diff --git a/include/packet.h b/include/packet.h
new file mode 100644
index 0000000..d045efe
--- /dev/null
+++ b/include/packet.h
@@ -0,0 +1,13 @@
+#pragma once
+#include <stdint.h>
+
+typedef struct {
+    uint8_t version;           // version number to prevent breaking older packet formats
+    uint8_t ttl;               // the number of hops left in the lifespan of the packet, prevents infinite hopping
+    uint8_t packetType;        // packet type (message is the only type right now)
+    uint32_t senderId;         // unique id of the person who sent the packet
+    uint32_t targetId;         // 0xFFFFFFFF = broadcast
+    uint32_t messageId;        // we can ignore packets if we've seen them twice
+    uint16_t payloadLength;    // length of data
+    uint8_t payload[];         // actual data
+} __attribute__((packed)) Packet;
\ No newline at end of file
diff --git a/relay/main.c b/relay/main.c
index 1aed12a..bdfc784 100644
--- a/relay/main.c
+++ b/relay/main.c
@@ -1,3 +1,5 @@
+#include "../include/packet.h"
+
 #include "pico/stdlib.h"
 
 #define LED_PIN 25