD8)}";
+                }
+            }
+            catch
+            {
+                return $"mode={mode} base64_len={len} prefix={prefix} (not standard base64 JPEG header)";
+            }
+            return $"mode={mode} base64_len={len} prefix={prefix}";
+        }
+
+        public static void WriteExchange(TextWriter writer, string phase, string empId, HttpExchangeResult exchange)
+        {
+            writer.WriteLine($"[DB_TO_DEVICE] emp={empId} {phase}");
+            writer.WriteLine($"URL={exchange?.Url ?? "(null)"}");
+            writer.WriteLine($"HTTP={exchange?.StatusCode ?? 0}");
+            writer.WriteLine($"Method={exchange?.Method ?? "POST"}");
+            writer.WriteLine($"Content-Type={exchange?.RequestContentType ?? "(null)"}");
+            writer.WriteLine($"request={exchange?.RequestBodySanitized ?? "(null)"}");
+            if (!string.IsNullOrWhiteSpace(exchange?.ResponseHeaders))
+            {
+                writer.WriteLine($"response_headers={exchange.ResponseHeaders}");
+            }
+            writer.WriteLine($"response={exchange?.ResponseBody ?? exchange?.Error ?? "(null)"}");
+        }
+
+        public static void WriteResultSummary(
+            TextWriter writer,
+            string empId,
+            bool userExistsInList,
+            string listId,
+            string listName,
+            string listFaceField,
+            bool profileOk,
+            string profileFaceFlag,
+            string profilePhotoUrl,
+            bool recordOk,
+            int recordLen,
+            string templateFormat)
+        {
+            writer.WriteLine($"[DB_TO_DEVICE] emp={empId} RESULT");
+            writer.WriteLine($"user_exists={(userExistsInList ? "true" : "false")} list_id={listId ?? ""} list_name={listName ?? ""} list_face={listFaceField ?? ""}");
+            writer.WriteLine($"profile_getuserinfo_ok={profileOk} faceflag={profileFaceFlag ?? ""} photourl={profilePhotoUrl ?? ""}");
+            writer.WriteLine($"face_exists={(recordOk ? "true" : "false")} backupnum_record_len={recordLen}");
+            writer.WriteLine($"template_format={templateFormat ?? ""}");
+        }
+    }
+}