diff --git a/src/auth/auth.cpp b/src/auth/auth.cpp
index 36259fa..0ea9703 100644
--- a/src/auth/auth.cpp
+++ b/src/auth/auth.cpp
@@ -1,15 +1,26 @@
 #include "auth.hpp"
 #include "../colors.h"
+#include "../includes.hpp"
+#include <jwt-cpp/jwt.h>
 
 // function for authorization users
-void auth(const httplib::Request& request, httplib::Response& response) {
+void auth(const httplib::Request &request, httplib::Response &response) {
     std::cout << GREEN << request.path << RESET << "  " << request.method << std::endl;
     response.set_header("Access-Control-Allow-Origin", "*");
-    if (request.body == "") {response.set_content("{\"required\":\"[username,password]\"}", "application/json");return;}
+    if (request.body.empty()) {
+        response.set_content(AUTH_REQUIRED_STRING, JSON_TYPE);
+        return;
+    }
     nlohmann::json json_body = nlohmann::json::parse(request.body);
 
-    if (json_body["username"] == nullptr) {response.set_content("{\"required\":\"[username,password]\"}", "application/json");return;}
-    if (json_body["password"] == nullptr) {response.set_content("{\"required\":\"[username,password]\"}", "application/json");return;}
+    if (json_body["username"] == nullptr) {
+        response.set_content(AUTH_REQUIRED_STRING, JSON_TYPE);
+        return;
+    }
+    if (json_body["password"] == nullptr) {
+        response.set_content(AUTH_REQUIRED_STRING, JSON_TYPE);
+        return;
+    }
     const std::string request_username = json_body["username"];
     const std::string request_password = json_body["password"];
 
@@ -17,23 +28,25 @@ void auth(const httplib::Request& request, httplib::Response& response) {
     nlohmann::json all_users = nlohmann::json::parse(usersfile);
     usersfile.close();
 
-    std::string userid = "";
-    for (int i = 0; i < all_users.size(); i++) {
-        if ((all_users[i]["username"] == request_username) && (all_users[i]["password"] == request_password)) {
-            userid = all_users[i]["id"];
+    std::string userid;
+    for (nlohmann::basic_json<> user: all_users) {
+        if ((user["username"] == request_username) && (user["password"] == request_password)) {
+            userid = user["id"];
             break;
         }
     }
-
-    if (userid == "") {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    if (userid.empty()) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
 
     std::string token = jwt::create()
-        .set_type("JWT")
-        .set_issuer("auth0")
-        .set_payload_claim("userId", jwt::claim(userid))
-        .sign(jwt::algorithm::hs256{JWT_SECRET_KEY});
+            .set_type("JWT")
+            .set_issuer("auth0")
+            .set_payload_claim("userId", jwt::claim(userid))
+            .sign(jwt::algorithm::hs256{JWT_SECRET_KEY});
 
     std::stringstream response_json;
-    response_json << "{\"token\":\"" << token << "\"}";
-    response.set_content(response_json.str(), "application/json");
+    response_json << R"({"token":")" << token << "\"}";
+    response.set_content(response_json.str(), JSON_TYPE);
 }
diff --git a/src/auth/auth.hpp b/src/auth/auth.hpp
index a8a3429..f517929 100644
--- a/src/auth/auth.hpp
+++ b/src/auth/auth.hpp
@@ -2,16 +2,12 @@
 #define AUTH_HPP
 
 #include <httplib.h>
-#include <jwt-cpp/jwt.h>
 #include <json.hpp>
-#include <string>
-#include <fstream>
-#include "../includes.hpp"
-#include <sstream>
 
 // function for authorization users
-void auth(const httplib::Request& request, httplib::Response& response);
+void auth(const httplib::Request &request, httplib::Response &response);
+
 // function for verify tokens
-bool verify_auth(const std::string token);
+bool verify_auth(const std::string &token);
 
 #endif // AUTH_HPP
diff --git a/src/auth/verify_auth.cpp b/src/auth/verify_auth.cpp
index 1dc9d8d..e01b6b3 100644
--- a/src/auth/verify_auth.cpp
+++ b/src/auth/verify_auth.cpp
@@ -1,24 +1,25 @@
 #include "auth.hpp"
+#include <jwt-cpp/jwt.h>
+#include "../includes.hpp"
 
 // function for verify tokens
-bool verify_auth(const std::string token) {
+bool verify_auth(const std::string &token) {
     try {
         // parse token
         const jwt::decoded_jwt<jwt::traits::kazuho_picojson> decoded = jwt::decode(token);
 
         // validate token
         const jwt::verifier<jwt::default_clock, jwt::traits::kazuho_picojson> verifier = jwt::verify()
-                                .allow_algorithm(jwt::algorithm::hs256{JWT_SECRET_KEY})
-                                .with_issuer("auth0");
+                .allow_algorithm(jwt::algorithm::hs256{JWT_SECRET_KEY})
+                .with_issuer("auth0");
 
         verifier.verify(decoded);
         return true;
-    }
-    catch (const std::system_error& e) {
+    } catch (const std::system_error &e) {
         std::cout << "Verification error: " << e.what() << std::endl;
         return false;
     }
     catch (...) {
         return false;
     }
-}
\ No newline at end of file
+}
diff --git a/src/auth_service.cpp b/src/auth_service.cpp
index be82972..effb9f8 100644
--- a/src/auth_service.cpp
+++ b/src/auth_service.cpp
@@ -1,9 +1,6 @@
 #include <iostream>
-#include <fstream>
 #include <httplib.h>
 #include <json.hpp>
-#include <jwt-cpp/jwt.h>
-
 #include "auth/auth.hpp"
 #include "users/users.hpp"
 #include "colors.h"
@@ -29,9 +26,9 @@ int main() {
     srv.set_mount_point("/admin", "../src/web");
     srv.set_mount_point("/js", "../src/web/js");
     srv.set_mount_point("/css", "../src/web/css");
-    
-    std::cout << GREEN << "Starting" << RESET << " server on [ " << YELLOW \
-        << "localhost" << RESET << ":" << CYAN << "43243" << RESET << " ]" << std::endl;
+
+    std::cout << GREEN << "Starting" << RESET << " server on [ " << YELLOW
+            << "localhost" << RESET << ":" << CYAN << "43243" << RESET << " ]" << std::endl;
     srv.listen("localhost", 43243);
     return 0;
 }
diff --git a/src/colors.h b/src/colors.h
index fa6270b..98570c0 100644
--- a/src/colors.h
+++ b/src/colors.h
@@ -74,4 +74,4 @@
 #define ON_ICYAN "\033[0;106m"    // CYAN
 #define ON_IWHITE "\033[0;107m"   // WHITE
 
-#endif // C_COLORS_H
\ No newline at end of file
+#endif // C_COLORS_H
diff --git a/src/includes.hpp b/src/includes.hpp
index 1d48df6..e7e79f5 100644
--- a/src/includes.hpp
+++ b/src/includes.hpp
@@ -2,5 +2,13 @@
 #define INCLUDES_HPP
 
 #define JWT_SECRET_KEY "secret"
+#define STRING403 R"({"status":"403"})"
+#define JSON_TYPE "application/json"
+#define AUTH_REQUIRED_STRING R"({"required":"[username,password]"})"
+#define ACCESS_REQUIRED_STRING R"({"required":"[token]"})"
+#define ADD_USER_REQUIRED_STRING R"({"required":"[token,username,password]","optional":"[group,is_superuser]"})"
+#define CHANGE_PASSWORD_REQUIRED_STRING R"({"required":"[token,old_password,new_password] or if you superuser [token,userid,new_password]"})"
+#define CHANGE_USER_REQUIRED_STRING R"({"required":"[token] or if you superuser [token,userid]","optional":"[username,password,is_superuser,group]"})"
+#define DELETE_USER_REQUIRED_STRING R"({"required":"[token] or if you superuser [token,userid]"})"
 
-#endif // INCLUDES_HPP
\ No newline at end of file
+#endif // INCLUDES_HPP
diff --git a/src/security/cors.cpp b/src/security/cors.cpp
index 773b5e3..41a6cf1 100644
--- a/src/security/cors.cpp
+++ b/src/security/cors.cpp
@@ -1,10 +1,9 @@
 #include "cors.hpp"
 #include "../colors.h"
 
-void set_cors_headers(const httplib::Request& request, httplib::Response& response) {
+void set_cors_headers(const httplib::Request &request, httplib::Response &response) {
     std::cout << GREEN << request.path << "  " << std::endl;
     response.set_header("Access-Control-Allow-Origin", "*");
     response.set_header("Access-Control-Allow-Methods", "GET,POST,OPTIONS");
     response.set_header("Access-Control-Allow-Headers", "Authorization,X-Custom,Content-Type");
 }
-
diff --git a/src/security/cors.hpp b/src/security/cors.hpp
index 842bbe1..a132184 100644
--- a/src/security/cors.hpp
+++ b/src/security/cors.hpp
@@ -5,9 +5,9 @@
 
 #ifdef CORS_ENABLE
 
+// function to set cors headers
 void set_cors_headers(const httplib::Request& request, httplib::Response& response);
 
 #endif // CORS_ENABLE
 
 #endif // CORS_HPP
-
diff --git a/src/users/access_request.cpp b/src/users/access_request.cpp
index 85f0ad1..d0adf5c 100644
--- a/src/users/access_request.cpp
+++ b/src/users/access_request.cpp
@@ -1,14 +1,25 @@
 #include "users.hpp"
 #include "../colors.h"
+#include "../includes.hpp"
+#include "../auth/auth.hpp"
 
 // function for access or reject authorization
-void user_access(const httplib::Request& request, httplib::Response& response) {
+void user_access(const httplib::Request &request, httplib::Response &response) {
     std::cout << GREEN << request.path << RESET << "  " << request.method << std::endl;
     response.set_header("Access-Control-Allow-Origin", "*");
-    if (request.body == "") {response.set_content("{\"required\":\"[token]\"}", "application/json");return;}
+    if (request.body.empty()) {
+        response.set_content(ACCESS_REQUIRED_STRING, JSON_TYPE);
+        return;
+    }
     nlohmann::json json_body = nlohmann::json::parse(request.body);
 
-    if (json_body["token"] == nullptr) {response.set_content("{\"required\":\"[token]\"}", "application/json");return;}
-    if (!verify_auth(json_body["token"])) {response.set_content("{\"access\":\"reject\"}", "application/json");return;}
-    response.set_content("{\"access\":\"success\"}", "application/json");
+    if (json_body["token"] == nullptr) {
+        response.set_content(ACCESS_REQUIRED_STRING, JSON_TYPE);
+        return;
+    }
+    if (!verify_auth(json_body["token"])) {
+        response.set_content(R"({"access":"reject"})", JSON_TYPE);
+        return;
+    }
+    response.set_content(R"({"access":"success"})", JSON_TYPE);
 }
diff --git a/src/users/add_user.cpp b/src/users/add_user.cpp
index 725d378..dffa784 100644
--- a/src/users/add_user.cpp
+++ b/src/users/add_user.cpp
@@ -1,68 +1,101 @@
 #include "users.hpp"
 #include "../colors.h"
+#include "../includes.hpp"
+#include "../auth/auth.hpp"
+#include <jwt-cpp/jwt.h>
 
 #define ALPHABET "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
 
 // function for generate random string
 std::string get_random_string(const char *alphabet, int quantity) {
-    srand(time(NULL));
+    srand(time(nullptr));
     std::string str;
     for (int i = 0; i < quantity; i++) {
-        str += alphabet[0 + rand() % strlen(alphabet)];
+        str += alphabet[0 + std::rand() % strlen(alphabet)];
     }
     return str;
 }
 
 // function for add user
-void add_user(const httplib::Request& request, httplib::Response& response) {
+void add_user(const httplib::Request &request, httplib::Response &response) {
     std::cout << GREEN << request.path << RESET << "  " << request.method << std::endl;
     response.set_header("Access-Control-Allow-Origin", "*");
-    if (request.body == "") {response.set_content("{\"required\":\"[token,username,password]\",\"optional\":\"[group,is_superuser]\"}", "application/json");return;}
+    if (request.body.empty()) {
+        response.set_content(ADD_USER_REQUIRED_STRING,
+                             JSON_TYPE);
+        return;
+    }
     nlohmann::json json_body = nlohmann::json::parse(request.body);
 
-    if (json_body["token"] == nullptr) {response.set_content("{\"required\":\"[token,username,password]\",\"optional\":\"[group,is_superuser]\"}", "application/json");return;}
-    if (!verify_auth(json_body["token"])) {response.set_content("{\"status\":\"403\"}", "application/json");return;}
-    if (json_body["username"] == nullptr) {response.set_content("{\"required\":\"[token,username,password]\",\"optional\":\"[group,is_superuser]\"}", "application/json");return;}
-    if (json_body["password"] == nullptr) {response.set_content("{\"required\":\"[token,username,password]\",\"optional\":\"[group,is_superuser]\"}", "application/json");return;}
+    if (json_body["token"] == nullptr) {
+        response.set_content(ADD_USER_REQUIRED_STRING,
+                             JSON_TYPE);
+        return;
+    }
+    if (!verify_auth(json_body["token"])) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
+    if (json_body["username"] == nullptr) {
+        response.set_content(ADD_USER_REQUIRED_STRING,
+                             JSON_TYPE);
+        return;
+    }
+    if (json_body["password"] == nullptr) {
+        response.set_content(ADD_USER_REQUIRED_STRING,
+                             JSON_TYPE);
+        return;
+    }
 
     jwt::decoded_jwt<jwt::traits::kazuho_picojson> decoded_token = jwt::decode(json_body["token"]);
-    std::string userid = "";
-    for (auto& e : decoded_token.get_payload_json()) {
+    std::string userid;
+    for (std::pair<const std::string, picojson::value> &e: decoded_token.get_payload_json()) {
         if (e.first == "userId") {
             userid = e.second.to_str();
             break;
         }
     }
-    if (userid == "") {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    if (userid.empty()) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
 
     std::ifstream usersfile("users.json");
     nlohmann::json all_users = nlohmann::json::parse(usersfile);
     usersfile.close();
 
     nlohmann::json response_user_data = nullptr;
-    for (nlohmann::json& user : all_users) {
+    for (nlohmann::json &user: all_users) {
         if (user["id"] == userid) {
             response_user_data = user;
         }
     }
-    if (response_user_data == nullptr) {response.set_content("{\"status\":\"403\"}", "application/json");return;}
-    if (response_user_data["is_superuser"] != "1") {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    if (response_user_data == nullptr) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
+    if (response_user_data["is_superuser"] != "1") {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
 
     const std::string username = json_body["username"];
     const std::string password = json_body["password"];
 
-    for (nlohmann::json user : all_users) {
+    for (nlohmann::json user: all_users) {
         if ((user["username"] == username)) {
-            response.set_content("{\"status\":\"user already exists\"}", "application/json");return;
+            response.set_content(R"({"status":"user already exists"})", JSON_TYPE);
+            return;
         }
     }
 
     std::stringstream new_user_data;
 
-    new_user_data << "{\"id\":\"" << get_random_string(ALPHABET, 50) << "\",\"username\":\"" << username << "\",\"password\":\"" << password << "\",\"group\":";
+    new_user_data << R"({"id":")" << get_random_string(ALPHABET, 50) << R"(","username":")"
+            << username << R"(","password":")" << password << R"(","group":)";
     (json_body["group"] != nullptr) ? new_user_data << json_body["group"] : new_user_data << "\"users\"";
     new_user_data << ",\"is_superuser\":";
-    (json_body["is_superuser"]  != nullptr) ? new_user_data << json_body["is_superuser"] : new_user_data << "\"0\"";
+    (json_body["is_superuser"] != nullptr) ? new_user_data << json_body["is_superuser"] : new_user_data << "\"0\"";
     new_user_data << "}";
     all_users.push_back(nlohmann::json::parse(new_user_data));
 
@@ -70,5 +103,5 @@ void add_user(const httplib::Request& request, httplib::Response& response) {
     usersfilew << all_users.dump(4);
     usersfilew.close();
 
-    response.set_content("{\"status\":\"ok\"}", "application/json");
+    response.set_content(R"({"status":"ok"})", JSON_TYPE);
 }
diff --git a/src/users/change_password.cpp b/src/users/change_password.cpp
index 84fdf58..7418019 100644
--- a/src/users/change_password.cpp
+++ b/src/users/change_password.cpp
@@ -1,41 +1,62 @@
 #include "users.hpp"
 #include "../colors.h"
+#include "../includes.hpp"
+#include "../auth/auth.hpp"
+#include <jwt-cpp/jwt.h>
 
 // functtion for change password for user
-void change_password(const httplib::Request& request, httplib::Response& response) {
+void change_password(const httplib::Request &request, httplib::Response &response) {
     std::cout << GREEN << request.path << RESET << "  " << request.method << std::endl;
     response.set_header("Access-Control-Allow-Origin", "*");
-    if (request.body == "") {response.set_content(
-        "{\"required\":\"[token,old_password,new_password] or if you superuser [token,userid,new_password]\"}", 
-        "application/json"
-    );return;}
-    nlohmann::json json_body = nlohmann::json::parse(request.body);
-
-    if (json_body["token"] == nullptr) {response.set_content(
-        "{\"required\":\"[token,old_password,new_password] or if you superuser [token,userid,new_password]\"}", 
-        "application/json"
-    );return;}
-    if ((json_body["userid"] == nullptr) && (json_body["old_password"] == nullptr)) {
-        response.set_content("{\"required\":\"[token,old_password,new_password] or if you superuser [token,userid,new_password]\"}", "application/json");
+    if (request.body.empty()) {
+        response.set_content(
+            CHANGE_PASSWORD_REQUIRED_STRING,
+            JSON_TYPE
+        );
         return;
     }
-    if (json_body["new_password"] == nullptr) {response.set_content("{\"required\":\"[token] or if you superuser [token,userid]\"}", "application/json");return;}
-    if (!verify_auth(json_body["token"])) {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    nlohmann::json json_body = nlohmann::json::parse(request.body);
 
-    std::string old_password = "";
+    if (json_body["token"] == nullptr) {
+        response.set_content(
+            CHANGE_PASSWORD_REQUIRED_STRING,
+            JSON_TYPE
+        );
+        return;
+    }
+    if ((json_body["userid"] == nullptr) && (json_body["old_password"] == nullptr)) {
+        response.set_content(
+            CHANGE_PASSWORD_REQUIRED_STRING,
+            JSON_TYPE);
+        return;
+    }
+    if (json_body["new_password"] == nullptr) {
+        response.set_content(R"({"required":"[token] or if you superuser [token,userid]"})",
+                             JSON_TYPE);
+        return;
+    }
+    if (!verify_auth(json_body["token"])) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
+
+    std::string old_password;
     const std::string new_password = json_body["new_password"];
 
-    if (json_body["userid"] == nullptr) {old_password = json_body["old_password"];}
+    if (json_body["userid"] == nullptr) { old_password = json_body["old_password"]; }
 
     jwt::decoded_jwt<jwt::traits::kazuho_picojson> decoded_token = jwt::decode(json_body["token"]);
-    std::string userid = "";
-    for (auto& e : decoded_token.get_payload_json()) {
+    std::string userid;
+    for (std::pair<const std::string, picojson::value> &e: decoded_token.get_payload_json()) {
         if (e.first == "userId") {
             userid = e.second.to_str();
             break;
         }
     }
-    if (userid == "") {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    if (userid.empty()) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
 
     std::ifstream usersfile("users.json");
     nlohmann::json all_users = nlohmann::json::parse(usersfile);
@@ -45,36 +66,45 @@ void change_password(const httplib::Request& request, httplib::Response& respons
     if (json_body["userid"] != nullptr) {
         changepassuserid = json_body["userid"];
         nlohmann::json response_user_data = nullptr;
-        for (nlohmann::json& user : all_users) {
+        for (nlohmann::json &user: all_users) {
             if (user["id"] == userid) {
                 response_user_data = user;
             }
         }
-        if (response_user_data == nullptr) {response.set_content("{\"status\":\"403\"}", "application/json");return;}
-        if (response_user_data["is_superuser"] != "1") {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+        if (response_user_data == nullptr) {
+            response.set_content(STRING403, JSON_TYPE);
+            return;
+        }
+        if (response_user_data["is_superuser"] != "1") {
+            response.set_content(STRING403, JSON_TYPE);
+            return;
+        }
     }
 
     bool found = false;
     if (json_body["userid"] != nullptr) {
-        for (int i = 0; i < all_users.size(); i++) {
-            if ((all_users[i]["id"] == changepassuserid)) {
-                all_users[i]["password"] = new_password;
+        for (nlohmann::basic_json<> &all_user: all_users) {
+            if ((all_user["id"] == changepassuserid)) {
+                all_user["password"] = new_password;
                 found = true;
                 break;
             }
         }
     } else {
-        for (int i = 0; i < all_users.size(); i++) {
-            if ((all_users[i]["id"] == changepassuserid) && (all_users[i]["password"] == old_password)) {
-                all_users[i]["password"] = new_password;
+        for (nlohmann::basic_json<> &all_user: all_users) {
+            if ((all_user["id"] == changepassuserid) && (all_user["password"] == old_password)) {
+                all_user["password"] = new_password;
                 found = true;
                 break;
             }
         }
     }
-    if (!found) {response.set_content("{\"status\":\"can't find this user\"}", "application/json");return;}
+    if (!found) {
+        response.set_content(R"({"status":"can't find this user"})", JSON_TYPE);
+        return;
+    }
     std::ofstream usersfilew("users.json");
     usersfilew << all_users.dump(4);
     usersfilew.close();
-    response.set_content("{\"status\":\"ok\"}", "application/json");
+    response.set_content(R"({"status":"ok"})", JSON_TYPE);
 }
diff --git a/src/users/change_user.cpp b/src/users/change_user.cpp
index 854cc14..ec6b665 100644
--- a/src/users/change_user.cpp
+++ b/src/users/change_user.cpp
@@ -1,41 +1,51 @@
 #include "users.hpp"
 #include "../colors.h"
+#include "../includes.hpp"
+#include "../auth/auth.hpp"
+#include <jwt-cpp/jwt.h>
 
 // function for change user data
-void change_user(const httplib::Request& request, httplib::Response& response) {
+void change_user(const httplib::Request &request, httplib::Response &response) {
     std::cout << GREEN << request.path << RESET << "  " << request.method << std::endl;
     response.set_header("Access-Control-Allow-Origin", "*");
-    if (request.body == "") {response.set_content(
-        "{\"required\":\"[token] or if you superuser [token,userid]\",\"optional\":\"[username,password,is_superuser,group]\"}", 
-        "application/json"
-    );return;}
-    nlohmann::json json_body = nlohmann::json::parse(request.body);
-
-    if (json_body["token"] == nullptr) {response.set_content(
-        "{\"required\":\"[token] or if you superuser [token,userid]\",\"optional\":\"[username,password,is_superuser,group]\"}", 
-        "application/json"
-    );return;}
-    if ((json_body["userid"] == nullptr) && (json_body["old_password"] == nullptr)) {
-        response.set_content("{\"required\":\"[token] or if you superuser [token,userid]\",\"optional\":\"[username,password,is_superuser,group]\"}", "application/json");
+    if (request.body.empty()) {
+        response.set_content(
+            CHANGE_USER_REQUIRED_STRING,
+            JSON_TYPE);
         return;
     }
-    // if (json_body["new_password"] == nullptr) {response.set_content("{\"required\":\"[token] or if you superuser [token,userid]\"}", "application/json");return;}
-    if (!verify_auth(json_body["token"])) {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    nlohmann::json json_body = nlohmann::json::parse(request.body);
 
-    // std::string old_password = "";
-    // const std::string new_password = json_body["new_password"];
-
-    // if (json_body["userid"] == nullptr) {old_password = json_body["old_password"];}
+    if (json_body["token"] == nullptr) {
+        response.set_content(
+            CHANGE_USER_REQUIRED_STRING,
+            JSON_TYPE
+        );
+        return;
+    }
+    if ((json_body["userid"] == nullptr) && (json_body["old_password"] == nullptr)) {
+        response.set_content(
+            CHANGE_USER_REQUIRED_STRING,
+            JSON_TYPE);
+        return;
+    }
+    if (!verify_auth(json_body["token"])) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
 
     jwt::decoded_jwt<jwt::traits::kazuho_picojson> decoded_token = jwt::decode(json_body["token"]);
-    std::string userid = "";
-    for (auto& e : decoded_token.get_payload_json()) {
+    std::string userid;
+    for (std::pair<const std::string, picojson::value> &e: decoded_token.get_payload_json()) {
         if (e.first == "userId") {
             userid = e.second.to_str();
             break;
         }
     }
-    if (userid == "") {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    if (userid.empty()) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
 
     std::ifstream usersfile("users.json");
     nlohmann::json all_users = nlohmann::json::parse(usersfile);
@@ -45,40 +55,48 @@ void change_user(const httplib::Request& request, httplib::Response& response) {
     if (json_body["userid"] != nullptr) {
         changeusruserid = json_body["userid"];
         nlohmann::json response_user_data = nullptr;
-        for (nlohmann::json& user : all_users) {
+        for (nlohmann::json &user: all_users) {
             if (user["id"] == userid) {
                 response_user_data = user;
             }
         }
-        if (response_user_data == nullptr) {response.set_content("{\"status\":\"403\"}", "application/json");return;}
-        if (response_user_data["is_superuser"] != "1") {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+        if (response_user_data == nullptr) {
+            response.set_content(STRING403, JSON_TYPE);
+            return;
+        }
+        if (response_user_data["is_superuser"] != "1") {
+            response.set_content(STRING403, JSON_TYPE);
+            return;
+        }
     }
 
     bool found = false;
     if (json_body["userid"] != nullptr) {
-        for (int i = 0; i < all_users.size(); i++) {
-            if ((all_users[i]["id"] == changeusruserid)) {
-                if (json_body["username"] != nullptr) {all_users[i]["username"] = json_body["username"];}
-                if (json_body["password"] != nullptr) {all_users[i]["password"] = json_body["password"];}
-                if (json_body["group"] != nullptr) {all_users[i]["group"] = json_body["group"];}
-                if (json_body["is_superuser"] != nullptr) {all_users[i]["is_superuser"] = json_body["is_superuser"];}
+        for (nlohmann::basic_json<> &all_user: all_users) {
+            if ((all_user["id"] == changeusruserid)) {
+                if (json_body["username"] != nullptr) { all_user["username"] = json_body["username"]; }
+                if (json_body["password"] != nullptr) { all_user["password"] = json_body["password"]; }
+                if (json_body["group"] != nullptr) { all_user["group"] = json_body["group"]; }
+                if (json_body["is_superuser"] != nullptr) { all_user["is_superuser"] = json_body["is_superuser"]; }
                 found = true;
                 break;
             }
         }
     } else {
-        for (int i = 0; i < all_users.size(); i++) {
-            if ((all_users[i]["id"] == changeusruserid)) {
-                if (json_body["username"] != nullptr) {all_users[i]["username"] = json_body["username"];}
+        for (nlohmann::basic_json<> &all_user: all_users) {
+            if ((all_user["id"] == changeusruserid)) {
+                if (json_body["username"] != nullptr) { all_user["username"] = json_body["username"]; }
                 found = true;
                 break;
             }
         }
     }
-    if (!found) {response.set_content("{\"status\":\"can't find this user\"}", "application/json");return;}
+    if (!found) {
+        response.set_content(R"({"status":"can't find this user"})", JSON_TYPE);
+        return;
+    }
     std::ofstream usersfilew("users.json");
     usersfilew << all_users.dump(4);
     usersfilew.close();
-    response.set_content("{\"status\":\"ok\"}", "application/json");
+    response.set_content(R"({"status":"ok"})", JSON_TYPE);
 }
-
diff --git a/src/users/delete_user.cpp b/src/users/delete_user.cpp
index b45ecc5..4a74d16 100644
--- a/src/users/delete_user.cpp
+++ b/src/users/delete_user.cpp
@@ -1,25 +1,44 @@
 #include "users.hpp"
 #include "../colors.h"
+#include "../includes.hpp"
+#include "../auth/auth.hpp"
+#include <jwt-cpp/jwt.h>
 
 // function for delete user
-void delete_user(const httplib::Request& request, httplib::Response& response) {
+void delete_user(const httplib::Request &request, httplib::Response &response) {
     std::cout << GREEN << request.path << RESET << "  " << request.method << std::endl;
     response.set_header("Access-Control-Allow-Origin", "*");
-    if (request.body == "") {response.set_content("{\"required\":\"[token] or if you superuser [token,userid]\"}", "application/json");return;}
+    if (request.body.empty()) {
+        response.set_content(
+            DELETE_USER_REQUIRED_STRING,
+            JSON_TYPE);
+        return;
+    }
     nlohmann::json json_body = nlohmann::json::parse(request.body);
 
-    if (json_body["token"] == nullptr) {response.set_content("{\"required\":\"[token] or if you superuser [token,userid]\"}", "application/json");return;}
-    if (!verify_auth(json_body["token"])) {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    if (json_body["token"] == nullptr) {
+        response.set_content(
+            DELETE_USER_REQUIRED_STRING,
+            JSON_TYPE);
+        return;
+    }
+    if (!verify_auth(json_body["token"])) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
 
     jwt::decoded_jwt<jwt::traits::kazuho_picojson> decoded_token = jwt::decode(json_body["token"]);
-    std::string userid = "";
-    for (auto& e : decoded_token.get_payload_json()) {
+    std::string userid;
+    for (std::pair<const std::string, picojson::value> &e: decoded_token.get_payload_json()) {
         if (e.first == "userId") {
             userid = e.second.to_str();
             break;
         }
     }
-    if (userid == "") {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    if (userid.empty()) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
 
     std::ifstream usersfile("users.json");
     nlohmann::json all_users = nlohmann::json::parse(usersfile);
@@ -29,13 +48,19 @@ void delete_user(const httplib::Request& request, httplib::Response& response) {
     if (json_body["userid"] != nullptr) {
         deluserid = json_body["userid"];
         nlohmann::json response_user_data = nullptr;
-        for (nlohmann::json& user : all_users) {
+        for (nlohmann::json &user: all_users) {
             if (user["id"] == userid) {
                 response_user_data = user;
             }
         }
-        if (response_user_data == nullptr) {response.set_content("{\"status\":\"403\"}", "application/json");return;}
-        if (response_user_data["is_superuser"] != "1") {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+        if (response_user_data == nullptr) {
+            response.set_content(STRING403, JSON_TYPE);
+            return;
+        }
+        if (response_user_data["is_superuser"] != "1") {
+            response.set_content(STRING403, JSON_TYPE);
+            return;
+        }
     }
 
     bool found = false;
@@ -46,9 +71,12 @@ void delete_user(const httplib::Request& request, httplib::Response& response) {
             break;
         }
     }
-    if (!found) {response.set_content("{\"status\":\"can't find this user\"}", "application/json");return;}
+    if (!found) {
+        response.set_content(R"({"status":"can't find this user"})", JSON_TYPE);
+        return;
+    }
     std::ofstream usersfilew("users.json");
     usersfilew << all_users.dump(4);
     usersfilew.close();
-    response.set_content("{\"status\":\"ok\"}", "application/json");
+    response.set_content(R"({"status":"ok"})", JSON_TYPE);
 }
diff --git a/src/users/get_all_users.cpp b/src/users/get_all_users.cpp
index 00c09d3..b20650e 100644
--- a/src/users/get_all_users.cpp
+++ b/src/users/get_all_users.cpp
@@ -1,35 +1,56 @@
 #include "users.hpp"
 #include "../colors.h"
+#include "../includes.hpp"
+#include "../auth/auth.hpp"
+#include <jwt-cpp/jwt.h>
 
 // function for get all users data without password
-void get_all_users(const httplib::Request& request, httplib::Response& response) {
+void get_all_users(const httplib::Request &request, httplib::Response &response) {
     std::cout << GREEN << request.path << RESET << "  " << request.method << std::endl;
     response.set_header("Access-Control-Allow-Origin", "*");
-    if (request.body == "") {response.set_content("{\"required\":\"[token]\"}", "application/json");return;}
+    if (request.body.empty()) {
+        response.set_content(ACCESS_REQUIRED_STRING, JSON_TYPE);
+        return;
+    }
     nlohmann::json json_body = nlohmann::json::parse(request.body);
 
-    if (json_body["token"] == nullptr) {response.set_content("{\"required\":\"[token]\"}", "application/json");return;}
-    if (!verify_auth(json_body["token"])) {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    if (json_body["token"] == nullptr) {
+        response.set_content(ACCESS_REQUIRED_STRING, JSON_TYPE);
+        return;
+    }
+    if (!verify_auth(json_body["token"])) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
     jwt::decoded_jwt<jwt::traits::kazuho_picojson> decoded_token = jwt::decode(json_body["token"]);
-    std::string userid = "";
-    for (auto& e : decoded_token.get_payload_json()) {
+    std::string userid;
+    for (std::pair<const std::string, picojson::value> &e: decoded_token.get_payload_json()) {
         if (e.first == "userId") {
             userid = e.second.to_str();
             break;
         }
     }
-    if (userid == "") {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    if (userid.empty()) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
     std::ifstream usersfile("users.json");
     nlohmann::json all_users = nlohmann::json::parse(usersfile);
     usersfile.close();
     nlohmann::json response_user_data = nullptr;
-    for (nlohmann::json& user : all_users) {
+    for (nlohmann::json &user: all_users) {
         if (user["id"] == userid) {
             response_user_data = user;
         }
         user.erase("password");
     }
-    if (response_user_data == nullptr) {response.set_content("{\"status\":\"403\"}", "application/json");return;}
-    if (response_user_data["is_superuser"] != "1") {response.set_content("{\"status\":\"403\"}", "application/json");return;}
-    response.set_content(all_users.dump(), "application/json");
+    if (response_user_data == nullptr) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
+    if (response_user_data["is_superuser"] != "1") {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
+    response.set_content(all_users.dump(), JSON_TYPE);
 }
diff --git a/src/users/get_user.cpp b/src/users/get_user.cpp
index 42f5dce..b17ce99 100644
--- a/src/users/get_user.cpp
+++ b/src/users/get_user.cpp
@@ -1,35 +1,53 @@
 #include "users.hpp"
 #include "../colors.h"
+#include "../includes.hpp"
+#include "../auth/auth.hpp"
+#include <jwt-cpp/jwt.h>
 
 // function for get user data without password
-void get_user(const httplib::Request& request, httplib::Response& response) {
+void get_user(const httplib::Request &request, httplib::Response &response) {
     std::cout << GREEN << request.path << RESET << "  " << request.method << std::endl;
     response.set_header("Access-Control-Allow-Origin", "*");
-    if (request.body == "") {response.set_content("{\"required\":\"[token]\"}", "application/json");return;}
+    if (request.body.empty()) {
+        response.set_content(ACCESS_REQUIRED_STRING, JSON_TYPE);
+        return;
+    }
     nlohmann::json json_body = nlohmann::json::parse(request.body);
 
-    if (json_body["token"] == nullptr) {response.set_content("{\"required\":\"[token]\"}", "application/json");return;}
-    if (!verify_auth(json_body["token"])) {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    if (json_body["token"] == nullptr) {
+        response.set_content(ACCESS_REQUIRED_STRING, JSON_TYPE);
+        return;
+    }
+    if (!verify_auth(json_body["token"])) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
     jwt::decoded_jwt<jwt::traits::kazuho_picojson> decoded_token = jwt::decode(json_body["token"]);
-    std::string userid = "";
-    for (auto& e : decoded_token.get_payload_json()) {
+    std::string userid;
+    for (std::pair<const std::string, picojson::value> &e: decoded_token.get_payload_json()) {
         if (e.first == "userId") {
             userid = e.second.to_str();
             break;
         }
     }
-    if (userid == "") {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    if (userid.empty()) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
     std::ifstream usersfile("users.json");
     nlohmann::json all_users = nlohmann::json::parse(usersfile);
     usersfile.close();
     nlohmann::json response_user_data = nullptr;
-    for (nlohmann::json& user : all_users) {
+    for (nlohmann::json &user: all_users) {
         if (user["id"] == userid) {
             response_user_data = user;
             break;
         }
     }
-    if (response_user_data == nullptr) {response.set_content("{\"status\":\"403\"}", "application/json");return;}
+    if (response_user_data == nullptr) {
+        response.set_content(STRING403, JSON_TYPE);
+        return;
+    }
     response_user_data.erase("password");
-    response.set_content(response_user_data.dump(), "application/json");
+    response.set_content(response_user_data.dump(), JSON_TYPE);
 }
diff --git a/src/users/users.hpp b/src/users/users.hpp
index bcf386f..c1208f4 100644
--- a/src/users/users.hpp
+++ b/src/users/users.hpp
@@ -2,22 +2,26 @@
 #define USERS_HPP
 
 #include <httplib.h>
-#include <json.hpp>
-#include "../auth/auth.hpp"
 
 // function for get user data without password
-void get_user(const httplib::Request& request, httplib::Response& response);
+void get_user(const httplib::Request &request, httplib::Response &response);
+
 // function for get all users data without password
-void get_all_users(const httplib::Request& request, httplib::Response& response);
+void get_all_users(const httplib::Request &request, httplib::Response &response);
+
 // function for access or reject authorization
-void user_access(const httplib::Request& request, httplib::Response& response);
+void user_access(const httplib::Request &request, httplib::Response &response);
+
 // function for add user
-void add_user(const httplib::Request& request, httplib::Response& response);
+void add_user(const httplib::Request &request, httplib::Response &response);
+
 // function for delete user
-void delete_user(const httplib::Request& request, httplib::Response& response);
+void delete_user(const httplib::Request &request, httplib::Response &response);
+
 // function for change password for user
-void change_password(const httplib::Request& request, httplib::Response& response);
+void change_password(const httplib::Request &request, httplib::Response &response);
+
 // function for change user data
-void change_user(const httplib::Request& request, httplib::Response& response);
+void change_user(const httplib::Request &request, httplib::Response &response);
 
 #endif // USERS_HPP