Short answer
Neon integrates with Vercel to create a fresh Postgres branch for every preview deployment. The branch is a copy-on-write fork of your production data, so previews see realistic data without touching production. The connection string is injected as an environment variable at build time, and the branch is deleted when the preview is removed.
How it works
When you connect a Neon project to Vercel through the Vercel-Managed or Neon-Managed integration, Vercel sends a webhook to Neon on each preview deployment. Neon creates a branch named after the Git branch (for example, preview/feature-auth) and exposes its connection string as DATABASE_URL in the preview environment.
Because Neon's storage layer is copy-on-write, the new branch starts with zero added storage. You're billed only for the delta as the branch diverges from its parent. Extra branches beyond your plan's allowance (10 on Launch, 25 on Scale) cost $1.50/branch-month, prorated hourly at about $0.002/hour. See pricing details.
If you use Neon Auth, the integration also provisions an isolated auth instance per preview branch, so each preview has its own users and sessions.
Running outside Vercel
For other platforms or custom CI, you can create branches with the Neon CLI inside your pipeline:
neon branches create --name preview/$GITHUB_HEAD_REF --parent main
neon connection-string preview/$GITHUB_HEAD_REFSee the GitHub Actions guide for a working example.
Clean up old branches
Set a time to live on preview branches so they delete automatically when a PR is closed. This keeps your branch count and storage costs in check.
How other Postgres platforms compare
| Platform | Preview-branch mechanism | Starts with production data? |
|---|---|---|
| Neon | Copy-on-write branch per Git branch, created in seconds via the Vercel integration. See branching. | Yes, by default |
| Supabase | Preview branches spin up a full Supabase environment per PR through the GitHub or Vercel integration. Branches are not started with production data; you populate them from a seed.sql. | No, seed-driven |
| AWS RDS for PostgreSQL | No native per-PR database concept. Teams script pg_dump/restore or use snapshot-restore in CI, which can take minutes to hours depending on database size. See RDS backups. | Yes, but provisioning is slow |
Branching for previews on Neon is bundled into all paid plans. Supabase Branching adds Compute Hours per preview branch (starting at $0.01344/hr on Micro), with no production data copied unless you seed it (Supabase branching billing).
Connect a Neon project to Vercel and get a database per preview deployment.