How to Install Alien Swarm and Join a Server

Someone on your team is going to weld a door shut with you on the wrong side of it. Not out of malice. The aliens were coming down the corridor and the welder was in their hands, and now you are alone on the far side of a sealed door with a pistol.

That is Alien Swarm in one image. Four marines in one corridor, holding a set of tools that work on your own squad exactly as well as they work on the swarm.

The game is a top-down co-operative shooter that Valve put on Steam for free, built on the Source engine. You look down on your marine from above. You move with the keyboard and aim with the mouse, and the goal is getting four people to the end of a mission alive. There are 6 servers listed here, which is a small number and worth saying plainly at the top: this is a game you arrange to play with people, not one you drop into at random on a Tuesday afternoon.

What you need

An account and the Steam client, and that is the whole list. Alien Swarm is free. There is no separate launcher, no account tied to a publisher, no store page that asks for money halfway through.

If Steam itself is new to you, our guide to downloading and installing Steam covers making an account and locking it down before you attach anything to it.

Hardware is not a conversation. The game came out of an era when a mid-range laptop was a serious machine, and it runs on essentially anything now. The camera sits above the action, so you are not pushing a high frame rate for aim the way you would in a first-person shooter. Comfortable is enough.

Two games with almost the same name

Search Steam for Alien Swarm and you will find more than one result. This trips people up constantly, so deal with it before you install anything.

The original release is Valve's. There is also a community-developed continuation that lives as its own separate entry on Steam, free as well, with its own campaigns and its own player base. They are not the same application. A server running one of them is not reachable from the other, and a friend who says "I'm on Alien Swarm" has told you roughly half of what you need to know.

Check which one a server listing refers to before you spend ten minutes wondering why an address will not resolve. If you and a friend cannot see each other's games, this is the first thing to check and it is right about ninety per cent of the time.

The four marines, and why you cannot all pick the gun

You take a squad of four into a mission. In a full game of four humans, each person controls one. With fewer people, the empty slots are filled by marines that follow you around and shoot things reasonably well without much judgement.

The classes matter more here than in most co-op shooters, because two of them own abilities the mission actually requires.

Tech is the one you cannot leave behind. Locked doors and computer terminals stand between you and the objective, and the tech marine is the one who opens them — through a small timing puzzle you play while everything in the level walks towards the noise you are making. A squad without a tech gets to a door and stops.

Medic carries healing. Damage in this game is not something you walk off between fights; it accumulates over a mission, and a squad with no medic finishes the second half of a level on a sliver of health, if it finishes at all.

Special weapons is the heavy firepower — the marine who deletes a corridor full of aliens and, on a bad day, also deletes two of you.

Officer is the support and leadership slot, buffing the people around them rather than putting out damage personally.

Sort this out in the lobby rather than in the level. The single most common way a group fails is four people picking whatever looked coolest and then discovering, at a sealed door, that nobody can open it.

Friendly fire is the mechanic, not a bug

This deserves its own heading because new players consistently assume something is broken.

Your bullets hit your teammates. So do your grenades, and so does fire. Set an incendiary off in a corridor and the flames sit there burning whatever walks through, which includes the marine sprinting back to you because something is chasing them. A minigun opening up down a hallway hits the swarm and the person standing between you and the swarm equally.

The design intent is obvious once you have played a mission: it forces the squad to spread out, to call out what they are doing, and to think about firing lines instead of everyone standing in one doorway holding the trigger. It also means the first hour is funny for everyone except the person who died.

Two habits fix most of it. Do not stand directly behind a teammate who is shooting. And say what you are about to throw before you throw it.

Installing it

Find it in the Steam store, add it to your account, and install it from the Library. The download is small by modern standards and the install goes where your Steam library lives, under steamapps/common with everything else.

Launch it once before you try to join anybody. First runs of Source games do setup work — shader caches, configuration files, the initial video settings pass — and a game that has never been started is a game that will make your friends wait while it does all of that.

While you are in the menus, find the option that enables the developer console. It sits in the options screens with the other advanced settings, and you want it on before you need it rather than while three people are waiting in a lobby.

Getting into a game

There are two routes, and they suit different situations.

Playing with people you know

Alien Swarm is built around a lobby. One person creates a game and the others join through Steam. Everyone picks a marine and a loadout, then the host starts the mission. For a group of four friends this is the entire process and you can ignore the rest of this section.

The host's machine runs the game, which means the host's connection is everyone else's connection. If one person in the group has a noticeably better upload and a wired connection, that person should host. This is not a small effect in a game where four people are shooting at the same swarm and the server is deciding who hit what.

Joining a listed server

The other route is a machine that stays on and keeps a game running whether or not you and your friends are awake. That is what dedicated servers are for, and it is what the server list collects. Every listing is queried directly rather than taken on trust, so the player count you see is measured.

To connect by address, open the developer console and type connect followed by a space and the full address, then press enter:

connect 203.0.113.10:27015

Two notes that apply to every Source game and catch people out on all of them. The port is part of the address — 27015 is the default, and a host running several servers on one machine has moved most of them somewhere else, so copy the whole address:port string rather than just the numbers before the colon. And the first connection to a server running custom content is slower than later ones, because the server is sending you files it needs you to have.

Steam's own server browser has a favourites tab that accepts an address typed in directly, without you having to find the server in a list first. For a game with a population this size, favouriting the two or three servers that have people on them at the hour you play is the difference between "there is nobody playing" and knowing exactly where to go.

What a mission actually asks of you

The campaign missions are objective runs through industrial interiors — power stations, tunnels, colony corridors — where the objective is a lever or a terminal and the difficulty is everything standing between you and it.

A few things structure every one of them.

Ammunition is finite. You do not regenerate ammunition and you do not find infinite crates. Emptying a magazine into a wall because something startled you has a cost later in the level. The squad that finishes a mission on hard difficulty is the squad that stopped shooting when there was nothing to shoot.

Doors are a tactic. The welder seals a door, and a sealed door buys time. Sealing the one behind you while the squad works on an objective is standard practice. Sealing the one in front of your teammate is the thing described at the top of this article.

Sentry guns hold a corridor. Deployed in the right place, one covers the direction nobody is watching. Deployed in the wrong place, it is a heavy object somebody carried across a level for nothing.

Fire is a wall. Incendiary weapons and grenades create burning ground that aliens will walk through and die in, which turns a corridor into a delay. It works on you identically.

Difficulty, and where to start

The game ships with escalating difficulty tiers, and the jump between them is real rather than cosmetic. On the lowest setting a competent group walks through the campaign. Two steps up, a single mistake at a chokepoint ends the mission for everybody.

Start lower than your pride suggests. The mechanics that matter — welding, hacking, ammunition discipline, not shooting your medic — are easier to learn when a mistake costs you thirty seconds instead of the run.

Public servers vary in what they are set to, and a server running a high difficulty with strangers is a specific experience. Quiet, tense, and liable to end without warning. Some people play it exclusively.

Problems you will hit

You cannot see your friend's game. Almost always the two-similar-games problem described above. Confirm you both launched the same Steam entry.

The game will not connect to a listed address. Check the port first. Then check the listing itself — if the hub shows it offline, the machine is down and nothing you do locally will change that.

Everything is dark and you cannot tell what is happening. The game is deliberately underlit and the camera angle hides a lot. Turn the brightness up in the video options. This is not cheating; it is what the option is for.

The lobby starts without a full squad. Empty slots are filled by marines under the game's own control. They are adequate rather than clever, and they will not open a door for you.

Where to go next

If the appeal here is four people co-operating against something that outnumbers them, the obvious neighbours are Left 4 Dead and Left 4 Dead 2, which run on the same engine family and use the same connect command in the same console. Killing Floor 2 and Natural Selection 2 sit nearby for the same reason.

If what you liked was the Source engine's community server culture rather than the top-down camera specifically, Team Fortress 2, Counter-Strike: Source and Garry's Mod all work the same way underneath, and everything in this guide about ports and slow first joins transfers directly.

And if you are trying to work out which of a handful of listings is worth your evening, what makes a server listing trustworthy is about exactly that problem.

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JoinGG is a live directory of community game servers. Every listing is queried directly every fifteen minutes, so the player count you see was measured rather than reported by its owner, and each one carries a copyable connect address. Alien Swarm servers are listed here, and every game on the site has its own hub. Player counts across every game are on the statistics page, and Alien Swarm's own numbers — servers online, players now, activity by hour — are on its statistics page.