diff --git a/dotnet/AipsCore/Application/Models/Shape/Command/CreateRectangle/CreateRectangleCommandHandler.cs b/dotnet/AipsCore/Application/Models/Shape/Command/CreateRectangle/CreateRectangleCommandHandler.cs
index c03b948..d0352f8 100644
--- a/dotnet/AipsCore/Application/Models/Shape/Command/CreateRectangle/CreateRectangleCommandHandler.cs
+++ b/dotnet/AipsCore/Application/Models/Shape/Command/CreateRectangle/CreateRectangleCommandHandler.cs
@@ -1,24 +1,37 @@
 using AipsCore.Application.Abstract.Command;
 using AipsCore.Domain.Abstract;
+using AipsCore.Domain.Common.Validation;
 using AipsCore.Domain.Models.Shape.External;
 using AipsCore.Domain.Models.Shape.Sub.Rectangle;
 using AipsCore.Domain.Models.Shape.ValueObjects;
+using AipsCore.Domain.Models.User.External;
+using AipsCore.Domain.Models.User.Validation;
+using AipsCore.Domain.Models.User.ValueObjects;
+using AipsCore.Domain.Models.Whiteboard.External;
+using AipsCore.Domain.Models.Whiteboard.Validation;
+using AipsCore.Domain.Models.Whiteboard.ValueObjects;
 
 namespace AipsCore.Application.Models.Shape.Command.CreateRectangle;
 
 public class CreateRectangleCommandHandler : ICommandHandler<CreateRectangleCommand, ShapeId>
 {
     private readonly IShapeRepository _shapeRepository;
+    private readonly IWhiteboardRepository _whiteboardRepository;
+    private readonly IUserRepository _userRepository;
     private readonly IUnitOfWork _unitOfWork;
 
-    public CreateRectangleCommandHandler(IShapeRepository shapeRepository, IUnitOfWork unitOfWork)
+    public CreateRectangleCommandHandler(IShapeRepository shapeRepository, IWhiteboardRepository whiteboardRepository, IUserRepository userRepository, IUnitOfWork unitOfWork)
     {
         _shapeRepository = shapeRepository;
+        _whiteboardRepository = whiteboardRepository;
+        _userRepository = userRepository;
         _unitOfWork = unitOfWork;
     }
     
     public async Task<ShapeId> Handle(CreateRectangleCommand command, CancellationToken cancellationToken = default)
     {
+        Validate(command);
+        
         var rectangle = Rectangle.Create(
             command.WhiteboardId,
             command.AuthorId,
@@ -33,4 +46,23 @@ public class CreateRectangleCommandHandler : ICommandHandler<CreateRectangleComm
 
         return rectangle.Id;
     }
+
+    private void Validate(CreateRectangleCommand command)
+    {
+        var whiteboardId = new WhiteboardId(command.WhiteboardId);
+        var whiteboard = _whiteboardRepository.GetByIdAsync(whiteboardId).Result;
+
+        if (whiteboard is null)
+        {
+            throw new ValidationException(WhiteboardErrors.NotFound(whiteboardId));
+        }
+        
+        var authorId = new UserId(command.AuthorId);
+        var author = _userRepository.GetByIdAsync(authorId).Result;
+
+        if (author is null)
+        {
+            throw new ValidationException(UserErrors.NotFound(authorId));
+        }
+    }
 }
\ No newline at end of file
diff --git a/dotnet/AipsWebApi/Controllers/ShapeController.cs b/dotnet/AipsWebApi/Controllers/ShapeController.cs
index 4da93cc..3c85af8 100644
--- a/dotnet/AipsWebApi/Controllers/ShapeController.cs
+++ b/dotnet/AipsWebApi/Controllers/ShapeController.cs
@@ -1,4 +1,5 @@
 using AipsCore.Application.Abstract;
+using AipsCore.Application.Models.Shape.Command.CreateRectangle;
 using AipsCore.Application.Models.Shape.Command.CreateArrow;
 using AipsCore.Application.Models.Shape.Command.CreateLine;
 using AipsCore.Application.Models.Shape.Command.CreateTextShape;
@@ -11,7 +12,7 @@ namespace AipsWebApi.Controllers;
 public class ShapeController : ControllerBase
 {
     private readonly IDispatcher _dispatcher;
-    
+
     public ShapeController(IDispatcher dispatcher)
     {
         _dispatcher = dispatcher;