Home Programming .NET Core 3.0 Preview 6 is available, packed with updates to compiling...

.NET Core 3.0 Preview 6 is available, packed with updates to compiling assemblies, optimizing applications ASP.NET Core and Blazor

web development
3 min read

Yesterday, the team at Microsoft announced that .NET Core 3.0 Preview 6 is now available. It includes updates for compiling assemblies for improved startup, optimizing applications for size with linker and EventPipe improvements. The team has also released new Docker images for Alpine on ARM64.

Additionally they have made updates to ASP.NET Core and Blazor. The preview comes with new Razor and Blazor directive attributes as well as authentication, authorization support for Blazor apps and much more.

What’s new in the .NET Core 3.0 Preview 6

Docker images

The .NET Core Docker images and repos including microsoft/dotnet and microsoft/dotnet-samples are updated. The Docker images are now available for .NET Core as well as ASP.NET Core on ARM64.

Event Pipe enhancements

With Preview 6, Event Pipe now supports multiple sessions, users can consume events with EventListener in-proc and have out-of-process event pipe clients.

Assembly linking

.NET core 3.0 SDK offers a tool that can help in reducing the size of apps by analyzing IL linker and cutting down on unused assemblies.

Improving the startup time

Users can improve the startup time of their .NET Core application by compiling their application assemblies as ReadyToRun (R2R) format. R2R, a form of ahead-of-time (AOT) compilation is supported with .NET Core 3.0. But it can’t be used with earlier versions of .NET Core.

Additional functionality

The Native Hosting sample posted by the team lately, demonstrates an approach for hosting .NET Core in a native application. The team is now exposing general functionality to .NET Core native hosts as part of .NET Core 3.0.  The functionality is majorly related to assembly loading that makes it easier to produce native hosts.

New Razor features

In this release, the team has added support for the new Razor features which are as follows:


This release comes with new @attribute directive that adds specified attribute to the generated class.


This release comes with new @code directive that is used in .razor files for specifying a code block for adding to the generated class as additional members.


In .razor files, the new @key directive attribute is used for specifying a value that can be used by the Blazor diffing algorithm to preserve elements or components in a list.


The @namespace directive works in pages and views apps and it is also supported with components (.razor).

Blazor directive attributes

In this Blazor release, the team has added standardized common syntax for directive attributes on Blazor which makes the Razor syntax used by Blazor more consistent and predictable.

Event handlers

In Blazor, event handlers now use the new directive attribute syntax than the normal HTML syntax. This new syntax is similar to the HTML syntax, but it has @ character which makes C# event handlers distinct from JS event handlers.

Authentication and authorization support

With this release, Blazor has a built-in support for handling authentication as well as authorization. The server-side Blazor template also supports the options that are used for enabling the standard authentication configurations with ASP.NET Core Identity, Azure AD, and Azure AD B2C.

Certificate and Kerberos authentication to ASP.NET Core

Preview 6 comes along with a Certificate and Kerberos authentication to ASP.NET Core. Certificate authentication requires users to configure the server for accepting certificates, and then add the authentication middleware in Startup.Configure and the certificate authentication service in Startup.ConfigureServices.

Users are happy with this news and they think the updates will be useful.

To know more about this news, check out the official blog post.

Read Next

.NET Core releases May 2019 updates

An introduction to TypeScript types for ASP.NET core [Tutorial]

What to expect in ASP.NET Core 3.0