diff --git a/.gitignore b/.gitignore
index 8222304..1d00464 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,10 @@ server/build/
 server/*.o
 server/*.out
 
+*.json
+
+server/.cache/
+
 # Node dependencies.
 client/node_modules/
 
diff --git a/server/src/api.c b/server/src/api.c
new file mode 100644
index 0000000..b233f8f
--- /dev/null
+++ b/server/src/api.c
@@ -0,0 +1,28 @@
+#include "include/data.h"
+
+PacketType packet_type_parse(const char* type_str) {
+    if (!type_str) return PACKET_TYPE_INVALID;
+    if (!strcmp(type_str, "join")) return PACKET_TYPE_JOIN;
+    if (!strcmp(type_str, "JOIN_EV")) return PACKET_TYPE_JOIN_EV;
+    return PACKET_TYPE_INVALID;
+}
+
+Packet* packet_init(PacketType type, void* data) {
+    Packet* packet = malloc(sizeof(Packet));
+    if (!packet) return NULL;
+
+    packet->type = type;
+    packet->data = data;
+
+    return packet;
+}
+
+Packet* packet_init_untrusted(PacketType type, void* data) {
+    Packet* packet = malloc(sizeof(Packet));
+    if (!packet) return NULL;
+
+    packet->type = type;
+    packet->data = data;
+
+    return packet;
+}
diff --git a/server/src/data.c b/server/src/data.c
new file mode 100644
index 0000000..cb5f459
--- /dev/null
+++ b/server/src/data.c
@@ -0,0 +1,13 @@
+#include "include/data.h"
+
+int name_verify(const char* name) {
+    if (!name) return 0;
+    if (strlen(name) > NAME_MAX_LENGTH) return 0;
+    return 1;
+}
+
+int msg_verify(const char* content) {
+    if (!content) return 0;
+    if (strlen(content) > MSG_MAX_LENGTH) return 0;
+    return 1;
+}
diff --git a/server/src/include/api.h b/server/src/include/api.h
new file mode 100644
index 0000000..1f4a48f
--- /dev/null
+++ b/server/src/include/api.h
@@ -0,0 +1,41 @@
+#ifndef API__H
+#define API__H
+
+#include "data.h"
+
+typedef enum {
+    PACKET_TYPE_JOIN,
+    PACKET_TYPE_WELCOME,
+    PACKET_TYPE_JOIN_EV,
+} PacketType;
+
+static const char* packet_type_strings[] = {
+   [PACKET_TYPE_JOIN]= "join",
+   [PACKET_TYPE_WELCOME]= "welcome",
+   [PACKET_TYPE_JOIN_EV]= "join_ev",
+};
+
+PacketType packet_type_parse(const char* type_str);
+
+typedef struct {
+    PacketType type;
+    void* data;
+} Packet;
+
+Packet* packet_init(PacketType type, void* data);
+Packet* packet_init_untrusted(PacketType type, void* data);
+
+typedef struct {
+    Name name;
+} PacketJoin;
+
+typedef struct {
+    UserData* online;
+    MsgData* history;
+} PacketWelcome;
+
+typedef struct {
+    UserData newguy;
+} PacketJoinEvent;
+
+#endif
diff --git a/server/src/include/data.h b/server/src/include/data.h
new file mode 100644
index 0000000..da37e91
--- /dev/null
+++ b/server/src/include/data.h
@@ -0,0 +1,31 @@
+#ifndef DATA__H
+#define DATA__H
+
+#include <time.h>
+
+#define NAME_MAX_LENGTH 16
+#define MSG_MAX_LENGTH 1024
+
+typedef int UserID;
+typedef int MsgID;
+
+typedef char Name[NAME_MAX_LENGTH];
+int name_verify(const char* name);
+
+typedef char MsgContent[MSG_MAX_LENGTH];
+int msg_verify(const char* content);
+
+typedef struct {
+    UserID id;
+    Name name;
+} UserData;
+
+typedef struct {
+    MsgID id;
+    UserData author;
+    MsgID parent;
+    MsgContent content;
+    time_t timestamp;
+} MsgData;
+
+#endif