diff --git a/app/src/main/java/ru/dragonestia/picker/controller/UserController.java b/app/src/main/java/ru/dragonestia/picker/controller/UserController.java
index bac8bab..1afe677 100644
--- a/app/src/main/java/ru/dragonestia/picker/controller/UserController.java
+++ b/app/src/main/java/ru/dragonestia/picker/controller/UserController.java
@@ -5,11 +5,10 @@ import io.swagger.v3.oas.annotations.Parameter;
 import io.swagger.v3.oas.annotations.tags.Tag;
 import lombok.RequiredArgsConstructor;
 import org.springframework.web.bind.annotation.*;
+import ru.dragonestia.picker.api.model.user.ResponseUser;
 import ru.dragonestia.picker.api.repository.response.LinkedRoomsWithUserResponse;
 import ru.dragonestia.picker.api.repository.response.SearchUserResponse;
 import ru.dragonestia.picker.api.repository.response.UserDetailsResponse;
-import ru.dragonestia.picker.api.repository.response.type.RUser;
-import ru.dragonestia.picker.model.Room;
 import ru.dragonestia.picker.model.User;
 import ru.dragonestia.picker.service.UserService;
 import ru.dragonestia.picker.util.DetailsParser;
@@ -47,7 +46,7 @@ public class UserController {
             @Parameter(description = "Required addition user data", example = "COUNT_ROOMS") @RequestParam(value = "requiredDetails", required = false) String detailsSeq
     ) {
         if (!namingValidator.validateUserId(userId)) {
-            return new UserDetailsResponse(new RUser(userId));
+            return new UserDetailsResponse(new ResponseUser(userId));
         }
 
         return new UserDetailsResponse(userService.getUserDetails(userId, detailsParser.parseUserDetails(detailsSeq)));
diff --git a/app/src/main/java/ru/dragonestia/picker/model/User.java b/app/src/main/java/ru/dragonestia/picker/model/User.java
index 9848007..f28f5c7 100644
--- a/app/src/main/java/ru/dragonestia/picker/model/User.java
+++ b/app/src/main/java/ru/dragonestia/picker/model/User.java
@@ -1,7 +1,7 @@
 package ru.dragonestia.picker.model;
 
 import lombok.NonNull;
-import ru.dragonestia.picker.api.repository.response.type.RUser;
+import ru.dragonestia.picker.api.model.user.ResponseUser;
 
 public record User(@NonNull String id) {
 
@@ -20,7 +20,7 @@ public record User(@NonNull String id) {
         return false;
     }
 
-    public RUser toResponseObject() {
-        return new RUser(id);
+    public ResponseUser toResponseObject() {
+        return new ResponseUser(id);
     }
 }
diff --git a/app/src/main/java/ru/dragonestia/picker/service/UserService.java b/app/src/main/java/ru/dragonestia/picker/service/UserService.java
index 8751bc6..00e843c 100644
--- a/app/src/main/java/ru/dragonestia/picker/service/UserService.java
+++ b/app/src/main/java/ru/dragonestia/picker/service/UserService.java
@@ -3,8 +3,8 @@ package ru.dragonestia.picker.service;
 import ru.dragonestia.picker.api.exception.RoomAreFullException;
 import ru.dragonestia.picker.api.model.room.RoomDetails;
 import ru.dragonestia.picker.api.model.room.ShortResponseRoom;
+import ru.dragonestia.picker.api.model.user.ResponseUser;
 import ru.dragonestia.picker.api.model.user.UserDetails;
-import ru.dragonestia.picker.api.repository.response.type.RUser;
 import ru.dragonestia.picker.model.Room;
 import ru.dragonestia.picker.model.User;
 
@@ -24,9 +24,9 @@ public interface UserService {
 
     List<User> getRoomUsers(Room room);
 
-    List<RUser> getRoomUsersWithDetailsResponse(Room room, Set<UserDetails> details);
+    List<ResponseUser> getRoomUsersWithDetailsResponse(Room room, Set<UserDetails> details);
 
-    List<RUser> searchUsers(String input, Set<UserDetails> details);
+    List<ResponseUser> searchUsers(String input, Set<UserDetails> details);
 
-    RUser getUserDetails(String userId, Set<UserDetails> details);
+    ResponseUser getUserDetails(String userId, Set<UserDetails> details);
 }
diff --git a/app/src/main/java/ru/dragonestia/picker/service/impl/UserServiceImpl.java b/app/src/main/java/ru/dragonestia/picker/service/impl/UserServiceImpl.java
index a6f42ab..ad9c1cb 100644
--- a/app/src/main/java/ru/dragonestia/picker/service/impl/UserServiceImpl.java
+++ b/app/src/main/java/ru/dragonestia/picker/service/impl/UserServiceImpl.java
@@ -4,8 +4,8 @@ import lombok.RequiredArgsConstructor;
 import org.springframework.stereotype.Service;
 import ru.dragonestia.picker.api.model.room.RoomDetails;
 import ru.dragonestia.picker.api.model.room.ShortResponseRoom;
+import ru.dragonestia.picker.api.model.user.ResponseUser;
 import ru.dragonestia.picker.api.model.user.UserDetails;
-import ru.dragonestia.picker.api.repository.response.type.RUser;
 import ru.dragonestia.picker.model.Room;
 import ru.dragonestia.picker.model.User;
 import ru.dragonestia.picker.repository.UserRepository;
@@ -52,8 +52,8 @@ public class UserServiceImpl implements UserService {
     }
 
     @Override
-    public List<RUser> getRoomUsersWithDetailsResponse(Room room, Set<UserDetails> details) {
-        var users = new LinkedList<RUser>();
+    public List<ResponseUser> getRoomUsersWithDetailsResponse(Room room, Set<UserDetails> details) {
+        var users = new LinkedList<ResponseUser>();
         for (var user: getRoomUsers(room)) {
             users.add(detailsExtractor.extract(user, details));
         }
@@ -61,12 +61,12 @@ public class UserServiceImpl implements UserService {
     }
 
     @Override
-    public List<RUser> searchUsers(String input, Set<UserDetails> details) {
+    public List<ResponseUser> searchUsers(String input, Set<UserDetails> details) {
         return userRepository.search(input).stream().map(user -> detailsExtractor.extract(user, details)).toList();
     }
 
     @Override
-    public RUser getUserDetails(String userId, Set<UserDetails> details) {
+    public ResponseUser getUserDetails(String userId, Set<UserDetails> details) {
         return detailsExtractor.extract(new User(userId), details);
     }
 }
diff --git a/app/src/main/java/ru/dragonestia/picker/util/DetailsExtractor.java b/app/src/main/java/ru/dragonestia/picker/util/DetailsExtractor.java
index 860b0e6..7bad143 100644
--- a/app/src/main/java/ru/dragonestia/picker/util/DetailsExtractor.java
+++ b/app/src/main/java/ru/dragonestia/picker/util/DetailsExtractor.java
@@ -6,8 +6,8 @@ import ru.dragonestia.picker.api.model.node.NodeDetails;
 import ru.dragonestia.picker.api.model.node.ResponseNode;
 import ru.dragonestia.picker.api.model.room.RoomDetails;
 import ru.dragonestia.picker.api.model.room.ShortResponseRoom;
+import ru.dragonestia.picker.api.model.user.ResponseUser;
 import ru.dragonestia.picker.api.model.user.UserDetails;
-import ru.dragonestia.picker.api.repository.response.type.RUser;
 import ru.dragonestia.picker.model.Node;
 import ru.dragonestia.picker.model.Room;
 import ru.dragonestia.picker.model.User;
@@ -57,7 +57,7 @@ public class DetailsExtractor {
         return response;
     }
 
-    public RUser extract(User user, Set<UserDetails> details) {
+    public ResponseUser extract(User user, Set<UserDetails> details) {
         var response = user.toResponseObject();
 
         for (var detail: details) {
diff --git a/client-api/src/main/java/ru/dragonestia/picker/api/model/user/IUser.java b/client-api/src/main/java/ru/dragonestia/picker/api/model/user/IUser.java
index 5279b5d..89ff2c5 100644
--- a/client-api/src/main/java/ru/dragonestia/picker/api/model/user/IUser.java
+++ b/client-api/src/main/java/ru/dragonestia/picker/api/model/user/IUser.java
@@ -1,4 +1,11 @@
 package ru.dragonestia.picker.api.model.user;
 
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
 public interface IUser {
+
+    @NotNull String getIdentifier();
+
+    @Nullable String getDetail(@NotNull UserDetails detail);
 }
diff --git a/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/type/RUser.java b/client-api/src/main/java/ru/dragonestia/picker/api/model/user/ResponseUser.java
similarity index 51%
rename from client-api/src/main/java/ru/dragonestia/picker/api/repository/response/type/RUser.java
rename to client-api/src/main/java/ru/dragonestia/picker/api/model/user/ResponseUser.java
index 85990af..0086ceb 100644
--- a/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/type/RUser.java
+++ b/client-api/src/main/java/ru/dragonestia/picker/api/model/user/ResponseUser.java
@@ -1,41 +1,42 @@
-package ru.dragonestia.picker.api.repository.response.type;
+package ru.dragonestia.picker.api.model.user;
 
 import io.swagger.v3.oas.annotations.media.Schema;
-import ru.dragonestia.picker.api.model.user.UserDetails;
+import org.jetbrains.annotations.ApiStatus.Internal;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.HashMap;
 import java.util.Map;
 
 @Schema(title = "User")
-public class RUser {
+public class ResponseUser implements IUser {
 
     @Schema(description = "User identifier", example = "test-user")
     private String id;
 
     @Schema(description = "Additional data requested (Key-Value)")
-    private Map<UserDetails, String> details = new HashMap<>();
+    private Map<UserDetails, String> details;
 
-    private RUser() {}
+    @Internal
+    public ResponseUser() {}
 
-    public RUser(String id) {
+    public ResponseUser(@NotNull String id) {
         this.id = id;
         this.details = new HashMap<>();
     }
 
-    public String getId() {
+    @Override
+    public @NotNull String getIdentifier() {
         return id;
     }
 
-    public void putDetail(UserDetails detail, String value) {
-        details.put(detail, value);
-    }
-
-    public String getDetail(UserDetails detail) {
+    @Override
+    public @Nullable String getDetail(@NotNull UserDetails detail) {
         return details.get(detail);
     }
 
-    public Map<UserDetails, String> getDetails() {
-        return details;
+    public void putDetail(@NotNull UserDetails detail, @NotNull String value) {
+        details.put(detail, value);
     }
 
     @Override
@@ -47,9 +48,14 @@ public class RUser {
     public boolean equals(Object object) {
         if (object == this) return true;
         if (object == null) return false;
-        if (object instanceof RUser other) {
+        if (object instanceof ResponseUser other) {
             return id.equals(other.id);
         }
         return false;
     }
+
+    @Override
+    public String toString() {
+        return "[ResponseUser id='%s]".formatted(id);
+    }
 }
diff --git a/client-api/src/main/java/ru/dragonestia/picker/api/model/user/UserDefinition.java b/client-api/src/main/java/ru/dragonestia/picker/api/model/user/UserDefinition.java
new file mode 100644
index 0000000..961141b
--- /dev/null
+++ b/client-api/src/main/java/ru/dragonestia/picker/api/model/user/UserDefinition.java
@@ -0,0 +1,24 @@
+package ru.dragonestia.picker.api.model.user;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+import ru.dragonestia.picker.api.repository.type.UserIdentifier;
+
+public class UserDefinition implements IUser {
+
+    private final String id;
+
+    public UserDefinition(@NotNull UserIdentifier identifier) {
+        id = identifier.getValue();
+    }
+
+    @Override
+    public @NotNull String getIdentifier() {
+        return id;
+    }
+
+    @Override
+    public @Nullable String getDetail(@NotNull UserDetails detail) {
+        throw new UnsupportedOperationException();
+    }
+}
diff --git a/client-api/src/main/java/ru/dragonestia/picker/api/repository/UserRepository.java b/client-api/src/main/java/ru/dragonestia/picker/api/repository/UserRepository.java
index 3db542e..c23a626 100644
--- a/client-api/src/main/java/ru/dragonestia/picker/api/repository/UserRepository.java
+++ b/client-api/src/main/java/ru/dragonestia/picker/api/repository/UserRepository.java
@@ -1,13 +1,10 @@
 package ru.dragonestia.picker.api.repository;
 
-import ru.dragonestia.picker.api.exception.NodeNotFoundException;
-import ru.dragonestia.picker.api.exception.RoomAreFullException;
-import ru.dragonestia.picker.api.exception.RoomNotFoundException;
 import ru.dragonestia.picker.api.model.room.ResponseRoom;
 import ru.dragonestia.picker.api.model.room.RoomDetails;
 import ru.dragonestia.picker.api.model.room.ShortResponseRoom;
+import ru.dragonestia.picker.api.model.user.ResponseUser;
 import ru.dragonestia.picker.api.model.user.UserDetails;
-import ru.dragonestia.picker.api.repository.response.type.RUser;
 
 import java.util.Collection;
 import java.util.List;
@@ -15,21 +12,15 @@ import java.util.Set;
 
 public interface UserRepository {
 
-    Set<UserDetails> ALL_DETAILS = Set.of(UserDetails.COUNT_ROOMS);
+    void linkWithRoom(ResponseRoom room, Collection<ResponseUser> users, boolean force);
 
-    void linkWithRoom(ResponseRoom room, Collection<RUser> users, boolean force) throws NodeNotFoundException, RoomNotFoundException, RoomAreFullException;
+    void unlinkFromRoom(ResponseRoom room, Collection<ResponseUser> users);
 
-    void unlinkFromRoom(ResponseRoom room, Collection<RUser> users) throws NodeNotFoundException, RoomNotFoundException;
+    List<ResponseUser> all(ResponseRoom room, Set<UserDetails> details);
 
-    default List<RUser> all(ResponseRoom room) throws NodeNotFoundException, RoomNotFoundException {
-        return all(room, Set.of());
-    }
+    List<ResponseUser> search(String input, Set<UserDetails> details);
 
-    List<RUser> all(ResponseRoom room, Set<UserDetails> details) throws NodeNotFoundException, RoomNotFoundException;
+    ResponseUser find(String userId, Set<UserDetails> details);
 
-    List<RUser> search(String input, Set<UserDetails> details);
-
-    RUser find(String userId, Set<UserDetails> details);
-
-    List<ShortResponseRoom> getLinkedRoomsWithUsers(RUser user, Set<RoomDetails> roomDetails);
+    List<ShortResponseRoom> getLinkedRoomsWithUsers(ResponseUser user, Set<RoomDetails> roomDetails);
 }
diff --git a/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/RoomUserListResponse.java b/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/RoomUserListResponse.java
index 4e4c939..808d657 100644
--- a/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/RoomUserListResponse.java
+++ b/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/RoomUserListResponse.java
@@ -1,7 +1,7 @@
 package ru.dragonestia.picker.api.repository.response;
 
 import io.swagger.v3.oas.annotations.media.Schema;
-import ru.dragonestia.picker.api.repository.response.type.RUser;
+import ru.dragonestia.picker.api.model.user.ResponseUser;
 
 import java.util.List;
 
@@ -9,5 +9,5 @@ import java.util.List;
 public record RoomUserListResponse(
         @Schema(description = "Number of users in room", example = "15") int slots,
         @Schema(description = "Maximum number of users in room", example = "20") int usedSlots,
-        @Schema(description = "Users") List<RUser> users
+        @Schema(description = "Users") List<ResponseUser> users
 ) {}
diff --git a/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/SearchUserResponse.java b/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/SearchUserResponse.java
index 4565a70..1f3d87a 100644
--- a/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/SearchUserResponse.java
+++ b/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/SearchUserResponse.java
@@ -1,9 +1,9 @@
 package ru.dragonestia.picker.api.repository.response;
 
 import io.swagger.v3.oas.annotations.media.Schema;
-import ru.dragonestia.picker.api.repository.response.type.RUser;
+import ru.dragonestia.picker.api.model.user.ResponseUser;
 
 import java.util.List;
 
 @Schema(title = "Search user", hidden = true)
-public record SearchUserResponse(List<RUser> users) {}
+public record SearchUserResponse(List<ResponseUser> users) {}
diff --git a/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/UserDetailsResponse.java b/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/UserDetailsResponse.java
index b5778d8..f95f055 100644
--- a/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/UserDetailsResponse.java
+++ b/client-api/src/main/java/ru/dragonestia/picker/api/repository/response/UserDetailsResponse.java
@@ -1,7 +1,7 @@
 package ru.dragonestia.picker.api.repository.response;
 
 import io.swagger.v3.oas.annotations.media.Schema;
-import ru.dragonestia.picker.api.repository.response.type.RUser;
+import ru.dragonestia.picker.api.model.user.ResponseUser;
 
 @Schema(title = "User details", hidden = true)
-public record UserDetailsResponse(RUser user) {}
+public record UserDetailsResponse(ResponseUser user) {}
diff --git a/client-api/src/main/java/ru/dragonestia/picker/api/repository/type/UserIdentifier.java b/client-api/src/main/java/ru/dragonestia/picker/api/repository/type/UserIdentifier.java
new file mode 100644
index 0000000..6fe9b7b
--- /dev/null
+++ b/client-api/src/main/java/ru/dragonestia/picker/api/repository/type/UserIdentifier.java
@@ -0,0 +1,24 @@
+package ru.dragonestia.picker.api.repository.type;
+
+import org.jetbrains.annotations.NotNull;
+import ru.dragonestia.picker.api.util.IdentifierValidator;
+
+import java.security.InvalidParameterException;
+
+public class UserIdentifier extends ValueObject<String> {
+
+    private UserIdentifier(String value) {
+        super(value);
+    }
+
+    @Override
+    protected void validate(String value) {
+        if (IdentifierValidator.forUser(value)) return;
+
+        throw new InvalidParameterException("Invalid user identifier");
+    }
+
+    public static @NotNull UserIdentifier of(@NotNull String identifier) {
+        return new UserIdentifier(identifier);
+    }
+}