diff --git a/src/lib.cpp b/src/lib.cpp
index 53e0857..c4197d2 100644
--- a/src/lib.cpp
+++ b/src/lib.cpp
@@ -8,6 +8,7 @@
 #include <vector>
 
 enum VALIDATION_STATUS {
+    PLAYER_NOT_IN_ROOM,
     NO_PLAYER,
     ROOM_NOT_IN_PROGRESS,
     ACTION_PROHIBITED,
@@ -25,9 +26,9 @@ void run() {
     Event event2 = Event("Event 2", 1710087363, 1, true, {kill}, {});
     Event event3 = Event("Event 3", 1710087369, 1, true, {}, {kill});
     std::vector<Event> relatedEvents({event2, event3});
-    Player player1 = Player("player1", role1, PlayerStatus::ALIVE);
-    Player player2 = Player("player2", role1, PlayerStatus::ALIVE);
-    Room room1(1, "Room 1", 1710087364, RoomStatus::IN_PROGRESS, {player1, player2});
+    Player player1 = Player(69, "player1", role1, PlayerStatus::ALIVE);
+    Player player2 = Player(420, "player2", role1, PlayerStatus::ALIVE);
+    Room room1(1, "Room 1", 1710087364, RoomStatus::IN_PROGRESS, {});
     Room room2(2, "Room 2", 1710087384, RoomStatus::ENDED, {player1, player2});
     int actionValidated = validateAction(&player1, &kill, &room1, &relatedEvents, &player2);
     std::cout << actionValidated << std::endl;
@@ -35,6 +36,9 @@ void run() {
 
 int validateAction(
   Player *actor, const Action *action, Room *room, std::vector<Event> *relatedEvents, Player *target = nullptr) {
+    if (!playerBelongsToRoom(actor, room)) {
+        return PLAYER_NOT_IN_ROOM;
+    }
     if (!actor) {
         return NO_PLAYER;
     }
@@ -57,6 +61,10 @@ int validateAction(
     return ACTION_VALID;
 }
 
+bool playerBelongsToRoom(Player *player, Room *room) {
+    return std::find(room->players.begin(), room->players.end(), *player) != room->players.end();
+}
+
 bool actionBelongsToRole(Role *role, const Action *action) {
     return std::find(role->actions.begin(), role->actions.end(), *action) != role->actions.end();
 }
diff --git a/src/lib.hh b/src/lib.hh
index 425808d..bf9ec23 100644
--- a/src/lib.hh
+++ b/src/lib.hh
@@ -2,6 +2,7 @@
 
 void run();
 
+bool playerBelongsToRoom(Player *player, Room *room);
 bool actionBelongsToRole(Role *role, const Action *action);
 bool isActionAllowed(const Action *action, std::vector<Event> *relevantEvents);
 int validateAction(Player *actor, const Action *action, Room *room, std::vector<Event> *relatedEvents, Player *target);
diff --git a/src/prep/prep.cpp b/src/prep/prep.cpp
index 5ec4935..52253dc 100644
--- a/src/prep/prep.cpp
+++ b/src/prep/prep.cpp
@@ -2,6 +2,7 @@
 
 #include "timeUtils.hh"
 
+#include <cstdint>
 #include <initializer_list>
 
 int add(int a, int b) {
@@ -29,12 +30,17 @@ Role::Role(std::vector<Action> actions) {
     }
 }
 
-Player::Player(std::string username, Role role, PlayerStatus playerStatus):
+Player::Player(uint32_t id, std::string username, Role role, PlayerStatus playerStatus):
+    id(id),
     username(username),
     role(role),
     playerStatus(playerStatus) {
 }
 
+bool Player::operator==(const Player &other) const {
+    return this->id == other.id;
+}
+
 Room::Room(
   uint32_t id, std::string title, uint32_t utcTimestampCreatedAt, RoomStatus status, std::vector<Player> players):
     id(id),
diff --git a/src/prep/prep.hh b/src/prep/prep.hh
index 65a70ac..890ab17 100644
--- a/src/prep/prep.hh
+++ b/src/prep/prep.hh
@@ -53,11 +53,13 @@ struct Role {
 };
 
 struct Player {
+    uint32_t id;
     std::string username;
     Role role;
     PlayerStatus playerStatus;
 
-    Player(std::string username, Role role, PlayerStatus playerStatus);
+    Player(uint32_t id, std::string username, Role role, PlayerStatus playerStatus);
+    bool operator==(const Player &other) const;
 };
 
 struct Room {