Migrating from WebForms to WebForms Core: A Modern Developer’s Guide

Yes, you read that right — WebForms Core. It’s not an official Microsoft product, but many of us who’ve lived through the glorious (and painful) days of ASP.NET WebForms are either still maintaining legacy apps or looking for a path to modernize — without rewriting everything from scratch.

Let’s talk about what it really takes to migrate from classic WebForms to a modern architecture while retaining some of the component-based benefits WebForms provided.

Why Migrate from WebForms?

• End of the road: WebForms is not supported in .NET Core/.NET 5+.
• Performance bottlenecks: ViewState and postbacks can slow things down.
• Poor testability: Tightly coupled code and limited separation of concerns.
• Modern DevOps is hard: WebForms doesn’t play well with CI/CD, containers, or cross-platform dev.

What is "WebForms Core"?

There is no official WebForms Core. However, developers often refer to modern ASP.NET Core architectures that emulate WebForms patterns (page lifecycle, code-behind separation, event-driven model) using:

• Razor Pages or Blazor
• Component-based design
• Dependency Injection
• Routing & Middleware in ASP.NET Core

Step-by-Step Migration Strategy

1. Audit and Modularize Your Current WebForms App

Identify:

• Number of .aspx pages and controls
• Business logic in code-behind files
• Master Pages, custom controls, ViewState usage

Refactor:

• Move business logic to separate classes/services
• Separate UI and logic for easier mapping

2. Choose Your Migration Target

Tip: If you're moving from event-driven UI logic, Blazor Server might feel the most "familiar."

3. Rebuild UI with Razor or Blazor

Start small:

• Pick one or two pages
• Recreate them in Razor Pages or Blazor
• Match old ViewModel with new structure

Convert controls to:

• HTML + TagHelpers (for Razor)
• Blazor Components (for Blazor)

Say goodbye to ViewState — use proper state management in Blazor (e.g., cascading values, local state) or pass models in Razor Pages.

4. Rewire Your Code-Behind Logic

Instead of:

protected void btnSubmit_Click(object sender, EventArgs e)
{
    DoSomething();
}

You’ll use:

Razor Pages:

public async Task<IActionResult> OnPostAsync()
{
    await DoSomething();
    return Page();
}

Blazor:

<button @onclick="DoSomething">Submit</button>

@code {
    private void DoSomething() { ... }
}

5. Integrate Business Logic and Services

Migrate your business logic into dependency-injected services:

services.AddScoped<IOrderService, OrderService>();

This is where your SOLID principles will finally get the room they deserve!

6. Test & Deploy Incrementally

Start with hybrid hosting (host ASP.NET Core app inside IIS alongside legacy app)

• Rewrite module by module
• Use reverse proxy or URL rewriting to forward traffic
• Eventually decommission old parts as you migrate

Bonus Tips

• Avoid 1-to-1 porting — rethink UX and architecture
• Invest in automated testing for new components
• Implement modern security practices (e.g., ASP.NET Core Identity, OAuth)
• Use feature flags to toggle between old/new pages

Conclusion

Migrating from WebForms to a modern .NET Core platform is challenging, but it doesn’t have to be a rewrite from scratch. Tools like Razor Pages and Blazor offer familiar paradigms with modern performance, testability, and scalability.

Your legacy app deserves a second life. Start small, refactor smartly, and keep shipping.

Let’s Talk!

Have you migrated a WebForms app recently? Did you go Razor, MVC, or full Blazor? Share your journey, struggles, and wins in the comments!