Hono API on Vercel crashes with ERR_MODULE_NOT_FOUND when importing server files

Help vercel • hono • serverless

Summary

I deployed a full-stack application using Hono for the API and Vite/React for the frontend. The deployment succeeds, but I can only the serverless function crashes in the preview page.

From the logs, it appears Vercel cannot resolve a module imported from outside the /api directory.

Project Setup

My project structure looks like this:

1honno-react-demo2│3├ api4│   └ index.ts5│6├ server7│   ├ app.ts8│   └ routes9│       └ expenses.route.ts10│11├ frontend12│   ├ src13│   └ dist14│15└ package.json

The API entry file is:

/api/index.ts

1import app from "../server/app";2import { handle } from "hono/vercel";34export const GET = handle(app);5export const POST = handle(app);6export const PUT = handle(app);7export const PATCH = handle(app);8export const DELETE = handle(app);9export const OPTIONS = handle(app);

My Hono app is defined in:

/server/app.ts

1import { Hono } from "hono";2import { logger } from "hono/logger";3import { expensesRoute } from "./routes/expenses.route";45const app = new Hono();67app.use("*", logger());89const apiRoutes = app10  .basePath("/api")11  .route("/expenses", expensesRoute);1213export default app;14export type ApiRoutes = typeof apiRoutes;

Current Behavior

The deployment completes successfully and the frontend loads, but when I call the API endpoint:

1/api/expenses/total-spent

the request returns:

1500: INTERNAL_SERVER_ERROR2Code: FUNCTION_INVOCATION_FAILED

Serverless Function Logs

1Error [ERR_MODULE_NOT_FOUND]: Cannot find module '/var/task/server/app'2imported from /var/task/api/index.js

So it seems the serverless function cannot resolve:

1../server/app

What I’ve Tried

Verified that the path is correct locally
Confirmed the app works locally using vercel dev
Removed any Bun-specific imports (hono/bun)
Checked that hono is listed in dependencies

Questions

Does Vercel serverless only bundle files inside /api by default?
Should the Hono app be moved into the /api directory?
Is there a recommended structure for deploying a Hono API with Vercel?

Any guidance would be greatly appreciated. Thank you!

Here is the link to my repository: https://github.com/lancer751/hono-bun-react--demo