diff --git a/LocalisationAnalyser/Analysers/LocalisationKeyUsedMultipleTimesInClassAnalyser.cs b/LocalisationAnalyser/Analysers/LocalisationKeyUsedMultipleTimesInClassAnalyser.cs
index 560bcd6..d8bc871 100644
--- a/LocalisationAnalyser/Analysers/LocalisationKeyUsedMultipleTimesInClassAnalyser.cs
+++ b/LocalisationAnalyser/Analysers/LocalisationKeyUsedMultipleTimesInClassAnalyser.cs
@@ -1,13 +1,118 @@
+using System.Collections.Generic;
 using System.Collections.Immutable;
+using System.Linq;
+using LocalisationAnalyser.Localisation;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Diagnostics;
 
 namespace LocalisationAnalyser.Analysers
 {
     [DiagnosticAnalyzer(LanguageNames.CSharp)]
-    public class LocalisationKeyUsedMultipleTimesInClassAnalyser : AbstractMemberAnalyser
+    public class LocalisationKeyUsedMultipleTimesInClassAnalyser : DiagnosticAnalyzer
     {
         public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics =>
             ImmutableArray.Create(DiagnosticRules.LOCALISATION_KEY_USED_MULTIPLE_TIMES_IN_CLASS);
+
+        public override void Initialize(AnalysisContext context)
+        {
+            // See https://github.com/dotnet/roslyn/blob/main/docs/analyzers/Analyzer%20Actions%20Semantics.md for more information
+            context.ConfigureGeneratedCodeAnalysis(GeneratedCodeAnalysisFlags.None);
+            context.EnableConcurrentExecution();
+
+            context.RegisterSyntaxTreeAction(analyseSyntaxTree);
+        }
+
+        private void analyseSyntaxTree(SyntaxTreeAnalysisContext context)
+        {
+            // Optimisation to not inspect too many files.
+            if (!context.Tree.FilePath.EndsWith("Strings.cs"))
+                return;
+
+            if (!LocalisationFile.TryRead(context.Tree, out var file, out _))
+                return;
+
+            var duplicateKeys = findDuplicateKeys(file).ToImmutableHashSet();
+
+            var root = context.Tree.GetRoot();
+
+            foreach (var property in root.DescendantNodes().OfType<PropertyDeclarationSyntax>())
+                markPropertyIfDuplicate(context, property, file, duplicateKeys);
+
+            foreach (var method in root.DescendantNodes().OfType<MethodDeclarationSyntax>())
+                markMethodIfDuplicate(context, method, file, duplicateKeys);
+        }
+
+        private IEnumerable<string> findDuplicateKeys(LocalisationFile localisationFile)
+        {
+            var hashSet = new HashSet<string>();
+
+            foreach (var member in localisationFile.Members)
+            {
+                if (!hashSet.Add(member.Key))
+                    yield return member.Key;
+            }
+        }
+
+        private void markMethodIfDuplicate(SyntaxTreeAnalysisContext context, MethodDeclarationSyntax method,
+            LocalisationFile localisationFile, ImmutableHashSet<string> duplicateKeys)
+        {
+            string? name = method.Identifier.Text;
+            if (name == null)
+                return;
+
+            var member = localisationFile.Members.SingleOrDefault(m =>
+                m.Name == name && m.Parameters.Length == method.ParameterList.Parameters.Count);
+
+            if (member == null)
+                return;
+
+            if (!duplicateKeys.Contains(member.Key))
+                return;
+
+            var creationExpression = (ObjectCreationExpressionSyntax)method.ExpressionBody.Expression;
+            var keyArgument = creationExpression.ArgumentList!.Arguments[0];
+
+            if (keyArgument.Expression is not InvocationExpressionSyntax methodInvocation
+                || (methodInvocation.Expression as IdentifierNameSyntax)?.Identifier.Text != "getKey"
+                || methodInvocation.ArgumentList.Arguments.Count != 1)
+            {
+                return;
+            }
+
+            var keyString = methodInvocation.ArgumentList.Arguments[0];
+
+            context.ReportDiagnostic(Diagnostic.Create(DiagnosticRules.LOCALISATION_KEY_USED_MULTIPLE_TIMES_IN_CLASS, keyString.GetLocation(), member.Key));
+        }
+
+        private void markPropertyIfDuplicate(SyntaxTreeAnalysisContext context, PropertyDeclarationSyntax property,
+            LocalisationFile localisationFile, ImmutableHashSet<string> duplicateKeys)
+        {
+            string? name = property.Identifier.Text;
+            if (name == null)
+                return;
+
+            var member = localisationFile.Members.SingleOrDefault(m => m.Name == name && m.Parameters.Length == 0);
+
+            if (member == null)
+                return;
+
+            if (!duplicateKeys.Contains(member.Key))
+                return;
+
+            var creationExpression = (ObjectCreationExpressionSyntax)property.ExpressionBody.Expression;
+            var keyArgument = creationExpression.ArgumentList!.Arguments[0];
+
+            if (keyArgument.Expression is not InvocationExpressionSyntax methodInvocation
+                || (methodInvocation.Expression as IdentifierNameSyntax)?.Identifier.Text != "getKey"
+                || methodInvocation.ArgumentList.Arguments.Count != 1)
+            {
+                return;
+            }
+
+            var keyString = methodInvocation.ArgumentList.Arguments[0];
+
+            context.ReportDiagnostic(Diagnostic.Create(DiagnosticRules.LOCALISATION_KEY_USED_MULTIPLE_TIMES_IN_CLASS, keyString.GetLocation(), member.Key));
+        }
     }
 }
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