diff --git a/src/Microsoft.OpenApi.Hidi/OpenApiService.cs b/src/Microsoft.OpenApi.Hidi/OpenApiService.cs
index 8cf5bb60e..abef3617f 100644
--- a/src/Microsoft.OpenApi.Hidi/OpenApiService.cs
+++ b/src/Microsoft.OpenApi.Hidi/OpenApiService.cs
@@ -23,8 +23,8 @@ public static class OpenApiService
         public static void ProcessOpenApiDocument(
             string input,
             FileInfo output,
-            OpenApiSpecVersion version,
-            OpenApiFormat format,
+            OpenApiSpecVersion? version,
+            OpenApiFormat? format,
             string filterByOperationIds,
             string filterByTags,
             string filterByCollection,
@@ -101,13 +101,16 @@ public static void ProcessOpenApiDocument(
             {
                 ReferenceInline = inline ? ReferenceInlineSetting.InlineLocalReferences : ReferenceInlineSetting.DoNotInlineReferences
             };
-            IOpenApiWriter writer = format switch
+
+            var openApiFormat = format ?? GetOpenApiFormat(input);
+            var openApiVersion = version ?? result.OpenApiDiagnostic.SpecificationVersion;
+            IOpenApiWriter writer = openApiFormat switch
             {
                 OpenApiFormat.Json => new OpenApiJsonWriter(textWriter, settings),
                 OpenApiFormat.Yaml => new OpenApiYamlWriter(textWriter, settings),
                 _ => throw new ArgumentException("Unknown format"),
             };
-            document.Serialize(writer, version);
+            document.Serialize(writer, openApiVersion);
 
             textWriter.Flush();
         }
@@ -198,5 +201,10 @@ internal static void ValidateOpenApiDocument(string input)
 
             Console.WriteLine(statsVisitor.GetStatisticsReport());
         }
+
+        private static OpenApiFormat GetOpenApiFormat(string input)
+        {
+            return !input.StartsWith("http") && Path.GetExtension(input) == ".json" ? OpenApiFormat.Json : OpenApiFormat.Yaml;
+        }
     }
 }
diff --git a/src/Microsoft.OpenApi.Hidi/Program.cs b/src/Microsoft.OpenApi.Hidi/Program.cs
index 099eb70df..b3752ef97 100644
--- a/src/Microsoft.OpenApi.Hidi/Program.cs
+++ b/src/Microsoft.OpenApi.Hidi/Program.cs
@@ -33,7 +33,7 @@ static async Task<int> Main(string[] args)
                 new Option("--filterByTags", "Filters OpenApiDocument by Tag(s) provided", typeof(string)),
                 new Option("--filterByCollection", "Filters OpenApiDocument by Postman collection provided", typeof(string))
             };
-            transformCommand.Handler = CommandHandler.Create<string, FileInfo, OpenApiSpecVersion, OpenApiFormat, string, string, string, bool, bool>(
+            transformCommand.Handler = CommandHandler.Create<string, FileInfo, OpenApiSpecVersion?, OpenApiFormat?, string, string, string, bool, bool>(
                 OpenApiService.ProcessOpenApiDocument);
 
             rootCommand.Add(transformCommand);
diff --git a/test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt b/test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt
index cb2a133cf..f700fee15 100755
--- a/test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt
+++ b/test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt
@@ -959,7 +959,6 @@ namespace Microsoft.OpenApi.Services
         public static Microsoft.OpenApi.Models.OpenApiDocument CreateFilteredDocument(Microsoft.OpenApi.Models.OpenApiDocument source, System.Func<string, Microsoft.OpenApi.Models.OperationType?, Microsoft.OpenApi.Models.OpenApiOperation, bool> predicate) { }
         public static Microsoft.OpenApi.Services.OpenApiUrlTreeNode CreateOpenApiUrlTreeNode(System.Collections.Generic.Dictionary<string, Microsoft.OpenApi.Models.OpenApiDocument> sources) { }
         public static System.Func<string, Microsoft.OpenApi.Models.OperationType?, Microsoft.OpenApi.Models.OpenApiOperation, bool> CreatePredicate(string operationIds = null, string tags = null, System.Collections.Generic.Dictionary<string, System.Collections.Generic.List<string>> requestUrls = null, Microsoft.OpenApi.Models.OpenApiDocument source = null) { }
-        public static System.Collections.Generic.Dictionary<string, System.Collections.Generic.List<string>> ParseJsonCollectionFile(System.IO.Stream stream) { }
     }
     public class OpenApiReferenceError : Microsoft.OpenApi.Models.OpenApiError
     {