diff --git a/Checksums/Checksums.sln b/Checksums/Checksums.sln
index 35c158b..8fc3432 100644
--- a/Checksums/Checksums.sln
+++ b/Checksums/Checksums.sln
@@ -3,7 +3,16 @@ Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 17
 VisualStudioVersion = 17.2.32516.85
 MinimumVisualStudioVersion = 10.0.40219.1
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "ISBN", "ISBN\ISBN.csproj", "{3BFA78C7-4DE1-46CD-912F-59D3DE0B9788}"
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "ISBN", "ISBN\ISBN.csproj", "{3BFA78C7-4DE1-46CD-912F-59D3DE0B9788}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "EANValidator", "EANValidator\EANValidator.csproj", "{2E12BD9A-5E23-4ED9-8B1C-63C8AB19D39D}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "dotFionn.Checksum.Utils", "dotFionn.Checksum.Utils\dotFionn.Checksum.Utils.csproj", "{B8ED20C2-C851-47B8-8509-12E4A3D2F18C}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "test", "test\test.csproj", "{DAE25550-52A1-440A-B6B9-C588357620D4}"
+	ProjectSection(ProjectDependencies) = postProject
+		{B8ED20C2-C851-47B8-8509-12E4A3D2F18C} = {B8ED20C2-C851-47B8-8509-12E4A3D2F18C}
+	EndProjectSection
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -15,6 +24,18 @@ Global
 		{3BFA78C7-4DE1-46CD-912F-59D3DE0B9788}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{3BFA78C7-4DE1-46CD-912F-59D3DE0B9788}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{3BFA78C7-4DE1-46CD-912F-59D3DE0B9788}.Release|Any CPU.Build.0 = Release|Any CPU
+		{2E12BD9A-5E23-4ED9-8B1C-63C8AB19D39D}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{2E12BD9A-5E23-4ED9-8B1C-63C8AB19D39D}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{2E12BD9A-5E23-4ED9-8B1C-63C8AB19D39D}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{2E12BD9A-5E23-4ED9-8B1C-63C8AB19D39D}.Release|Any CPU.Build.0 = Release|Any CPU
+		{B8ED20C2-C851-47B8-8509-12E4A3D2F18C}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{B8ED20C2-C851-47B8-8509-12E4A3D2F18C}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{B8ED20C2-C851-47B8-8509-12E4A3D2F18C}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{B8ED20C2-C851-47B8-8509-12E4A3D2F18C}.Release|Any CPU.Build.0 = Release|Any CPU
+		{DAE25550-52A1-440A-B6B9-C588357620D4}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{DAE25550-52A1-440A-B6B9-C588357620D4}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{DAE25550-52A1-440A-B6B9-C588357620D4}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{DAE25550-52A1-440A-B6B9-C588357620D4}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
diff --git a/Checksums/dotFionn.Checksum.Utils/Extensions.cs b/Checksums/dotFionn.Checksum.Utils/Extensions.cs
new file mode 100644
index 0000000..ca622bf
--- /dev/null
+++ b/Checksums/dotFionn.Checksum.Utils/Extensions.cs
@@ -0,0 +1,19 @@
+using System;
+
+namespace dotFionn.Checksum.Utils
+{
+    public static class Extensions
+    {
+        public static int digitSum(this int inInt)
+        {
+            int digitSum = 0;
+
+            while (inInt > 0) {
+                digitSum += inInt % 10;
+                inInt /= 10;
+            }
+
+            return digitSum;
+        }
+    }
+}
diff --git a/Checksums/dotFionn.Checksum.Utils/dotFionn.Checksum.Utils.csproj b/Checksums/dotFionn.Checksum.Utils/dotFionn.Checksum.Utils.csproj
new file mode 100644
index 0000000..f208d30
--- /dev/null
+++ b/Checksums/dotFionn.Checksum.Utils/dotFionn.Checksum.Utils.csproj
@@ -0,0 +1,7 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net5.0</TargetFramework>
+  </PropertyGroup>
+
+</Project>
diff --git a/Checksums/test/Program.cs b/Checksums/test/Program.cs
new file mode 100644
index 0000000..6cf112a
--- /dev/null
+++ b/Checksums/test/Program.cs
@@ -0,0 +1,15 @@
+using System;
+using dotFionn.Checksum.Utils;
+
+namespace test
+{
+    internal class Program
+    {
+        static void Main(string[] args)
+        {
+            Console.WriteLine("Hello World!");
+            Console.WriteLine(123.digitSum());
+            
+        }
+    }
+}
diff --git a/Checksums/test/test.csproj b/Checksums/test/test.csproj
new file mode 100644
index 0000000..18e5926
--- /dev/null
+++ b/Checksums/test/test.csproj
@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net5.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\dotFionn.Checksum.Utils\dotFionn.Checksum.Utils.csproj" />
+  </ItemGroup>
+
+</Project>