diff --git a/dotnet/SafelyYou/Api/ErrorResponse.cs b/dotnet/SafelyYou/Api/ErrorResponse.cs
new file mode 100644
index 0000000..4d8041a
--- /dev/null
+++ b/dotnet/SafelyYou/Api/ErrorResponse.cs
@@ -0,0 +1,7 @@
+using System.Text.Json.Serialization;
+
+namespace SafelyYou.Api;
+
+public record ErrorResponse(
+    [property: JsonPropertyName("msg")] string Msg
+);
diff --git a/dotnet/SafelyYou/Api/GetDeviceStatsResponse.cs b/dotnet/SafelyYou/Api/GetDeviceStatsResponse.cs
new file mode 100644
index 0000000..696a895
--- /dev/null
+++ b/dotnet/SafelyYou/Api/GetDeviceStatsResponse.cs
@@ -0,0 +1,8 @@
+using System.Text.Json.Serialization;
+
+namespace SafelyYou.Api;
+
+public record GetDeviceStatsResponse(
+    [property: JsonPropertyName("avg_upload_time")] string AvgUploadTime,
+    [property: JsonPropertyName("uptime")] double Uptime
+);
diff --git a/dotnet/SafelyYou/Api/HeartbeatRequest.cs b/dotnet/SafelyYou/Api/HeartbeatRequest.cs
new file mode 100644
index 0000000..1b0a43f
--- /dev/null
+++ b/dotnet/SafelyYou/Api/HeartbeatRequest.cs
@@ -0,0 +1,7 @@
+using System.Text.Json.Serialization;
+
+namespace SafelyYou.Api;
+
+public record HeartbeatRequest(
+    [property: JsonPropertyName("sent_at")] DateTimeOffset SentAt
+);
diff --git a/dotnet/SafelyYou/Api/NotFoundResponse.cs b/dotnet/SafelyYou/Api/NotFoundResponse.cs
new file mode 100644
index 0000000..3e82848
--- /dev/null
+++ b/dotnet/SafelyYou/Api/NotFoundResponse.cs
@@ -0,0 +1,7 @@
+using System.Text.Json.Serialization;
+
+namespace SafelyYou.Api;
+
+public record NotFoundResponse(
+    [property: JsonPropertyName("msg")] string Msg
+);
diff --git a/dotnet/SafelyYou/Api/UploadStatsRequest.cs b/dotnet/SafelyYou/Api/UploadStatsRequest.cs
new file mode 100644
index 0000000..bd2e1c2
--- /dev/null
+++ b/dotnet/SafelyYou/Api/UploadStatsRequest.cs
@@ -0,0 +1,8 @@
+using System.Text.Json.Serialization;
+
+namespace SafelyYou.Api;
+
+public record UploadStatsRequest(
+    [property: JsonPropertyName("sent_at")] DateTimeOffset SentAt,
+    [property: JsonPropertyName("upload_time")] long UploadTime
+);