--- last_modified: 2026-06-16 title: "HTTP serving" description: "How Deno.serve() works inside a desktop app: automatic port binding, the DENO_SERVE_ADDRESS env var, and serving local UI to the embedded webview." --- :::info Coming in Deno 2.9 `deno desktop` ships in Deno v2.9.0 and is not in a stable release yet. To try it now, run `deno upgrade canary` to install the [`canary`](/runtime/reference/cli/upgrade/) build. The command, configuration keys, and TypeScript APIs may still change before the feature is stable. ::: A `deno desktop` app serves its UI over local HTTP and points the embedded webview at it. This keeps the app structure identical to a normal Deno website. [`Deno.serve()`](/api/deno/~/Deno.serve) is the entry point and every request flows through your handler, but with no port to manage and no remote network exposure. ## How it works When the binary starts: 1. The runtime picks an unused local port and sets the `DENO_SERVE_ADDRESS` environment variable to `tcp:127.0.0.1:`. 2. Your code calls `Deno.serve(...)`. The serve API reads `DENO_SERVE_ADDRESS` (set by Deno itself in this mode, not by the user) and binds to that port, ignoring whatever port you pass. 3. The webview navigates to `http://127.0.0.1:` once the listener is ready. You write the same handler you would for any Deno HTTP server. There is no desktop-specific serving API. ```ts title="main.ts" Deno.serve((req) => { const url = new URL(req.url); if (url.pathname === "/api/hello") { return Response.json({ hello: "world" }); } return new Response(HOMEPAGE, { headers: { "content-type": "text/html" }, }); }); const HOMEPAGE = `

Hello, desktop

`; ``` ```sh deno desktop main.ts ``` The default-export form works too: ```ts title="main.ts" export default { fetch(req: Request): Response { return new Response("Hello!"); }, }; ``` ## Why local HTTP? The local-HTTP architecture trades a tiny amount of overhead for properties that matter for desktop apps: - **Same code in browser and desktop.** The homepage, fetch, websockets, and cookies all behave identically in `deno run` and `deno desktop`. You can develop in a browser tab and ship the same code as a desktop binary. - **No special module system.** Imports, static assets, and module-level code all run the way they would for a web server. - **Frameworks run unchanged.** Next.js, Astro, Fresh, and others already ship a production HTTP server. `deno desktop` runs that server and points the webview at it. See [Frameworks](/runtime/desktop/frameworks/). The cost is a single network hop within `127.0.0.1` per request. For UI serving (HTML, CSS, bundled JS, JSON API responses) this is negligible. For high-throughput Deno → webview communication where the overhead matters, use [bindings](/runtime/desktop/bindings/), which bypass HTTP entirely and route through in-process channels. ## Network exposure The bound address is **always** `127.0.0.1` (or `[::1]`). The compiled binary never binds to a public interface, even if you pass `0.0.0.0` to [`Deno.serve()`](/api/deno/~/Deno.serve). Other apps and other users on the same machine cannot reach your server. If you need to serve users on other machines (a self-hosted local server), do not use `deno desktop` for that part of your stack. Use `deno run` with an explicit address, or build a separate service. ## Custom port behavior You cannot override the port [`Deno.serve()`](/api/deno/~/Deno.serve) binds to inside `deno desktop`. This is intentional: the webview needs to navigate to the same port the runtime is listening on, and the runtime is the source of truth for that value. If you need to know where the server is bound, read `DENO_SERVE_ADDRESS`. It is in `tcp:127.0.0.1:` form, so split off the port when you need an `http://` URL: ```ts const addr = Deno.env.get("DENO_SERVE_ADDRESS"); // "tcp:127.0.0.1:54321" const port = addr.split(":").pop(); console.log("Serving on:", `http://127.0.0.1:${port}`); ``` ## Serving multiple windows When you create additional [windows](/runtime/desktop/windows/), they all load from the same local HTTP server by default. Use different paths per window to differentiate: ```ts const port = Deno.env.get("DENO_SERVE_ADDRESS").split(":").pop(); const settings = new Deno.BrowserWindow(); settings.navigate(`http://127.0.0.1:${port}/settings`); ```