diff --git a/README.md b/README.md
index 72f4a43..3078d5e 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@ An OpenAPI tool to compare OpenAPI Specifications.
 
 ## C# Library
 
-The tool is available as a [nuget package](https://www.nuget.org/packages/Criteo.OpenApi.Comparator), directly usable into your C# application. 
+The tool is available as a [nuget package](https://www.nuget.org/packages/Criteo.OpenApi.Comparator), directly usable into your C# application.
 
 To install it run the command:
 ```bash
@@ -21,7 +21,7 @@ var differences = OpenApiComparator.Compare(
 
 ## Command line tool
 
-The comparator is also available as a [command line tool](https://www.nuget.org/packages/Criteo.OpenApi.Comparator.Cli/0.1.0). 
+The comparator is also available as a [command line tool](https://www.nuget.org/packages/Criteo.OpenApi.Comparator.Cli/0.1.0).
 
 To install it, run the command:
 ```bash
@@ -34,12 +34,13 @@ openapi-compare -o new_oas.json -n old_oas.json -f Json
 ```
 
 Available options:
-| Option         | Small | Required | Description                                                                                                  |
-|----------------|-------|----------|--------------------------------------------------------------------------------------------------------------|
-| --old          | -o    | true     | Path to old OpenAPI Specification                                                                            |
-| --new          | -n    | true     | Path to new OpenAPI Specification                                                                            |
-| --outputFormat | -f    | false    | Specifies in which format the differences should be displayed (default Json). Possible values: Json \| Text. |
-| --help         | -h    | false    | Log available options                                                                                        |
+| Option         | Small | Required | Description                                                                                                   |
+|----------------|-------|----------|---------------------------------------------------------------------------------------------------------------|
+| --old          | -o    | true     | Path or URL to old OpenAPI Specification.                                                                     |
+| --new          | -n    | true     | Path or URL to new OpenAPI Specification.                                                                     |
+| --outputFormat | -f    | false    | (Default: Json) Specifies in which format the differences should be displayed. Possible values: Json \| Text. |
+| --strict       | -s    | false    | (Default: false) Enable strict mode: breaking changes are errors instead of warnings.                         |
+| --help         | -h    | false    | Log available options                                                                                         |
 
 ## Comparison rules
 
diff --git a/src/Criteo.OpenApi.Comparator.Cli/Options.cs b/src/Criteo.OpenApi.Comparator.Cli/Options.cs
index 1f6feeb..efcfab0 100644
--- a/src/Criteo.OpenApi.Comparator.Cli/Options.cs
+++ b/src/Criteo.OpenApi.Comparator.Cli/Options.cs
@@ -13,20 +13,30 @@ public class Options
         /// <summary>
         /// Path to old OpenAPI Specification
         /// </summary>
-        [Option('o', "old", Required = true, HelpText = "Path or URL to old OpenAPI Specification.")]
+        [Option('o', "old", Required = true,
+            HelpText = "Path or URL to old OpenAPI Specification.")]
         public string OldSpec { get; set; }
 
         /// <summary>
         /// Path to new OpenAPI Specification
         /// </summary>
-        [Option('n', "new", Required = true, HelpText = "Path or URL to new OpenAPI Specification.")]
+        [Option('n', "new", Required = true,
+            HelpText = "Path or URL to new OpenAPI Specification.")]
         public string NewSpec { get; set; }
 
         /// <summary>
         /// Specifies in which format the differences should be displayed (default Json)
         /// </summary>
-        [Option('f', "outputFormat", Required = false, HelpText = "Specifies in which format the differences should be displayed (default Json). Possible values: Json | Text.")]
+        [Option('f', "outputFormat", Required = false, Default = OutputFormat.Json,
+            HelpText = "Specifies in which format the differences should be displayed. Possible values: Json | Text.")]
         public OutputFormat OutputFormat { get; set; } = OutputFormat.Json;
+
+        /// <summary>
+        /// Enable strict mode
+        /// </summary>
+        [Option('s', "strict", Required = false, Default = false,
+            HelpText = "Enable strict mode: breaking changes are errors instead of warnings.")]
+        public bool StrictMode { get; set; } = false;
     }
 
     /// <summary>
@@ -44,4 +54,4 @@ public enum OutputFormat
         /// </summary>
         Text = 1,
     }
-}
\ No newline at end of file
+}
diff --git a/src/Criteo.OpenApi.Comparator.Cli/Program.cs b/src/Criteo.OpenApi.Comparator.Cli/Program.cs
index 1c4b53f..fde605a 100644
--- a/src/Criteo.OpenApi.Comparator.Cli/Program.cs
+++ b/src/Criteo.OpenApi.Comparator.Cli/Program.cs
@@ -38,7 +38,8 @@ public static int Main(string[] args)
                 return 1;
             }
 
-            var differences = OpenApiComparator.Compare(oldOpenApiSpecification, newOpenApiSpecification);
+            var differences = OpenApiComparator.Compare(
+                oldOpenApiSpecification, newOpenApiSpecification, options.StrictMode);
 
             DisplayOutput(differences, options.OutputFormat);
 
diff --git a/src/Criteo.OpenApi.Comparator/OpenApiComparator.cs b/src/Criteo.OpenApi.Comparator/OpenApiComparator.cs
index 8d4c669..1f6e546 100644
--- a/src/Criteo.OpenApi.Comparator/OpenApiComparator.cs
+++ b/src/Criteo.OpenApi.Comparator/OpenApiComparator.cs
@@ -17,12 +17,13 @@ public static class OpenApiComparator
         /// </summary>
         /// <param name="oldOpenApiSpec">The content of the old OpenAPI Specification</param>
         /// <param name="newOpenApiSpec">The content of the new OpenAPI Specification</param>
-        public static IEnumerable<ComparisonMessage> Compare(string oldOpenApiSpec, string newOpenApiSpec)
+        /// <param name="strict">If true, then breaking changes are errors instead of warnings.</param>
+        public static IEnumerable<ComparisonMessage> Compare(string oldOpenApiSpec, string newOpenApiSpec, bool strict = false)
         {
             var oldOpenApiDocument = OpenApiParser.Parse(oldOpenApiSpec);
             var newOpenApiDocument = OpenApiParser.Parse(newOpenApiSpec);
 
-            var context = new ComparisonContext(oldOpenApiDocument, newOpenApiDocument);
+            var context = new ComparisonContext(oldOpenApiDocument, newOpenApiDocument) { Strict = strict };
 
             var comparator = new OpenApiDocumentComparator();
             var comparisonMessages = comparator.Compare(context, oldOpenApiDocument.Typed, newOpenApiDocument.Typed);