Question about Database connection string

[raadtotheraad]

Question

Hi there,

Does Prisma automatically add :5432 to the localhost?

Example i set it to localhost, does it set it to localhost:5432?

Thanks

How to reproduce (optional)

No response

Expected behavior (optional)

No response

Information about Prisma Schema, Client Queries and Environment (optional)

No response

[sueun-dev]

Yeah, Prisma fills in 5432 when you leave the port off. Just tested on 6.19.3: with postgresql://postgres:pw@localhost/testdb (no port) it errors P1001 Can't reach database server at localhost:5432, and the exact same URL with :5544 connects fine against the same db. So localhost really does resolve to localhost:5432 under the hood.

It's baked into the connection parser (quaint): port() returns self.url.port().unwrap_or(5432), and the host defaults to localhost the same way. So for a normal local Postgres you can drop the port and it just works. Only set it explicitly if your server listens on something other than 5432.

[jibin7jose]

Reply: Database connection string

Yes, for a PostgreSQL datasource Prisma defaults to port 5432 when the port is omitted from the connection string.

So if you write:

postgresql://user:password@localhost/dbname

Prisma treats it as:

postgresql://user:password@localhost:5432/dbname

Why this happens

Prisma uses PostgreSQL's standard default port. The Prisma codebase also reflects this default directly in its connection handling, where PostgreSQL resolves to 5432 if no port is provided.

When to set the port explicitly

Set the port yourself if:

• your database is not running on 5432
• you are connecting to a container or a managed service using a custom port
• you want the connection string to be fully explicit for clarity

Short answer

If you leave the port off, Prisma will use 5432 for PostgreSQL.

Official docs:

• Prisma connection URLs

[JosephHampton]

Yeah it does. If you leave the port off, the Postgres driver just falls back to its default, which is 5432. So these two end up being the same thing:

postgresql://user:pass@localhost/mydb
postgresql://user:pass@localhost:5432/mydb

localhost with no port becomes localhost:5432.

Couple of things worth keeping in mind:

• It only fills in the default. If your Postgres is on a different port (Supabase's pooler is on 6543, or if you mapped something like 5433 in Docker) you have to write the port yourself, there's no auto detection.
• It's not really a Prisma thing, it's just how the Postgres protocol works. Prisma passes the URL straight to the driver and Postgres assumes 5432 when nothing is given (MySQL would assume 3306, and so on).

So for a normal local Postgres you're fine leaving :5432 off.

Hope that clears it up. If it was useful it'd be great if you could mark it as the answer 🙏

[raadtotheraad]

Thanks!