Vercel Python Services

# Python Services with Vercel

Build multi-service projects using Vercel's `experimentalServices` API with a Python backend and (optional) JavaScript frontend.

## Setup

1. Create the project files (see references for the minimal working example). Choose frameworks for each service according to user's requests.
2. Define backend routes without the `/api` prefix (e.g. `@app.get("/health")`). Vercel strips the prefix before forwarding to the backend.
3. Validate services in `vercel.json` have `entrypoint` and `routePrefix`, but no extra unknown fields, otherwise that will cause preview to crash

Only `vercel.json` lives at the root. Each service manages its own dependencies independently.

## Usage

- Use `vercel dev -L` from the project root to run all services as one application. The CLI will handle each individual service's routing and dev server and put the application on port 3000.
- Frontend calls `/api/...` — Vercel routes these to the backend, which sees only the path after the prefix. No localhost URLs, no proxy needed.


3.12


import fastapi
import fastapi.middleware.cors

app = fastapi.FastAPI()

app.add_middleware(
    fastapi.middleware.cors.CORSMiddleware,
    allow_origins=["*"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)


@app.get("/health")
async def health() -> dict[str, str]:
    return {"status": "ok"}


[project]
name = "backend"
version = "0.1.0"
description = "FastAPI backend service"
requires-python = ">=3.12"
dependencies = [
    "fastapi[standard]>=0.128.1",
]


{
  "name": "frontend",
  "private": true,
  "type": "module",
  "scripts": {
    "dev": "vite",
    "build": "vite build"
  },
  "dependencies": {
    "react": "^19.2.0",
    "react-dom": "^19.2.0"
  },
  "devDependencies": {
    "@vitejs/plugin-react": "^5.1.1",
    "typescript": "~5.9.3",
    "vite": "^7.2.4"
  }
}


import { defineConfig } from 'vite'
import react from '@vitejs/plugin-react'

export default defineConfig({
  plugins: [react()],
})


{
  "experimentalServices": {
    "frontend": {
      "entrypoint": "frontend",
      "routePrefix": "/"
    },
    "backend": {
      "entrypoint": "backend/main.py",
      "routePrefix": "/api"
    }
  }
}