Blazor static SSR gets [SupplyParameterFromSession] in .NET 11 Preview 5

.NET 11 Preview 5, which shipped on 2026-06-09, rounds out the family of “supply parameter from X” attributes that Blazor static server-side rendering (static SSR) already had for query strings and form data. The new one is [SupplyParameterFromSession], and it binds a component property to a key in ASP.NET Core’s server session. If you have ever carried a multi-step wizard’s state across static SSR page loads, you know why this matters.

Why session was the awkward one

Static SSR renders plain HTML with no SignalR circuit and no WebAssembly payload, so there is no in-memory component state that survives a navigation. Blazor already gave you typed, declarative access to the two obvious per-request inputs: [SupplyParameterFromQuery] for the URL and [SupplyParameterFromForm] for a POST body. Session was the gap. To read it you cascaded the HttpContext into the component and went through HttpContext.Session yourself, with manual key strings and manual serialization on both sides:

@inject IHttpContextAccessor Http

@code {
    private int CurrentStep;

    protected override void OnInitialized()
    {
        var raw = Http.HttpContext?.Session.GetString("checkout-step");
        CurrentStep = raw is null ? 0 : JsonSerializer.Deserialize<int>(raw);
    }
}

Every component that touched session repeated that ceremony, and the key string was a stringly-typed contract waiting to drift.

What the attribute replaces

Preview 5 collapses the read into a property declaration. The attribute takes a Name for the session key and uses System.Text.Json to serialize and deserialize the value, so it works for any JSON-round-trippable type, not just strings:

@code {
    [SupplyParameterFromSession(Name = "checkout-step")]
    public int CurrentStep { get; set; }
}

The framework reads checkout-step out of the session, deserializes it into int, and assigns it before the component renders. Assigning back to the property writes the new value into the session, so a wizard can advance its step in one line instead of a get, mutate, serialize, set dance.

The plumbing is the standard ASP.NET Core session middleware, so you still wire it up in Program.cs:

builder.Services.AddDistributedMemoryCache();
builder.Services.AddSession();

// ...
app.UseSession();

Where it fits

This is one of several static SSR sharpening passes in Preview 5. It pairs naturally with client-side validation for static SSR forms, which landed in the same release: bind the form’s working state to a session key, validate in the browser, and keep the cheap render mode the whole way through a checkout flow. QuickGrid sorting and pagination now run in static SSR too, so the pattern of “interactive feel, zero circuit” keeps widening.

To try it, install the .NET 11 Preview 5 SDK, target net11.0, and check the ASP.NET Core Preview 5 release notes for the full list.