diff --git a/crates/game-service/src/battle_session.rs b/crates/game-service/src/battle_session.rs
index e961ea3..e1fe9a9 100644
--- a/crates/game-service/src/battle_session.rs
+++ b/crates/game-service/src/battle_session.rs
@@ -209,6 +209,9 @@ impl BattleSession {
     pub fn stars(&self) -> (i32, i32) {
         (self.mode.battle.stars(0), self.mode.battle.stars(1))
     }
+    pub fn checksum(&self) -> Option<i32> {
+        self.mode.calculate_checksum().ok()
+    }
     pub fn towers_standing(&self) -> (usize, usize) {
         (
             self.mode.battle.leader_towers[0].len(),
@@ -319,6 +322,7 @@ impl BattleRegistry {
             stars: session.stars(),
             objects: session.object_count(),
             towers: session.towers_standing(),
+            checksum: session.checksum(),
         })
     }
     pub async fn play<F>(
@@ -356,4 +360,5 @@ pub struct BattleProgress {
     pub stars: (i32, i32),
     pub objects: usize,
     pub towers: (usize, usize),
+    pub checksum: Option<i32>,
 }
diff --git a/crates/game-service/src/service.rs b/crates/game-service/src/service.rs
index 7ab5dcc..4940400 100644
--- a/crates/game-service/src/service.rs
+++ b/crates/game-service/src/service.rs
@@ -366,9 +366,14 @@ impl GameApi for GameService {
                     .await;
             }
             let progress = self.running_battles.advance(account, turn.tick).await;
+            let server_checksum = progress.and_then(|state| state.checksum);
+            let agrees = server_checksum == Some(turn.checksum);
             tracing::info!(
                 %account,
                 tick = turn.tick,
+                checksum = turn.checksum,
+                server_checksum,
+                agrees,
                 seconds = progress.map(|state| state.seconds),
                 finished = progress.map(|state| state.finished),
                 stars = ?progress.map(|state| state.stars),
diff --git a/crates/logic/src/battle/logic_game_mode.rs b/crates/logic/src/battle/logic_game_mode.rs
index aa1f5e2..facac68 100644
--- a/crates/logic/src/battle/logic_game_mode.rs
+++ b/crates/logic/src/battle/logic_game_mode.rs
@@ -23,10 +23,10 @@ impl LogicGameMode {
         Ok(writer.into_inner())
     }
 }
-impl Payload for LogicGameMode {
-    fn encode(&self, writer: &mut ByteStreamWriter) -> Result<()> {
+impl LogicGameMode {
+    pub fn write(&self, writer: &mut ByteStreamWriter, with_commands: bool) -> Result<()> {
         writer.write_vint(self.server_tick);
-        writer.write_vint(0);
+        writer.write_checksum_checkpoint();
         writer.write_vint(SECTION_BATTLE);
         self.time.encode(writer)?;
         self.random.encode(writer)?;
@@ -37,10 +37,22 @@ impl Payload for LogicGameMode {
         }
         writer.write_vint(SECTION_TUTORIAL);
         self.tutorial_manager.encode(writer)?;
-        writer.write_vint(0);
-        writer.write_vint(0);
+        writer.write_checksum_checkpoint();
+        if with_commands {
+            writer.write_vint(0);
+        }
         Ok(())
     }
+    pub fn calculate_checksum(&self) -> Result<i32> {
+        let mut writer = ByteStreamWriter::new();
+        self.write(&mut writer, false)?;
+        Ok(writer.checksum() as i32)
+    }
+}
+impl Payload for LogicGameMode {
+    fn encode(&self, writer: &mut ByteStreamWriter) -> Result<()> {
+        self.write(writer, true)
+    }
     fn decode(_reader: &mut titan::ByteStreamReader<'_>) -> Result<Self> {
         Err(titan::Error::Unsupported("LogicGameMode is encode only"))
     }
diff --git a/crates/titan/src/io/writer.rs b/crates/titan/src/io/writer.rs
index c89234c..71c3939 100644
--- a/crates/titan/src/io/writer.rs
+++ b/crates/titan/src/io/writer.rs
@@ -33,6 +33,10 @@ impl ByteStreamWriter {
     pub fn checksum(&self) -> u32 {
         self.checksum.value()
     }
+    pub fn write_checksum_checkpoint(&mut self) {
+        let running = self.checksum.value() as i32;
+        self.write_vint(running);
+    }
     pub fn write_byte(&mut self, value: u8) {
         self.checksum.write_byte(value as i8);
         self.bit_index = 0;