diff --git a/api/chat.js b/api/chat.js
index 03be510..ce9015a 100644
--- a/api/chat.js
+++ b/api/chat.js
@@ -1,22 +1,46 @@
 const path = require("path");
 const { addMessage } = require(path.join(__dirname + "/redis.js"));
 
+const validateUsername = (username) => {
+  let error = undefined;
+  const illegalChars = /\W/;
+  const minLength = 3;
+  const maxLength = 15;
+
+  if (typeof username !== 'string') {
+    error = 'Ugyldig brukernavn.';
+  } else if (username.length === 0) {
+    error = 'Vennligst oppgi brukernavn.';
+  } else if (username.length < minLength || username.length > maxLength) {
+    error = `Brukernavn må være mellom ${minLength}-${maxLength} karaktere.`
+  } else if (illegalChars.test(username)) {
+    error = 'Brukernavn kan bare inneholde tall og bokstaver.'
+  }
+
+  return error;
+}
+
 const io = (io) => {
   io.on("connection", socket => {
     let username = null;
 
     socket.on("username", msg => {
-      if (msg.username == null) {
+      const usernameValidationError = validateUsername(msg.username);
+      if (usernameValidationError) {
         username = null;
-        socket.emit("accept_username", false);
-        return;
-      }
-      if (msg.username.length > 3 && msg.username.length < 30) {
+        socket.emit("accept_username", {
+          reason: usernameValidationError,
+          success: false,
+          username: undefined
+        });
+      } else {
         username = msg.username;
-        socket.emit("accept_username", true);
-        return;
+        socket.emit("accept_username", {
+          reason: undefined,
+          success: true,
+          username: msg.username
+        });
       }
-      socket.emit("accept_username", false);
     });
 
     socket.on("chat", msg => {