> ## Documentation Index
> Fetch the complete documentation index at: https://bun-1dd33a4e-farm-de84d354-pm-sbom.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Deploy a Bun application on Vercel

[Vercel](https://vercel.com/) is a cloud platform for building, deploying, and scaling apps. Vercel Functions can run on the Bun runtime, either behind a framework that Vercel supports or as a [`Bun.serve()`](/runtime/http/server) server.

<Warning>
  The Bun runtime on Vercel is in Beta. Automatic source maps, bytecode caching, and request metrics for `node:http` and
  `node:https` are not supported yet (request metrics for `fetch` are). See [feature
  support](https://vercel.com/docs/functions/runtimes/bun#feature-support) in the Vercel documentation.
</Warning>

***

<Steps>
  <Step title="Configure Bun in vercel.json">
    To run your Functions on Bun, add a [`bunVersion`](https://vercel.com/docs/project-configuration/vercel-json#bunversion) field to your `vercel.json` file:

    ```json vercel.json icon="file-json" theme={"theme":{"light":"github-light","dark":"dracula"}}
    {
    	"bunVersion": "1.x" // [!code ++]
    }
    ```

    The value must be `"1.x"`; Vercel manages the minor and patch versions.

    For best results, match your local Bun version with the version used by Vercel.
  </Step>

  <Step title="Add a server">
    Choose how requests reach your code.

    <Tabs>
      <Tab title="Bun.serve() for the whole app">
        Vercel's Bun framework preset sends every request for the deployment to a single `Bun.serve()` server. Vercel uses the preset when the project sets `bunVersion`, has a `bun.lock` file, and has a server entrypoint at one of these paths:

        * `server.{js,cjs,mjs,ts,cts,mts}`
        * `src/server.{js,cjs,mjs,ts,cts,mts}`

        `bun install` creates `bun.lock` on Bun 1.2 or later. On older versions, run `bun install --save-text-lockfile`. The preset does not detect the binary `bun.lockb` format.

        Call `Bun.serve()` once while the module loads. Vercel detects that call and routes incoming requests to it. The `fetch`, [`routes`](/runtime/http/routing), `error`, and `websocket` options are supported:

        ```ts server.ts icon="https://mintcdn.com/bun-1dd33a4e-farm-de84d354-pm-sbom/IPGjipyt_DGwYrQc/icons/typescript.svg?fit=max&auto=format&n=IPGjipyt_DGwYrQc&q=85&s=4448657ec154e63e3a095030af59c903" theme={"theme":{"light":"github-light","dark":"dracula"}}
        Bun.serve({
        	routes: {
        		"/health": () => Response.json({ status: "ok" }),
        	},
        	fetch() {
        		return new Response("Hello from Bun on Vercel");
        	},
        });
        ```

        A minimal project is `package.json`, `bun.lock`, `server.ts`, and the `vercel.json` from the previous step. It doesn't need an `api/` directory or any routing configuration.

        <Note>
          `port` and `hostname` only apply when you run the server locally; they don't configure the deployed endpoint. Unix sockets and [HTML imports](/runtime/http/server#html-imports) in `routes` are not supported on Vercel.

          To serve WebSocket connections, see the [Bun example in Vercel's WebSockets documentation](https://vercel.com/docs/functions/websockets#bun).
        </Note>
      </Tab>

      <Tab title="Bun.serve() under /api">
        To add a Bun server to a project that also has a frontend, create `api/server.ts` and call `Bun.serve()` once while the module loads. Vercel deploys it as a single Function at `/api/server`. Unlike the framework preset, only requests for `/api/server` reach this server.

        ```ts api/server.ts icon="https://mintcdn.com/bun-1dd33a4e-farm-de84d354-pm-sbom/IPGjipyt_DGwYrQc/icons/typescript.svg?fit=max&auto=format&n=IPGjipyt_DGwYrQc&q=85&s=4448657ec154e63e3a095030af59c903" theme={"theme":{"light":"github-light","dark":"dracula"}}
        Bun.serve({
        	fetch(request) {
        		const url = new URL(request.url);

        		return Response.json({
        			message: "Hello from Bun on Vercel",
        			pathname: url.pathname,
        		});
        	},
        });
        ```

        This only needs the `bunVersion` setting from the previous step; it doesn't use the framework preset or require a `bun.lock` file. To send other paths to this server, add route overrides to `vercel.json`. Each override must use the full request path, including the `/api/server` prefix. See [the Vercel Bun runtime documentation](https://vercel.com/docs/functions/runtimes/bun) for details.
      </Tab>

      <Tab title="Next.js or another framework">
        Frameworks that Vercel supports, such as Next.js, Express, Hono, and Nitro, run on Bun once `bunVersion` is set.

        If you're deploying a **Next.js** project (including ISR), also update the `package.json` scripts so the Next.js CLI runs under Bun:

        ```json package.json icon="file-json" theme={"theme":{"light":"github-light","dark":"dracula"}}
        {
        	"scripts": {
        		"dev": "bun --bun next dev", // [!code ++]
        		"build": "bun --bun next build" // [!code ++]
        	}
        }
        ```

        <Note>
          The `--bun` flag runs the Next.js CLI under Bun. Bundling (with Turbopack or Webpack) is unchanged.
        </Note>
      </Tab>
    </Tabs>
  </Step>

  <Step title="Deploy your app">
    Connect your repository to Vercel, or deploy from the CLI:

    ```bash terminal icon="terminal" theme={"theme":{"light":"github-light","dark":"dracula"}}
    # Using bunx (no global install)
    bunx vercel login
    bunx vercel deploy
    ```

    Or install the Vercel CLI globally:

    ```bash terminal icon="terminal" theme={"theme":{"light":"github-light","dark":"dracula"}}
    bun i -g vercel
    vercel login
    vercel deploy
    ```

    [Learn more in the Vercel Deploy CLI documentation →](https://vercel.com/docs/cli/deploy)
  </Step>

  <Step title="Verify the runtime">
    To confirm your deployment uses Bun, log the Bun version:

    ```ts index.ts icon="https://mintcdn.com/bun-1dd33a4e-farm-de84d354-pm-sbom/IPGjipyt_DGwYrQc/icons/typescript.svg?fit=max&auto=format&n=IPGjipyt_DGwYrQc&q=85&s=4448657ec154e63e3a095030af59c903" theme={"theme":{"light":"github-light","dark":"dracula"}}
    console.log("runtime", process.versions.bun);
    ```

    ```txt theme={"theme":{"light":"github-light","dark":"dracula"}}
    runtime 1.3.14
    ```

    [See the Vercel Bun Runtime documentation for feature support →](https://vercel.com/docs/functions/runtimes/bun#feature-support)
  </Step>
</Steps>

***

* [Fluid compute](https://vercel.com/docs/fluid-compute): Both Bun and Node.js runtimes run on Fluid compute and support the same core Vercel Functions features.
* [Middleware](https://vercel.com/docs/routing-middleware): To run Routing Middleware with Bun, set the runtime to `nodejs`:

```ts middleware.ts icon="https://mintcdn.com/bun-1dd33a4e-farm-de84d354-pm-sbom/IPGjipyt_DGwYrQc/icons/typescript.svg?fit=max&auto=format&n=IPGjipyt_DGwYrQc&q=85&s=4448657ec154e63e3a095030af59c903" theme={"theme":{"light":"github-light","dark":"dracula"}}
export const config = { runtime: "nodejs" }; // [!code ++]
```