diff --git a/blog/2023-02-27-checkin/readme.md b/blog/2023-02-27-checkin/readme.md
new file mode 100644
index 0000000..9728870
--- /dev/null
+++ b/blog/2023-02-27-checkin/readme.md
@@ -0,0 +1,49 @@
+# Checkin
+
+where do these names come from?
+
+~~~go
+req_body := protobuf.Message{
+   4: protobuf.Message{ // checkin
+      1: protobuf.Message{ // build
+         // sdkVersion
+         // multiple APK valid range 14 - 0x7FFF_FFFF
+         // single APK valid range 14 - 28
+         10: protobuf.Varint(28),
+      },
+      18: protobuf.Varint(1), // voiceCapable
+   },
+   // version
+   // valid range 2 - 3
+   14: protobuf.Varint(3),
+   18: protobuf.Message{ // deviceConfiguration
+      1: protobuf.Varint(c.Touch_Screen),
+      2: protobuf.Varint(c.Keyboard),
+      3: protobuf.Varint(c.Navigation),
+      4: protobuf.Varint(c.Screen_Layout),
+      5: protobuf.Varint(c.Has_Hard_Keyboard),
+      6: protobuf.Varint(c.Has_Five_Way_Navigation),
+      7: protobuf.Varint(c.Screen_Density),
+      8: protobuf.Varint(c.GL_ES_Version),
+      11: protobuf.String(native_platform),
+   },
+}
+for _, library := range c.System_Shared_Library {
+   // .deviceConfiguration.systemSharedLibrary
+   req_body.Get(18).Add_String(9, library)
+}
+for _, extension := range c.GL_Extension {
+   // .deviceConfiguration.glExtension
+   req_body.Get(18).Add_String(15, extension)
+}
+for _, name := range c.New_System_Available_Feature {
+   // .deviceConfiguration.newSystemAvailableFeature
+   req_body.Get(18).Add(26, protobuf.Message{
+      1: protobuf.String(name),
+   })
+}
+req, err := http.NewRequest(
+   "POST", "https://android.googleapis.com/checkin",
+   bytes.NewReader(req_body.Marshal()),
+)
+~~~
diff --git a/blog/go.mod b/blog/go.mod
deleted file mode 100644
index 9c323af..0000000
--- a/blog/go.mod
+++ /dev/null
@@ -1,3 +0,0 @@
-module blog
-
-go 1.20