Jun 4, 2026 · Databases · 1min read

mongodb://localhost:27017 — Connect & Run MongoDB Locally

What does mongodb://localhost:27017 mean? URI examples, mongosh and Compass, Docker startup, and fixes for ECONNREFUSED.

Seeing mongodb://localhost:27017 or mongodb localhost 27017 means an app expects MongoDB on this machine (default port 27017). It is a client connection string, not a web page — opening it in Chrome will not show a site.

Connection string cheat sheet

Use	URI
Default (no auth)	`mongodb://localhost:27017`
With database	`mongodb://localhost:27017/mydb`
Via IP	`mongodb://127.0.0.1:27017/mydb`
With credentials	`mongodb://user:pass@localhost:27017/mydb?authSource=admin`
Trailing slash	`mongodb://localhost:27017/`

Common env keys: MONGODB_URI, MONGO_URL, DATABASE_URL.

Port guide: localhost ports §27017.

Verify with a client

mongosh

mongosh "mongodb://localhost:27017"
use mydb
db.users.insertOne({ name: "Alice" })
db.users.find()

MongoDB Compass

Paste mongodb://localhost:27017 → Connect.

In code

await mongoose.connect('mongodb://localhost:27017/myapp');

Stack	Notes
NestJS	`@nestjs/mongoose`
Express	`mongoose.connect(...)`
Next.js	`MONGODB_URI` in `.env`

Install & start

macOS: brew install mongodb-community → brew services start mongodb-community

Docker:

docker run -d --name mongo -p 27017:27017 mongo:7

Troubleshooting

ECONNREFUSED 127.0.0.1:27017 — MongoDB not running; check lsof -i :27017; ensure the URI includes the mongodb:// scheme.
Auth errors — add user + authSource if auth is enabled.
Docker vs host — confirm -p 27017:27017; use service names between containers.

See port-conflicts, Redis.

Summary

mongodb://localhost:27017 = local MongoDB default. Confirm with mongosh/Compass, then reuse the same URI in your app.