diff --git a/cove-core/src/lib.rs b/cove-core/src/lib.rs
index 0e59125..4c7b3cc 100644
--- a/cove-core/src/lib.rs
+++ b/cove-core/src/lib.rs
@@ -1,25 +1,43 @@
+mod macros;
+
 use serde::{Deserialize, Serialize};
 
+use self::macros::packets;
+
+#[derive(Debug, Deserialize, Serialize)]
+pub struct Id(pub u128);
+
 #[derive(Debug, Deserialize, Serialize)]
 pub struct HelloCmd {
+    pub id: Id,
     pub name: String,
 }
 
 #[derive(Debug, Deserialize, Serialize)]
-pub struct HelloRpl {
-    pub msg: String,
+#[serde(tag = "type")]
+pub enum HelloRpl {
+    Success { id: Id },
+    InvalidName { reason: String },
+    NameAlreadyUsed,
+}
+
+// Create a Cmd enum for all commands and a Rpl enum for all replies, as well as
+// TryFrom impls for the individual command and reply structs.
+packets! {
+    Hello(HelloCmd, HelloRpl),
 }
 
 #[derive(Debug, Deserialize, Serialize)]
 #[serde(tag = "type")]
-pub enum Data {
-    HelloCmd(HelloCmd),
-    HelloRpl(HelloRpl),
-}
-
-#[derive(Debug, Deserialize, Serialize)]
-pub struct Packet {
-    pub id: u64,
-    #[serde(flatten)]
-    pub data: Data,
+pub enum Packet {
+    Cmd {
+        id: u64,
+        #[serde(flatten)]
+        cmd: Cmd,
+    },
+    Rpl {
+        id: u64,
+        #[serde(flatten)]
+        rpl: Rpl,
+    },
 }
diff --git a/cove-core/src/macros.rs b/cove-core/src/macros.rs
new file mode 100644
index 0000000..aa9b737
--- /dev/null
+++ b/cove-core/src/macros.rs
@@ -0,0 +1,43 @@
+macro_rules! packets {
+    ( $( $name:ident($cmd:ident, $rpl:ident), )* ) => {
+        #[derive(Debug, Deserialize, Serialize)]
+        #[serde(tag = "name", content = "data")]
+        pub enum Cmd {
+            $( $name($cmd), )*
+        }
+
+        $(
+            impl std::convert::TryFrom<Cmd> for $cmd {
+                type Error = ();
+                fn try_from(cmd: Cmd) -> Result<Self, Self::Error> {
+                    match cmd {
+                        Cmd::$name(val) => Ok(val),
+                        _ => Err(()),
+                    }
+                }
+            }
+        )*
+
+        #[derive(Debug, Deserialize, Serialize)]
+        #[serde(tag = "name", content = "data")]
+        pub enum Rpl {
+            $( $name($rpl), )*
+        }
+
+        $(
+            impl std::convert::TryFrom<Rpl> for $rpl {
+                type Error = ();
+                fn try_from(rpl: Rpl) -> Result<Self, Self::Error> {
+                    match rpl {
+                        Rpl::$name(val) => Ok(val),
+                        _ => Err(()),
+                    }
+                }
+            }
+        )*
+    };
+}
+
+// Make macro importable from elsewhere
+// See https://stackoverflow.com/a/31749071
+pub(crate) use packets;
diff --git a/cove-server/src/main.rs b/cove-server/src/main.rs
index f10fa8f..db2845f 100644
--- a/cove-server/src/main.rs
+++ b/cove-server/src/main.rs
@@ -1,12 +1,11 @@
-use cove_core::{Data, HelloCmd, Packet};
+use cove_core::{HelloCmd, HelloRpl, Id, Packet, Rpl};
 
 fn main() {
-    println!("Hello, world!");
-    let packet = Packet {
+    let packet = Packet::Rpl {
         id: 1337,
-        data: Data::HelloCmd(HelloCmd {
-            name: "Garmy".to_string(),
+        rpl: Rpl::Hello(HelloRpl::InvalidName {
+            reason: "abc".to_string(),
         }),
     };
-    println!("{}", serde_json::to_string(&packet).unwrap());
+    println!("{}", serde_json::to_string_pretty(&packet).unwrap());
 }