Totally Safe Moon Project Multiplayer and Co-op Guide

Totally Safe Moon Project supports solo play and online co-op only, with no split-screen. The Steam page says up to 4 players (you plus 3 friends), but a developer confirmed in the Steam forums on launch day that the cap is actually 5 players (you plus 4 friends) and cannot be raised. You invite friends from the garage at the start of a run, and everyone builds the same tower together; there is no competitive mode.

How many players?

This is the most-asked multiplayer question, and the official sources do not agree:

Source	Player count
Steam store description	"solo or with up to 3 friends" (4 total)
Developer post on Reddit, May 2026	"online co-op with up to 4 friends"
Developer reply on Steam forums, Oct 30, 2026	"a limit of 5 players (you + 4 friends) and this can't be changed", limited "to avoid synchronization issues"

Other players in that thread asked the developers to update the store text to match. Until they do, four players is the safe expectation and five is worth trying. Most recorded co-op videos, including Geeky Pastimes' full clear, used four players.

Online only, no split-screen

Steam's official feature list includes Single-player, Multi-player, Co-op and Online Co-op. It does not list local co-op or split-screen. "Split Screen" appears among the user-applied tags on the store page, but tags are added by players and are not a feature guarantee.

How to invite friends

The official Steam screenshots show an Invite Friends button inside the starting garage and an on-screen prompt "Press I to invite friends". The host starts a game and invites people from there. One streamer (More Galixcey) also had viewers join by sharing a code from his game, so a join code appears to be another option for public sessions. Gather everyone at the marked exit spot in the garage before you start the run.

What changes in co-op

• You can pick up each other. The Gravity Gun grabs players as well as objects. There is an achievement for it (I'm the Boss!) and one for throwing a friend off the tower from above 125 m (This Is Sparta!). A grabbed player cannot move or look around until released.
• Reviving. With fall damage on, a player who takes a big fall gets knocked down. A teammate can revive them by holding E nearby; otherwise they respawn on the ground after a few seconds.
• Shared progress. Everyone builds the same tower and the same points pay for upgrades at the terminal.
• Moon arrivals. In the ending, recorded runs show a counter of how many players have reached the Moon (for example "three out of four").

Co-op building tips

1. One builder, several haulers. Put one player at the top and have the others pass fences, cars and houses into reach. Streamers who did this said it sped things up massively.
2. Call out what you are standing on. Most co-op disasters in recorded runs happen when someone grabs the car or bus a teammate is using.
3. Keep the umbrella handy. Players get knocked off by friends, UFOs and asteroid rain all the time.
4. Split jobs late game. One player places Oxygen Totems, another carries the laser, others keep the route repaired.
5. Be careful with fireworks and the magnet. Both can fling teammates off the tower.

For the full route, see the walkthrough. For what each tool does, see upgrades and tools.

Can you play it solo?

Yes. Single-player is an official feature, and nothing in the main objective requires a second player. Solo runs just take longer because you have to haul every object yourself.