Check port availability before starting server, provide patterns for killing processes on ports, document automatic port selection strategies, include fallback port ranges, and provide health check patterns. Use when dev server fails to start due to port conflicts.
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Check port availability before starting server, provide patterns for killing processes on ports, document automatic port selection strategies, include fallback port ranges, and provide health check patterns. Use when dev server fails to start due to port conflicts.
Port Conflict Resolution
Overview
Patterns for resolving port conflicts when starting development servers. Check port availability, kill conflicting processes, and use fallback strategies.
Check Port Availability Before Starting Server
Pattern 1: Check Port Before Start
Verify port is available before starting server:
# Check if port is in use
lsof -i :3000
# If port is free, start serverif ! lsof -i :3000; then
npm run dev
elseecho"Port 3000 is in use"fi
Pattern 2: Check Multiple Ports
Check common ports for availability:
# Check common portsfor port in 3000 5173 8080; doif ! lsof -i :$port; thenecho"Port $port is available"breakfidone
Pattern 3: Port Detection Script
Create reusable script:
#!/bin/bash# check-port.sh
PORT=${1:-3000}if lsof -i :$PORT > /dev/null 2>&1; thenecho"Port $PORT is in use"exit 1
elseecho"Port $PORT is available"exit 0
fi
Kill Processes on Ports
Pattern 1: Kill Process by Port
Kill process using specific port:
# Find process using port
lsof -i :3000
# Kill process (replace PID with actual process ID)kill -9 <PID>
# Or one-liner
lsof -ti :3000 | xargs kill -9
Pattern 2: Kill Safely
Check if it's a dev server before killing:
# Check process name
lsof -i :3000 | grep -i "node\|vite\|dev"# Kill only if it's a dev server
lsof -ti :3000 | xargs -I {} sh -c 'ps -p {} -o comm= | grep -i "node\|vite" && kill -9 {}'
Pattern 3: Kill All Node Processes
Kill all node processes (use with caution):
# Kill all node processes
pkill -9 node
# Or more specific
pkill -9 -f "vite\|npm\|node.*dev"
Automatic Port Selection Strategies
Pattern 1: Try Ports Sequentially
Try ports in order until one is available:
# Try ports sequentiallyfor port in 3000 3001 3002 5173; doif ! lsof -i :$port; then
PORT=$port npm run dev
breakfidone
Note: This makes port detection harder - check terminal output for actual port.
Pattern 3: Port Range
Try ports in range:
# Try ports 3000-3010for port in {3000..3010}; doif ! lsof -i :$port; then
PORT=$port npm run dev
breakfidone
Fallback Port Ranges
Common Fallback Ports
Use these ports as fallbacks:
3000: Default for many projects
3001: First fallback
5173: Vite default
8080: Common alternative
4000: Another common choice
Pattern: Fallback Port Selection
# Try common ports
PORTS=(3000 3001 5173 8080 4000)
for port in"${PORTS[@]}"; doif ! lsof -i :$port; then
PORT=$port npm run dev
echo"Server started on port $port"breakfidone
Health Check Patterns
Pattern 1: Poll Server Health
Poll server until ready:
# Poll server healthfor i in {1..10}; doif curl -s http://localhost:3000 > /dev/null; thenecho"Server is ready"breakfisleep 2
done
Pattern 2: Check Health Endpoint
Check health endpoint (if available):
# Check health endpoint
curl -s http://localhost:3000/health
# Or check root
curl -s http://localhost:3000 | head -1
Pattern 3: Wait for Server Message
Wait for server ready message:
# Start server and wait for "Local:" message
npm run dev | grep -m 1 "Local:"
Complete Port Resolution Workflow
Workflow 1: Check and Start
# 1. Check if port is availableif lsof -i :3000; thenecho"Port 3000 is in use"# 2. Try to kill process
lsof -ti :3000 | xargs kill -9
# 3. Wait a momentsleep 1
# 4. Check againif lsof -i :3000; thenecho"Failed to free port, trying alternative"
PORT=3001 npm run dev
else
npm run dev
fielse
npm run dev
fi
Workflow 2: Automatic Port Selection
# Try ports sequentially
PORTS=(3000 3001 5173 8080)
for port in"${PORTS[@]}"; doif ! lsof -i :$port; then
PORT=$port npm run dev &
SERVER_PID=$!
# Wait for server to be readyfor i in {1..10}; doif curl -s http://localhost:$port > /dev/null; thenecho"Server started on port $port"breakfisleep 1
donebreakfidone
Best Practices
Check port before starting: Avoid conflicts
Kill old dev servers: Free up ports
Use fallback ports: Have alternatives ready
Poll for server health: Verify server is ready
Document port usage: Note which port is used
Resources
dev-server-port-detection skill - Port discovery patterns
