Assetto Corsa Server Not Showing or Can't Join (AssettoServer Fixes)

When an Assetto Corsa server does not show in Content Manager or drivers cannot get in, the cause is nearly always one of six things: REGISTER_TO_LOBBY is off, the TCP, UDP or HTTP port is not reachable, the driver is missing a car or track (or has a different version of it), their Custom Shaders Patch is too old for the server, the entry list has no free car of the model they picked, or the password is wrong. The server console tells you which one in most cases, so read it while a friend tries to join.

Quick checklist

Cause 1: the server never registers to the lobby

Content Manager builds its Online list from the Kunos lobby. A server only appears there if it asks to be listed. Open cfg/server_cfg.ini and check the [SERVER] section:

[SERVER]
NAME=Night Cruise | Traffic
REGISTER_TO_LOBBY=1
UDP_PORT=9600
TCP_PORT=9600
HTTP_PORT=8081

With REGISTER_TO_LOBBY=0 the server still runs, but only people who add it by address can see it. After a restart, watch the console: AssettoServer logs whether lobby registration worked. If it reports a failure, the lobby could not reach your HTTP port, which brings you to cause 2.

Give it a minute or two after the start before you search. Then type part of the server name in the Online tab's search box rather than scrolling, because the list holds thousands of servers.

Cause 2: one of the three ports is closed

An Assetto Corsa server uses three ports, and all three must be reachable from the internet:

The classic pattern is a server that shows in the list (HTTP works) but nobody can finish joining (TCP or UDP blocked), or one where the host can join from the same PC but friends cannot. Forward all three on your router to the machine running the server, and allow the server program through Windows Defender Firewall on both private and public networks. Our port forwarding guide has the router side.

If the ports are forwarded and still look closed from outside, your connection may be behind carrier grade NAT, where port forwarding cannot work at all. The check takes a minute: see how to tell if you are behind CGNAT.

AssettoServer also has an EnableUPnP option in extra_cfg.yml. It can open ports on routers that allow UPnP, but a manual forward is more predictable.

Cause 3: missing or different content

Assetto Corsa compares checksums of the car data and track files when a driver connects. If the driver has a different version of a mod car, or the track's models or surface files differ, they get kicked during loading. Content Manager marks missing content in the server's detail view before you join, and can download much of it if the server owner shared links.

Fixes, in order:

1. Make sure every driver has the exact same car folders and the same track version the server runs. Mod tracks get updated, and a driver on last year's version will not pass.
2. When you change content on the server, re-pack it in Content Manager and upload the new pack, rather than copying single folders by hand.
3. Folder names must match exactly. CARS= in server_cfg.ini uses the folder name, not the display name.

If you are still adding content, our guide on adding cars and tracks to an Assetto Corsa server covers the packing step and the checksum details.

Cause 4: Custom Shaders Patch is too old or missing

AssettoServer can require a minimum CSP version, set by MinimumCSPVersion in extra_cfg.yml. Freeroam servers often require a recent build because AI traffic, weather and client messages depend on it. A driver below that version is refused before the track loads. Some owners also force it through the track line:

TRACK=csp/2144/../shuto_revival_project_beta

The number after csp/ is a CSP build ID, and any client below it cannot join. The fix is on the driver's side: update CSP in Content Manager under Settings, Custom Shaders Patch. If you want to let older clients in, lower MinimumCSPVersion or remove the csp/ prefix, and accept that some features will not work for them.

Cause 5: no free slot for that car

"No free slots" or "no available slots" when the server is clearly not full means the entry list has no unused entry of the car model the driver selected. Each [CAR_n] block in entry_list.ini is one seat in one specific model. Three entries of an E30 and two drivers already in E30s means the third driver gets one slot, and a fourth gets refused.

[CAR_0]
MODEL=bmw_m3_e30
SKIN=
AI=none

[CAR_1]
MODEL=bmw_m3_e30
SKIN=
AI=none

Add more entries of the popular cars, keep the CAR numbers in sequence with no gaps or duplicates, and stay within the track's pit box count. On traffic servers, remember that AI traffic cars also take entries.

Cause 6: wrong password, ping kicks and Steam auth

• Password. PASSWORD= in server_cfg.ini is the join password, ADMIN_PASSWORD= is for admins. Drivers enter the join password in Content Manager's join dialog. A trailing space in the file is enough to break it.
• Ping limit. MaxPing and MaxPingSeconds in extra_cfg.yml kick drivers whose ping stays above the limit. A driver on the far side of the world can be kicked after a few seconds of driving. Raise the limit if your group is spread out.
• Steam auth. With UseSteamAuth: true, AssettoServer validates each driver's Steam ticket. That needs CSP and a recent Content Manager. Drivers on an old setup, or using a non Steam copy, will be refused. Turn it off only if you understand that it also stops spoofed Steam IDs.

If one driver fails and everyone else is fine

Then the server is fine and the problem is on that PC. Have them update Content Manager and CSP, verify the game files in Steam, check that their antivirus is not blocking acs.exe, and remove any VPN. A driver who can join other freeroam servers but not yours almost always has a content version mismatch, so compare the car and track versions first.

Skip the router part

Causes 1 and 2 are mostly about home networking. A GamezServers Assetto Corsa server runs AssettoServer with its own public address and its ports already open, the server name, password, admin password and max clients are fields in the control panel, and the live console shows lobby registration and every kick reason as it happens. You still pick the content, upload your Content Manager pack over SFTP and set up the entry list, but nobody's PC has to stay on. New customers get 50% off the first month.

FAQ

Why is my Assetto Corsa server not in the Content Manager list?

Usually REGISTER_TO_LOBBY is 0 or the HTTP port is not reachable from outside. Set it to 1, open the HTTP port as TCP, restart and search the name in the Online tab.

What ports does an Assetto Corsa server need?

Three: the TCP port and UDP port set in server_cfg.ini (often the same number) and the HTTP port, which is TCP. All three must be open.

Why does Assetto Corsa say checksum mismatch?

The driver's car or track files are not identical to the server's. Install the same version of the mod, or have the server owner re-pack and share the content.

Can drivers join without Custom Shaders Patch?

Only if the server does not require it. Freeroam servers with AI traffic usually set a minimum CSP version, so drivers without it are refused.

Why does it say no free slots when the server is half empty?

The car model they picked has no unused entry in entry_list.ini. Add more entries of that car or pick another model.