v0 chat uses production environment variables and fails to create NeonDB branch

Problem

When creating a new chat for an existing project running on Vercel using the NeonDB integration, a new git branch is created as expected, safeguarding main. However, the chat still uses the same production environment variables the app is running with in production.

Current Behavior

No new NeonDB branch is created (though it works fine when creating a new branch outside of v0).
VERCEL_ENV and NEXT_PUBLIC_VERCEL_ENV are not set to preview or development as expected.
This is dangerous because the development environment pushes migrations on start, which could break production.

The release article does mention new Neon branch creations so I assume something is going wrong on our side or Vercel’s: The New v0 Is Ready for Production Apps and Agents - Neon

Question

How can we proceed to debug this issue?

Hi Vsme,

I’d treat this as a potentially risky env/branch-mapping issue and disable any automatic migration-on-start behavior until you confirm which database the v0 chat is actually using.

A safe way to debug it is to log only the environment and Neon host/branch, not the full connection string or password:

console.log({
  vercelEnv: process.env.VERCEL_ENV,
  publicVercelEnv: process.env.NEXT_PUBLIC_VERCEL_ENV,
  databaseHost: process.env.DATABASE_URL
    ? new URL(process.env.DATABASE_URL).host
    : "missing",
})

If the v0 chat/preview shows production or points at the same Neon host/branch as production, then I would not run migrations from that environment.

In Vercel, I’d also check:

Project Settings → Environment Variables

and confirm whether DATABASE_URL / POSTGRES_URL have separate values for Production and Preview. Preview env vars are used for non-production branches, and branch-specific Preview values can override the general Preview value.

Neon’s Vercel preview integration is supposed to create a preview/<git-branch> branch and inject the connection string into that deployment, so if that branch is not being created, I’d check the Neon integration events and branch limit first:

https://neon.tech/docs/guides/vercel-previews-integration

For now, I’d make the app defensive:

if (process.env.VERCEL_ENV === "production") {
  // never run dev/reset/auto migrations here
}

and only allow destructive or auto migrations when an explicit non-production flag is set, for example ALLOW_PREVIEW_MIGRATIONS=true.

Can you share whether the v0 chat is connected to a Git branch that creates a normal Vercel Preview Deployment, or whether it is running only inside the v0 preview/chat environment?