Blazor WASM in .NET 10 has Faster Startup

With .NET 10, Microsoft went back to the drawing board on how Blazor WASM starts up and ships assets. Instead of making minor, pathed fixes to Blazor WASM, they reworked compression, caching, and bootstrapping. The results are smaller downloads, faster first loads, and a developer experience that finally competes with the mature front-end frameworks.

Here’s what actually changed.

Lighter Payloads with Built-In Compression

The eye-catching number is the reduction of blazor.web.js from 183 KB to just 43 KB (a 76% drop). That comes from Brotli compression being applied during the build process, so you don’t have to configure anything manually.

It’s not just the JavaScript, though. Core assemblies like mscorlib.dll are compressed down by about 50-70%, and even the runtime itself is approximately a megabyte lighter.

Just as important, these assets are now fingerprinted automatically. That means no more “clear cache and try again” messages after a deploy. Every update gets a new hash in the filename, and the browser always pulls the latest copy.

A single property in your .csproj enables cache-busting placeholders in your index.html:

<PropertyGroup>
  <OverrideHtmlAssetPlaceholders>true</OverrideHtmlAssetPlaceholders>
</PropertyGroup>

Parallel Preloading Files

Previously, Blazor apps had a strict loading order: HTML → JavaScript → runtime → DLLs → app. Each step waited for the previous one to finish, creating a synchronous bottleneck that wasted precious seconds.

.NET 10 fixes this with the new <ResourcePreloader /> Razor component. It emits <link rel="preload"> tags for the runtime and assemblies so that they start downloading right away. By the time the JavaScript loader runs, the other files are already downloading.

This small change significantly reduces the time before the app loads completely.

Streamlined Bootstrapping

Older Blazor WASM versions required blazor.boot.json to describe which files to load. That extra fetch may have seemed minor, but it was still a blocking call before the app could even begin.

In .NET 10, that manifest is gone. Its data is part of dotnet.js, which is fingerprinted and cached. Fewer round trips and a faster startup.

Playing Well with JavaScript Build Systems

In another notable shift, Blazor WASM can now integrate directly into existing JavaScript pipelines. If you enable the following in your project file, the output becomes friendly to bundlers like Vite and webpack.

<PropertyGroup>
  <WasmBundlerFriendlyBootConfig>true</WasmBundlerFriendlyBootConfig>
</PropertyGroup>

Now you are able to treat Blazor as just another piece of a front-end stack. Want a Blazor data grid inside a Vue dashboard? Or C# logic powering part of a React app? That’s now possible without rewriting your build scripts from scratch.

Serious Diagnostics in the Browser

Performance tuning used to be hit and miss. With .NET 10, you can capture runtime traces directly from the browser.

Create a .nettrace file from your Blazor WASM app that you can open in Visual Studio. You get the same profiling tools you’d use for a backend service but applied to WebAssembly.

That means you can accurately measure your app performance and act on the data.

For years, Blazor WASM has had a reputation for sluggish load times. With .NET 10, Microsoft has closed much of the gap. Compression and fingerprinting shrink the payload, parallel preloading accelerates startup, and better tooling helps you fine-tune performance. Now is the time to build those snappy Blazor WASM applications!