diff --git a/Server/Server.hpp b/Server/Server.hpp
index 6fd8ed1..1f332ea 100644
--- a/Server/Server.hpp
+++ b/Server/Server.hpp
@@ -6,7 +6,7 @@
 /*   By: aortigos <aortigos@student.42malaga.com    +#+  +:+       +#+        */
 /*                                                +#+#+#+#+#+   +#+           */
 /*   Created: 2026/05/06 17:18:11 by iherman-          #+#    #+#             */
-/*   Updated: 2026/05/14 20:35:22 by aortigos         ###   ########.fr       */
+/*   Updated: 2026/05/15 11:40:28 by aortigos         ###   ########.fr       */
 /*                                                                            */
 /* ************************************************************************** */
 
@@ -22,10 +22,12 @@
 # include <vector>
 # include <map>
 
+# include <cctype>
+
 # include "../User/User.hpp"
 
 
-# define SERVER_NAME irc.server
+# define SERVER_NAME "irc.server"
 # define PORT_DEFAULT 9898
 
 class Server
diff --git a/cmds/nick.cpp b/cmds/nick.cpp
index f80a896..13649de 100644
--- a/cmds/nick.cpp
+++ b/cmds/nick.cpp
@@ -6,7 +6,7 @@
 /*   By: aortigos <aortigos@student.42malaga.com    +#+  +:+       +#+        */
 /*                                                +#+#+#+#+#+   +#+           */
 /*   Created: 2026/05/10 22:06:22 by aortigos          #+#    #+#             */
-/*   Updated: 2026/05/14 20:38:44 by aortigos         ###   ########.fr       */
+/*   Updated: 2026/05/15 11:46:03 by aortigos         ###   ########.fr       */
 /*                                                                            */
 /* ************************************************************************** */
 
@@ -19,10 +19,45 @@ void	Server::nick_cmd(User &client, std::istringstream &ss)
 	ss >> args;
 	if (args.empty())
 		return (client.send(":" SERVER_NAME " 431 * :Not nickname given\r\n"));
-	// Invalid characters in nick
-		// 432 * badnick : Erroneous nickname
-	// If nick exists
-		// 4233 * takenick :Nickname is already in use
-	if (client.getUsername())
-		return (); // Broadcast in channels :oldnick!user@host NICK newnick
+	if (!isValidNick(args))
+		return (client.send(":" SERVER_NAME " 432 * " + args + ":Erroneous nickname\r\n"))
+	for (std::map<int, User>::iterator it = clients_.begin(); it != clients_.end(); it++)
+	{
+		if (it->second.getNick() == args)
+			return (client.send(":" SERVER_NAME " 433 * " + args + " :Nickname is already in use\r\n"))
+	}
+	
+	std::string oldNick = client.getNick();
+	client.setNick(args);
+
+	if (client.isRegistered())
+	{
+		// Change nick to an already registered user
+		// Send message to his channels
+		//client.broadcast(":" + oldNick + "!~" + client.getUsername() + "@hostt NICK " + args + "\r\n");
+		return ;
+	}
+
+	if (!client.getUsername().empty())
+	{
+		client.setRegistered(true);
+		client.send(":" SERVER_NAME " 001 " + args + " :Welcome to the IRC Network " + args + "\r\n");
+		client.send(":" SERVER_NAME " 002 " + args + " :Your host is " SERVER_NAME ", running version 1.0\r\n");
+		client.send(":" SERVER_NAME " 003 " + args + " :This server was created May 2026\r\n");
+		client.send(":" SERVER_NAME " 004 " + args + " :" SERVER_NAME " 1.0\r\n");
+	}
+}
+
+static bool isValidNick(const std::string &nick)
+{
+	const std::string special = "[]\\`_^{|}";
+
+	if (!isalpha(nick[0]) && special.find(nick[0]) == std::string::npos)
+		return (false);
+	for (size_t i = 1; i < nick.size(); i++)
+	{
+		if (!isalnum(nick[i])) && special.find(nick[i] == std::string::npos && nick[i] != '-')
+			return (false);
+	}
+	return (true);
 }
\ No newline at end of file