diff --git a/src/dotnet/CommandLine/CommandParsingException.cs b/src/dotnet/CommandLine/CommandParsingException.cs
index ef8aaf470..606db5564 100644
--- a/src/dotnet/CommandLine/CommandParsingException.cs
+++ b/src/dotnet/CommandLine/CommandParsingException.cs
@@ -8,18 +8,21 @@ namespace Microsoft.DotNet.Cli.CommandLine
 {
     internal class CommandParsingException : Exception
     {
-        private bool _isRequireSubCommandMissing;
+        private readonly bool _isRequireSubCommandMissing;
+
+        public CommandParsingException(string message) : base(message)
+        {
+            Data.Add("CLI_User_Displayed_Exception", true);
+        }
 
         public CommandParsingException(
             CommandLineApplication command,
             string message,
             bool isRequireSubCommandMissing = false)
-            : base(message)
+            : this(message)
         {
             Command = command;
             _isRequireSubCommandMissing = isRequireSubCommandMissing;
-
-            Data.Add("CLI_User_Displayed_Exception", true);
         }
 
         public CommandLineApplication Command { get; }
@@ -29,9 +32,9 @@ namespace Microsoft.DotNet.Cli.CommandLine
             get
             {
                 return _isRequireSubCommandMissing
-                     ? CommonLocalizableStrings.RequiredCommandNotPassed
-                     : base.Message;
+                           ? CommonLocalizableStrings.RequiredCommandNotPassed
+                           : base.Message;
             }
         }
     }
-}
+}
\ No newline at end of file
diff --git a/src/dotnet/CommonOptions.cs b/src/dotnet/CommonOptions.cs
index 67df7f4e8..277e90211 100644
--- a/src/dotnet/CommonOptions.cs
+++ b/src/dotnet/CommonOptions.cs
@@ -65,6 +65,22 @@ namespace Microsoft.DotNet.Cli
         public static ArgumentsRule DefaultToCurrentDirectory(this ArgumentsRule rule) =>
             rule.With(defaultValue: () => PathUtility.EnsureTrailingSlash(Directory.GetCurrentDirectory()));
 
+        public static ArgumentsRule ExistingFilesOnly(
+            this ArgumentsRule rule) =>
+            rule.And(new ArgumentsRule(o =>
+            {
+                foreach (var filePath in o.Arguments)
+                {
+                    if (!File.Exists(filePath) &&
+                        !Directory.Exists(filePath))
+                    {
+                        return $"File not found: {filePath}";
+                    }
+                }
+
+                return null;
+            }));
+
         public static ArgumentsRule ExistingSlnFileOrDirectoryOnly(
             this ArgumentsRule rule) =>
             rule
diff --git a/src/dotnet/DotNetTopLevelCommandBase.cs b/src/dotnet/DotNetTopLevelCommandBase.cs
index f1469da2b..17cdb5e30 100644
--- a/src/dotnet/DotNetTopLevelCommandBase.cs
+++ b/src/dotnet/DotNetTopLevelCommandBase.cs
@@ -25,7 +25,7 @@ namespace Microsoft.DotNet.Cli
 
             var result = parser.ParseFrom($"dotnet {CommandName}", args);
 
-            result.ShowHelpIfRequested();
+            result.ShowHelpOrErrorIfAppropriate();
 
             var subcommandName = result.Command().Name;
 
diff --git a/src/dotnet/ParseResultExtensions.cs b/src/dotnet/ParseResultExtensions.cs
index f19d0cd94..d98991fa4 100644
--- a/src/dotnet/ParseResultExtensions.cs
+++ b/src/dotnet/ParseResultExtensions.cs
@@ -12,8 +12,15 @@ namespace Microsoft.DotNet.Cli
         public static void ShowHelp(this ParseResult parseResult) =>
             Console.WriteLine(parseResult.Command().HelpView());
 
-        public static void ShowHelpIfRequested(this ParseResult parseResult)
+        public static void ShowHelpOrErrorIfAppropriate(this ParseResult parseResult)
         {
+            if (parseResult.Errors.Any())
+            {
+                throw new CommandParsingException(
+                    string.Join(Environment.NewLine,
+                                parseResult.Errors.Select(e => e.Message)));
+            }
+
             if (parseResult.AppliedCommand().HasOption("help"))
             {
                 // NOTE: this is a temporary stage in refactoring toward the ClicCommandLineParser being used at the CLI entry point. 
diff --git a/src/dotnet/commands/dotnet-add/AddCommandParser.cs b/src/dotnet/commands/dotnet-add/AddCommandParser.cs
index 062a97a11..dcc48737a 100644
--- a/src/dotnet/commands/dotnet-add/AddCommandParser.cs
+++ b/src/dotnet/commands/dotnet-add/AddCommandParser.cs
@@ -8,6 +8,7 @@ using System.Net.Http;
 using System.Threading;
 using Microsoft.DotNet.Cli.CommandLine;
 using Newtonsoft.Json.Linq;
+using LocalizableStrings = Microsoft.DotNet.Tools.Add.PackageReference.LocalizableStrings;
 
 namespace Microsoft.DotNet.Cli
 {
@@ -23,7 +24,7 @@ namespace Microsoft.DotNet.Cli
                 Create.Command(
                     "package",
                     ".NET Add Package reference Command",
-                    Accept.ExactlyOneArgument()
+                    Accept.ExactlyOneArgument(errorMessage: o => LocalizableStrings.SpecifyExactlyOnePackageReference)
                           .WithSuggestionsFrom(QueryNuGet),
                     CommonOptions.HelpOption(),
                     Create.Option("-v|--version",
diff --git a/src/dotnet/commands/dotnet-build/BuildCommand.cs b/src/dotnet/commands/dotnet-build/BuildCommand.cs
index aef57ebb4..691d5ef21 100644
--- a/src/dotnet/commands/dotnet-build/BuildCommand.cs
+++ b/src/dotnet/commands/dotnet-build/BuildCommand.cs
@@ -25,7 +25,7 @@ namespace Microsoft.DotNet.Tools.Build
 
             var result = parser.ParseFrom("dotnet build", args);
 
-            result.ShowHelpIfRequested();
+            result.ShowHelpOrErrorIfAppropriate();
 
             var appliedBuildOptions = result["dotnet"]["build"];
 
diff --git a/src/dotnet/commands/dotnet-cache/Program.cs b/src/dotnet/commands/dotnet-cache/Program.cs
index 3eb78e3da..64d70a169 100644
--- a/src/dotnet/commands/dotnet-cache/Program.cs
+++ b/src/dotnet/commands/dotnet-cache/Program.cs
@@ -29,7 +29,7 @@ namespace Microsoft.DotNet.Tools.Cache
 
             var result = parser.ParseFrom("dotnet cache", args);
 
-            result.ShowHelpIfRequested();
+            result.ShowHelpOrErrorIfAppropriate();
 
             var appliedBuildOptions = result["dotnet"]["cache"];
 
diff --git a/src/dotnet/commands/dotnet-clean/Program.cs b/src/dotnet/commands/dotnet-clean/Program.cs
index bcedf9501..e07ec356d 100644
--- a/src/dotnet/commands/dotnet-clean/Program.cs
+++ b/src/dotnet/commands/dotnet-clean/Program.cs
@@ -25,7 +25,7 @@ namespace Microsoft.DotNet.Tools.Clean
 
             var result = parser.ParseFrom("dotnet clean", args);
 
-            result.ShowHelpIfRequested();
+            result.ShowHelpOrErrorIfAppropriate();
 
             var parsedClean = result["dotnet"]["clean"];
 
diff --git a/src/dotnet/commands/dotnet-migrate/Program.cs b/src/dotnet/commands/dotnet-migrate/Program.cs
index ce406290c..72001edd7 100644
--- a/src/dotnet/commands/dotnet-migrate/Program.cs
+++ b/src/dotnet/commands/dotnet-migrate/Program.cs
@@ -20,7 +20,7 @@ namespace Microsoft.DotNet.Tools.Migrate
 
             var result = parser.ParseFrom("dotnet migrate", args);
 
-            result.ShowHelpIfRequested();
+            result.ShowHelpOrErrorIfAppropriate();
 
             return result["dotnet"]["migrate"].Value<MigrateCommand>();
         }
diff --git a/src/dotnet/commands/dotnet-pack/PackCommand.cs b/src/dotnet/commands/dotnet-pack/PackCommand.cs
index 37f4dbe61..2821c23d8 100644
--- a/src/dotnet/commands/dotnet-pack/PackCommand.cs
+++ b/src/dotnet/commands/dotnet-pack/PackCommand.cs
@@ -24,7 +24,7 @@ namespace Microsoft.DotNet.Tools.Pack
 
             var result = parser.ParseFrom("dotnet pack", args);
 
-            result.ShowHelpIfRequested();
+            result.ShowHelpOrErrorIfAppropriate();
 
             var parsedPack = result["dotnet"]["pack"];
           
diff --git a/src/dotnet/commands/dotnet-publish/Program.cs b/src/dotnet/commands/dotnet-publish/Program.cs
index 8a556f5fa..8c8fbc9cf 100644
--- a/src/dotnet/commands/dotnet-publish/Program.cs
+++ b/src/dotnet/commands/dotnet-publish/Program.cs
@@ -27,7 +27,7 @@ namespace Microsoft.DotNet.Tools.Publish
 
             var result = parser.ParseFrom("dotnet publish", args);
 
-            result.ShowHelpIfRequested();
+            result.ShowHelpOrErrorIfAppropriate();
 
             msbuildArgs.Add("/t:Publish");
 
diff --git a/src/dotnet/commands/dotnet-restore/Program.cs b/src/dotnet/commands/dotnet-restore/Program.cs
index 01b456109..1e1ff728d 100644
--- a/src/dotnet/commands/dotnet-restore/Program.cs
+++ b/src/dotnet/commands/dotnet-restore/Program.cs
@@ -29,7 +29,7 @@ namespace Microsoft.DotNet.Tools.Restore
 
             var result = parser.ParseFrom("dotnet restore", args);
 
-            result.ShowHelpIfRequested();
+            result.ShowHelpOrErrorIfAppropriate();
 
             var parsedRestore = result["dotnet"]["restore"];
 
diff --git a/src/dotnet/commands/dotnet-run/Program.cs b/src/dotnet/commands/dotnet-run/Program.cs
index 016aa5422..6bfaffefa 100644
--- a/src/dotnet/commands/dotnet-run/Program.cs
+++ b/src/dotnet/commands/dotnet-run/Program.cs
@@ -17,7 +17,7 @@ namespace Microsoft.DotNet.Tools.Run
 
             var result = parser.ParseFrom("dotnet run", args);
 
-            result.ShowHelpIfRequested();
+            result.ShowHelpOrErrorIfAppropriate();
 
             return result["dotnet"]["run"].Value<RunCommand>();
         }
diff --git a/src/dotnet/commands/dotnet-sln/SlnCommandParser.cs b/src/dotnet/commands/dotnet-sln/SlnCommandParser.cs
index 684809e3e..d20cef621 100644
--- a/src/dotnet/commands/dotnet-sln/SlnCommandParser.cs
+++ b/src/dotnet/commands/dotnet-sln/SlnCommandParser.cs
@@ -13,7 +13,8 @@ namespace Microsoft.DotNet.Cli
                 ".NET modify solution file command",
                 Accept.ExactlyOneArgument()
                       .ExistingSlnFileOrDirectoryOnly()
-                      .DefaultToCurrentDirectory(),
+                      .DefaultToCurrentDirectory()
+                      .With(name: "SLN_FILE" ),
                 CommonOptions.HelpOption(),
                 Create.Command("add",
                                ".NET Add project(s) to a solution file Command",
@@ -21,7 +22,6 @@ namespace Microsoft.DotNet.Cli
                                CommonOptions.HelpOption()),
                 Create.Command("list",
                                "List all projects in the solution.",
-                               Accept.OneOrMoreArguments(),
                                CommonOptions.HelpOption()),
                 Create.Command("remove",
                                "Remove the specified project(s) from the solution. The project is not impacted.",
diff --git a/src/dotnet/commands/dotnet-test/Program.cs b/src/dotnet/commands/dotnet-test/Program.cs
index 563b86be3..913181a20 100644
--- a/src/dotnet/commands/dotnet-test/Program.cs
+++ b/src/dotnet/commands/dotnet-test/Program.cs
@@ -34,7 +34,7 @@ namespace Microsoft.DotNet.Tools.Test
 
             var result = parser.ParseFrom("dotnet test", args);
 
-            result.ShowHelpIfRequested();
+            result.ShowHelpOrErrorIfAppropriate();
 
             var parsedTest = result["dotnet"]["test"];