Localhost not working on Mac: 7 fixes that actually work (2026)

You start your development server, open localhost:3000 in your browser, and... nothing. "This site can't be reached", "ERR_CONNECTION_REFUSED", or an endless loading page. Frustrating, isn't it?

This guide will help you diagnose and fix localhost problems on Mac, step by step.

Quick Diagnosis

Before diving into solutions, let's identify the type of problem:

| Symptom | Likely Cause | Solution | |---------|--------------|----------| | ERR_CONNECTION_REFUSED | Server not started or wrong port | Solution #1 | | Page loads forever | Firewall or timeout | Solution #3 | | localhost OK but domain.local not | Hosts file | Solution #4 | | Worked yesterday, not today | DNS cache or zombie process | Solution #2, #5 |

Solution #1: Check that the server is running

It seems obvious, but this is the most common cause.

Check your terminal

Does your server display "Listening on port 3000" or similar?

# Example with npm
npm run dev

# Expected output
> ready - started server on 0.0.0.0:3000

Check if a process is listening

lsof -i :3000

If nothing appears, no process is listening on that port.

Check the correct port

Make sure you're accessing the right port in your browser. If your server says "port 8080", don't go to localhost:3000.

Solution #2: Free up an occupied port

If you see "Port 3000 already in use", another process is blocking the port.

Identify the process

lsof -i :3000

Result:

COMMAND   PID   USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
node    12345  user   23u  IPv4  0x1234      0t0  TCP *:3000 (LISTEN)

Kill the process

kill -9 12345

Or to kill all processes on a port:

lsof -ti :3000 | xargs kill -9

Solution #3: Check the firewall

macOS firewall or security applications can block local connections.

macOS Firewall

1. Open System Settings > Network > Firewall 2. Click Options... 3. Make sure your application (Node, Python, etc.) is allowed

Third-party applications

Apps like Little Snitch, Lulu, or certain antiviruses can block localhost. Check their rules.

Quick test

Temporarily disable the firewall to test:

sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate off

Don't forget to re-enable it afterwards:

sudo /usr/libexec/ApplicationFirewall/socketfilterfw --setglobalstate on

Solution #4: Check the hosts file

If localhost doesn't resolve to 127.0.0.1, the problem is in the hosts file.

Check the content

cat /etc/hosts

You should see:

127.0.0.1       localhost
::1             localhost

Repair if necessary

If these lines are missing:

sudo nano /etc/hosts

Add:

127.0.0.1       localhost
::1             localhost

Save (Ctrl+O, Enter, Ctrl+X) then flush the DNS cache.

Solution #5: Flush DNS cache

A corrupted DNS cache can prevent localhost from working.

sudo dscacheutil -flushcache && sudo killall -HUP mDNSResponder

Solution #6: Check the listening address

Some servers listen on 127.0.0.1 only, others on 0.0.0.0.

Important difference

• 127.0.0.1: Accessible only from your machine
• 0.0.0.0: Accessible from any interface (useful for Docker, VM)

Force the address in your server

// Node.js / Express
app.listen(3000, '0.0.0.0', () => {
    console.log('Server running');
});

# Python / Flask
app.run(host='0.0.0.0', port=3000)

Solution #7: Tool-specific problems

Node.js / npm

# Clean npm cache
npm cache clean --force

# Delete node_modules and reinstall
rm -rf node_modules package-lock.json
npm install

Docker

# Check that Docker Desktop is running
docker ps

# Restart Docker if necessary
killall Docker && open /Applications/Docker.app

MAMP / XAMPP

1. Check that Apache/Nginx is running (green light) 2. Check the port in preferences (80 vs 8888)

Test with 127.0.0.1 vs localhost

If localhost fails but http://127.0.0.1:3000 works, the problem is in DNS resolution, not your server.

# Test localhost
curl -I http://localhost:3000

# Test direct IP
curl -I http://127.0.0.1:3000

Use custom local domains

Rather than localhost, you can use domains like myproject.test for more clarity.

Prevent future problems

1. Use different ports per project (3000, 3001, 8000, etc.) 2. Stop servers properly (Ctrl+C) instead of closing the terminal 3. Use a manager like Locahl to avoid hosts file conflicts

Conclusion

Localhost problems on Mac usually have simple causes: server not started, port occupied, or stale DNS cache. By following this guide methodically, you should resolve 99% of cases.

If the problem persists, check your application logs and make sure your development environment is properly configured.