What Is Blazor? Building Web UIs with .NET and WebAssembly

Blazor is a cutting-edge framework from Microsoft that allows developers to build interactive web applications using C# and .NET, running in the browser via WebAssembly. This means you can write rich, client-side web apps without JavaScript.

In this article, we’ll cover what Blazor is, how it works, setup steps, and explore real-world examples and best practices.

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What Is Blazor?

Blazor is part of the ASP.NET Core ecosystem and provides two hosting models:

✅ Blazor WebAssembly (WASM) — Runs C# directly in the browser using WebAssembly.
✅ Blazor Server — Executes C# code on the server, with UI updates sent over a SignalR connection.

The key idea is: you can use C#, Razor, and .NET libraries to build full web UIs, reusing logic across server and client.

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Why Use Blazor?

✅ Full-stack .NET development — share code between frontend and backend.
✅ Avoid JavaScript for most UI logic.
✅ Strong typing, tooling, and compile-time checks.
✅ Access to existing .NET libraries and ecosystem.
✅ Deploy as static files (Blazor WebAssembly) or connected apps (Blazor Server).

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Setting Up Blazor

Step 1: Install SDK

Make sure you have .NET 7 or later installed.

dotnet --version

Step 2: Create a New Blazor WebAssembly App

dotnet new blazorwasm -o BlazorApp
cd BlazorApp

Step 3: Run the App

dotnet run

Visit https://localhost:5001 — you’ll see a running Blazor app!

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Understanding Blazor Components

A Blazor component is a reusable piece of UI, written in .razor files.

Example Counter.razor:

<h3>Counter</h3>

<p>Current count: @currentCount</p>

<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>

@code {
    private int currentCount = 0;

    private void IncrementCount()
    {
        currentCount++;
    }
}

This component updates interactively when the button is clicked.

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Blazor WebAssembly vs Blazor Server

Feature	Blazor WebAssembly	Blazor Server
Runs in	Browser (client-side, WebAssembly)	Server (with SignalR connection)
Performance	Faster for local interactions	Lower initial download, higher latency
Offline support	Yes	No
Resource usage	Uses client resources	Uses server resources

Choose based on your app’s needs.

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Data Binding and Events

Blazor makes binding data simple:

<input @bind="username" />
<p>You typed: @username</p>

@code {
    private string username = "";
}

Events like button clicks:

<button @onclick="HandleClick">Click me</button>

@code {
    void HandleClick()
    {
        Console.WriteLine("Button clicked");
    }
}

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Calling APIs

You can use HttpClient to make API calls:

@inject HttpClient Http

@code {
    WeatherForecast[] forecasts;

    protected override async Task OnInitializedAsync()
    {
        forecasts = await Http.GetFromJsonAsync<WeatherForecast[]>("WeatherForecast");
    }
}

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Best Practices

✅ Use components to break UI into reusable pieces.
✅ Avoid large monolithic pages — keep things modular.
✅ Use asynchronous methods (async/await) for I/O work.
✅ Consider Blazor WebAssembly size optimization (AOT, trimming) for production.
✅ Protect server-side resources with authentication and authorization.

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Real-World Use Cases

• Internal business apps (dashboards, forms, management tools)
• Progressive Web Apps (PWAs) with offline support
• Interactive public websites with live data
• Hybrid apps (with .NET MAUI or Electron)

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Summary

Blazor represents a major leap forward in .NET web development, allowing you to write client-side, interactive web UIs using C# and WebAssembly. Whether you choose Blazor WebAssembly or Blazor Server, the framework empowers you to create rich, maintainable web apps using the full .NET ecosystem.