diff --git a/resources/scripts/Global.lua b/resources/scripts/Global.lua
index 1d85d15..c22cb70 100644
--- a/resources/scripts/Global.lua
+++ b/resources/scripts/Global.lua
@@ -314,3 +314,4 @@ registerCommand("wireframe", "commands/debug/ToggleWireframe.lua")
 registerCommand("invis", "commands/debug/ToggleInvisibility.lua")
 registerCommand("unlockaetheryte", "commands/debug/UnlockAetheryte.lua")
 registerCommand("teri", "commands/debug/ChangeTerritory.lua")
+registerCommand("ost", "commands/debug/OnScreenTest.lua")
diff --git a/resources/scripts/commands/debug/OnScreenTest.lua b/resources/scripts/commands/debug/OnScreenTest.lua
new file mode 100644
index 0000000..9836a10
--- /dev/null
+++ b/resources/scripts/commands/debug/OnScreenTest.lua
@@ -0,0 +1,10 @@
+required_rank = GM_RANK_DEBUG
+
+CHAT_LOG = 1
+ON_SCREEN = 4
+
+function onCommand(args, player)
+    player:send_message("this is a test of on-screen only", ON_SCREEN)
+    --player:send_message("this is an on-screen + chat log test", ON_SCREEN + CHAT_LOG)
+    player:send_message("this is a test of the chat log only, which omits a param")
+end
diff --git a/src/ipc/zone/mod.rs b/src/ipc/zone/mod.rs
index 29a1565..ec389cd 100644
--- a/src/ipc/zone/mod.rs
+++ b/src/ipc/zone/mod.rs
@@ -186,7 +186,20 @@ pub enum ServerZoneIpcData {
     Warp(Warp),
     /// Sent by the server when they send a chat message
     ServerChatMessage {
-        unk: u8, // channel?
+        /*
+         * bits (properties will apply when set, but a final base 10 value of zero defaults to chat log only):
+         * 76543210
+         * xxxxxSxC
+         * x = don't care/unused
+         * S = on-screen
+         * C = chat log
+         * all other bits are unused, therefore some possible examples are (base 10 values follow):
+         * 1 = chat log only
+         * 4 = on-screen only
+         * 5 = both
+         * ref: https://github.com/SapphireServer/Sapphire/blob/bf3368224a00c180cbb7ba413b52395eba58ec0b/src/common/Network/PacketDef/Zone/ServerZoneDef.h#L250
+         */
+        param: u8,
         #[brw(pad_after = 774)]
         #[br(count = 774)]
         #[br(map = read_string)]
@@ -447,7 +460,7 @@ mod tests {
             (
                 ServerZoneIpcType::ServerChatMessage,
                 ServerZoneIpcData::ServerChatMessage {
-                    unk: 0,
+                    param: 0,
                     message: String::new(),
                 },
             ),
diff --git a/src/world/connection.rs b/src/world/connection.rs
index a352d4f..2b982d7 100644
--- a/src/world/connection.rs
+++ b/src/world/connection.rs
@@ -610,7 +610,7 @@ impl ZoneConnection {
             timestamp: timestamp_secs(),
             data: ServerZoneIpcData::ServerChatMessage {
                 message: message.to_string(),
-                unk: 0,
+                param: 0,
             },
             ..Default::default()
         };
diff --git a/src/world/lua.rs b/src/world/lua.rs
index 910427e..dce8896 100644
--- a/src/world/lua.rs
+++ b/src/world/lua.rs
@@ -73,11 +73,11 @@ impl LuaPlayer {
         );
     }
 
-    fn send_message(&mut self, message: &str) {
+    fn send_message(&mut self, message: &str, param: u8) {
         let op_code = ServerZoneIpcType::ServerChatMessage;
         let data = ServerZoneIpcData::ServerChatMessage {
             message: message.to_string(),
-            unk: 0,
+            param,
         };
 
         self.create_segment_self(op_code, data);
@@ -225,8 +225,9 @@ impl LuaPlayer {
 
 impl UserData for LuaPlayer {
     fn add_methods<M: UserDataMethods<Self>>(methods: &mut M) {
-        methods.add_method_mut("send_message", |_, this, message: String| {
-            this.send_message(&message);
+        methods.add_method_mut("send_message", |lua, this, (message, param): (String, Value)| {
+            let param: u8 = lua.from_value(param).unwrap_or(0);
+            this.send_message(&message, param);
             Ok(())
         });
         methods.add_method_mut(