Screen Sharing cannot connect to another Mac

The other Mac must have Screen Sharing on and allow your user. Both Macs must be awake, on the same network, with port 5900 open.

Fix this with your agentCopies a prompt for Claude Code, Codex or any agent that can use Terminal.

My Mac has this problem: Screen Sharing cannot connect to another Mac. Read https://kilobat.app/guides/screen-sharing-not-connecting-mac.md and work through it with me. Install the Kilobat CLI if it’s missing: brew install seifip/kilobat/kilobat. Run the guide’s Terminal and kilobat checks yourself and tell me what you find. List the steps only I can do. Ask before you change any setting.

Applies to: macOS 13 Ventura and later for System Settings. High Performance needs Apple silicon and macOS Sonoma 14 or later on both Macs.Checked: 7 November 2026

Symptoms

The other Mac does not appear under Network in the Screen Sharing app.
The connection waits and then fails.
You can connect by name on one network, but not on another.
The High Performance option does not appear, or the session falls back.

Likely causes

Screen Sharing is off on the other Mac. Apple says that the Mac you want to access must have Screen Sharing or Remote Management on.
Screen Sharing and Remote Management conflict. Apple says that you cannot have both on at the same time.
Your user is not allowed. The user must be in the access list of Screen Sharing on the other Mac.
A Mac is asleep. Apple says to make sure that neither Mac is in sleep.
The Macs are on different networks. Apple says to make sure that both computers are connected to the same network.
The firewall. Apple says that Block all incoming connections stops connections to sharing services.
High Performance needs more. Apple asks for high bandwidth, low latency and UDP ports 5900, 5901 and 5902 between the Macs.

How to check

On the other Mac, choose Apple menu > System Settings > General > Sharing.
Look at Screen Sharing and Remote Management. Only one of them can be on.
Click the Info button next to Screen Sharing. Look at Allow access for.
Make sure that both Macs are awake and on the same network.
On the other Mac, show whether the firewall blocks all incoming connections.
```
/usr/libexec/ApplicationFirewall/socketfilterfw --getblockall
```
From your Mac, test whether port 5900 answers. Use the other Mac's IP address.
```
nc -vz -G 5 192.168.1.20 5900
```

How to fix it

If Remote Management is on and you use Screen Sharing, turn off Remote Management first.
Turn on Screen Sharing.
In Allow access for, choose All users, or add your user to Only these users.
Change the sleep settings of the other Mac so that it stays awake.
If Block all incoming connections is on, turn it off in Network > Firewall > Options.
Connect both Macs to the same network. Then open the Screen Sharing app.
Click the New Connection button. Enter the hostname of the other Mac.
For High Performance, use a wired network connection, as Apple recommends.

With Kilobat

Test the TCP connection to port 5900. Read the IPv4 line. It says connected, refused or no answer.
```
kilobat why 192.168.1.20:5900
```
The check then tries a secure web connection. Screen Sharing does not use it, so ignore that step.
Check whether devices on this network can see each other. Some guest networks isolate them.
```
kilobat local check
```
List the devices that the Mac talked to recently, with Bonjour names.
```
kilobat devices --bonjour
```
After a session that lagged, Kilobat writes a report with the cause. Show the reports for remote desktops.
```
kilobat remote --kind desktop
```

Questions

Which ports does Screen Sharing use?

Apple lists TCP and UDP port 5900 for Screen Sharing. High Performance also needs UDP 5901 and 5902.

Can I use both Screen Sharing and Remote Management?

No. Apple says that only one can be on. Apple says that either one lets you share the screen.

Why is High Performance missing?

Apple says that it needs Apple silicon and macOS Sonoma 14 or later on both Macs. One session can run on each Mac at a time.

Sources

Apple Support: Turn screen sharing on or off on Mac
Apple Support: Share the screen of another Mac
Apple Support: If you can't share Mac computer screens
Apple Support: Screen sharing type options on Mac
Apple Support: TCP and UDP ports used by Apple software products
Apple Support: Change Firewall settings on Mac
nc(1) and socketfilterfw(8), man pages installed with macOS 27.2

Checked on 7 November 2026.