PORT 54321 / TCPDev & LocalhostExposure Risk: Low

Port 54321: Supabase Local API (Kong) — Supabase CLI Local REST, Auth, Storage & Realtime Gateway

Default local API gateway port started by `npx supabase start`.

Default Service

Supabase Local API (Kong)

Process: docker-proxy (kong)

Transport Protocol

TCP

IANA Registered Port 54321

Docker Port Flag

-p 54321:8000

Container to Host Mapping

How to Check & Kill Process on Port 54321 (EADDRINUSE Fix)

macOS & Linux (lsof / kill)

# Find process using port 54321
sudo lsof -i :54321

# Instantly kill process on port 54321
lsof -ti:54321 | xargs kill -9

Windows (PowerShell & CMD)

# Find PID listening on port 54321
netstat -ano | findstr :54321

# Force kill by PID
taskkill /PID <PID_NUMBER> /F

Cross-Platform Node.js One-Liner

# Kill port 54321 via npx
npx kill-port 54321

# Or diagnose via Castov CLI
npx castov fix "EADDRINUSE :::54321"

Linux Firewall (UFW) & Connectivity Test

# Test if port 54321 is reachable
nc -zv localhost 54321

# Allow or deny port 54321 in UFW
sudo ufw allow 54321/tcp

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Frequently Asked Questions about Port 54321

What is Port 54321 used for?

Port 54321 is the standard network port for Supabase Local API (Kong) (Supabase CLI Local REST, Auth, Storage & Realtime Gateway) operating over TCP. The typical system daemon or process is docker-proxy (kong).

How do I kill a process running on Port 54321 (EADDRINUSE)?

On macOS and Linux, run: lsof -ti:54321 | xargs kill -9 (or npx kill-port 54321). On Windows PowerShell/CMD, run: netstat -ano | findstr :54321 and then taskkill /PID <PID> /F.