diff --git a/StepLang/Framework/Pure/ContainsKeyFunction.cs b/StepLang/Framework/Pure/ContainsKeyFunction.cs
new file mode 100644
index 00000000..b1dd3343
--- /dev/null
+++ b/StepLang/Framework/Pure/ContainsKeyFunction.cs
@@ -0,0 +1,22 @@
+using StepLang.Expressions.Results;
+using StepLang.Interpreting;
+using StepLang.Tokenizing;
+
+namespace StepLang.Framework.Pure;
+
+public class ContainsKeyFunction : GenericFunction<MapResult, StringResult>
+{
+    public const string Identifier = "containsKey";
+
+    protected override IEnumerable<NativeParameter> NativeParameters { get; } = new NativeParameter[] {
+        new(OnlyMap, "subject"),
+        new(OnlyString, "key"),
+    };
+
+    protected override IEnumerable<ResultType> ReturnTypes { get; } = OnlyBool;
+
+    protected override BoolResult Invoke(TokenLocation callLocation, Interpreter interpreter, MapResult argument1, StringResult argument2)
+    {
+        return argument1.Value.ContainsKey(argument2.Value);
+    }
+}
diff --git a/StepLang/Interpreting/Scope.cs b/StepLang/Interpreting/Scope.cs
index b67f2981..7c18d249 100644
--- a/StepLang/Interpreting/Scope.cs
+++ b/StepLang/Interpreting/Scope.cs
@@ -39,6 +39,7 @@ private Scope()
         CreateVariable(SubstringFunction.Identifier, new SubstringFunction().ToResult());
         CreateVariable(IndexOfFunction.Identifier, new IndexOfFunction().ToResult());
         CreateVariable(ContainsFunction.Identifier, new ContainsFunction().ToResult());
+        CreateVariable(ContainsKeyFunction.Identifier, new ContainsKeyFunction().ToResult());
         CreateVariable(StartsWithFunction.Identifier, new StartsWithFunction().ToResult());
         CreateVariable(EndsWithFunction.Identifier, new EndsWithFunction().ToResult());
         CreateVariable(PrintFunction.Identifier, new PrintFunction().ToResult());