Swap.Htmx

Welcome to Swap.Htmx

Swap.Htmx Team January 11, 2026 3 min read
swap.htmx htmx aspnetcore mvc server-driven

Swap.Htmx is an opinionated way to build interactive ASP.NET Core apps while keeping the web simple: controllers return HTML, HTMX swaps it in, and the server coordinates UI updates.

If you’ve ever felt like you had to pick between:

  • “plain MVC” (simple, but harder to keep rich UIs consistent), or
  • a full SPA (powerful, but adds build tools + client state + duplicated logic),

Swap.Htmx sits in the middle: server-driven UI with first-class ergonomics for partial updates.

What is Swap.Htmx?

Swap.Htmx is an open-source .NET library for building server-driven web apps using server-rendered HTML. It pairs naturally with HTMX (https://htmx.org) to bring interactivity to your pages without adopting a JavaScript framework.

At a high level:

  • You return HTML from controllers (full pages or partials).
  • HTMX handles the browser-side swapping.
  • Swap.Htmx helps you coordinate multi-part UI updates, UI events, and server-side UI state.

The core idea: one action, multiple UI updates

In real apps, one user action often affects more than one piece of UI: a list, a counter, a toast message, a preview panel, etc.

Swap.Htmx makes it straightforward to respond to one request with multiple updates, without wiring up a client-side state store.

Here’s the mental model:

return SwapResponse()
    .WithView("_ProductCard", product)
    .AlsoUpdate("cart-count", "_CartCount", count)
    .WithSuccessToast("Added to cart!")
    .Build();

(That’s a conceptual example — the point is the shape of the response: multiple updates from one server action.)

What you get out of the box

A few highlights you’ll see throughout the docs:

  • SwapView(): return one result that works for both full navigations and HTMX requests.
  • SwapResponse(): update multiple targets in a single response (including toasts and triggers).
  • Events / handlers: decouple “what happened” from “what parts of the UI need to update.”
  • SwapState: keep UI state (filters, pagination, wizards) on the server and persist it through hidden fields.
  • Type-safe helpers: source generators can reduce magic strings for views, element IDs, and event keys.

Who is this for?

Swap.Htmx is a great fit if you:

  • build ASP.NET Core MVC/Razor apps,
  • like server-rendered HTML,
  • want rich interactivity without managing a lot of client-side state.

It’s not trying to replace every use of JavaScript. The goal is to remove the need for a full JavaScript framework for a large class of apps.

Next steps