Bug Report: Neon Serverless WebSocket Pooling - Pool doesn't pass connectionString to internal connections

I recently encountered a critical bug in @neondatabase/serverless that completely broke my Prisma integration. Here's what happened and how to identify if you're affected.

Environment

• @neondatabase/serverless: 1.0.2
• @prisma/adapter-neon: 7.0.1
• @prisma/client: 7.0.1
• Node.js: 25.2.1
• OS: Windows

The Problem

When using Pool from @neondatabase/serverless with WebSocket pooling enabled, the Pool constructor accepts a connectionString parameter but does NOT pass it to internal connection clients created by Un.newClient().

This causes all Prisma queries to fail with:

Error: No database host or connection string was set, and key parameters have default values
(host: localhost, user: Admin, db: Admin, password: null).
Is an environment variable missing?

Code That Fails

import { Pool, neonConfig } from "@neondatabase/serverless";
import { PrismaNeon } from "@prisma/adapter-neon";
import { PrismaClient } from "@prisma/client";
import ws from "ws";
 
neonConfig.webSocketConstructor = ws;
neonConfig.pipelineConnect = "password";
 
const pool = new Pool({ connectionString: process.env.DATABASE_URL });
const adapter = new PrismaNeon(pool);
const prisma = new PrismaClient({ adapter });
 
// Query fails - pool doesn't pass connectionString to internal clients
await prisma.project.create({ data: { name: "test" } });

Root Cause

The issue lies in how Pool creates internal connections. When Un.newClient() is called, it creates new WebSocket connections without inheriting the Pool's connectionString configuration.

Instead of using the provided DATABASE_URL, it falls back to default localhost parameters:

• Host: localhost
• User: Current system user (e.g., Admin)
• Database: Current system user (e.g., Admin)
• Password: null

Stack Trace

at kn.connect (node_modules/@neondatabase/serverless/index.mjs:1316:50)
at Un.newClient (node_modules/@neondatabase/serverless/index.mjs:1118:85)
at Un.connect (node_modules/@neondatabase/serverless/index.mjs:1115:1)
at PrismaNeonAdapter.performIO (node_modules/@prisma/adapter-neon/dist/index.mjs:523:40)

Expected vs Actual Behavior

Expected: Pool should pass connectionString to all internal WebSocket connection clients created via Un.newClient().

Actual: Pool creates connections with default localhost parameters, completely ignoring the provided connectionString.

Impact

This bug makes it impossible to use Prisma with Neon Serverless WebSocket pooling in its current state. Any application relying on this setup will experience complete database connectivity failure.

Video Demonstration

I've documented this issue in detail. Watch the full demonstration:

You can also view the post on X (Twitter): Watch on X →

Workarounds

Until this is fixed in the upstream package, you may need to:

1. Use direct connections instead of pooling
2. Set connection parameters individually instead of using connectionString
3. Wait for a patch from the Neon team

Reporting

This issue needs to be reported to:

• @neondatabase/serverless GitHub repository
• Neon community forums

If you're experiencing similar issues, please upvote and comment on the bug report to help prioritize a fix.

Update: If you've found a solution or workaround, please share it in the comments or reach out on X @FrostbytHitsuG.