If you're tired of your players constantly bumping into each other or getting stuck in doorways, you've probably realized that a roblox collisiongroup script is the way to go. It's one of those things that seems a bit intimidating when you first look at the API, but once you get the hang of it, you'll wonder how you ever managed without it. Basically, it's all about telling the game engine which objects should ignore each other and which ones should smack into each other.
Whether you're making a busy social hang-out where player-to-player collision is a nightmare, or a complex shooter where bullets need to pass through teammates but hit enemies, mastering this script is a total game-changer. Let's break down how to actually build one that doesn't break every time someone joins the server.
Why bother with collision groups anyway?
By default, Roblox wants everything to be solid. If a Part's CanCollide property is on, it hits everything else that has it on. That's fine for a simple hobby or a basic building game, but it gets messy fast in more "pro" projects. Think about a crowded lobby. If 50 players are all trying to run through a single door, it becomes a physics-induced mosh pit. Not exactly the "user experience" most devs are aiming for.
A roblox collisiongroup script lets you bypass that "everything hits everything" rule. You can create a group called "Players," another called "Projectiles," and maybe one called "IgnoreThese." Then, you just tell the PhysicsService: "Hey, make sure the Players group can't collide with itself, but let it collide with the environment." It's cleaner, more efficient, and way less glitchy than trying to toggle CanCollide manually on every single limb of a character every frame.
Setting up the PhysicsService basics
The brain behind all of this is PhysicsService. In the old days, we had to do a lot of manual heavy lifting, but now it's a bit more streamlined. Before you start assigning parts to groups, you actually have to register the groups themselves.
Usually, you'll want to do this in a Script (not a LocalScript) inside ServerScriptService. You want the server to be the source of truth for physics, or else you'll end up with some weird desync issues where a player thinks they're walking through a wall while the server thinks they're stuck.
```lua local PhysicsService = game:GetService("PhysicsService")
-- We create our groups here local groupName = "Players" PhysicsService:RegisterCollisionGroup(groupName)
-- Now we tell the game that players shouldn't hit other players PhysicsService:CollisionGroupSetCollidable(groupName, groupName, false) ```
It's pretty straightforward. You name the group, and then use CollisionGroupSetCollidable to define the interaction. The two names in the function are the groups you're comparing, and the boolean at the end (false) tells the game "don't let these two groups touch."
Making players walk through each other
The most common use for a roblox collisiongroup script is definitely disabling player-to-player collisions. To do this properly, you can't just set the group once; you need to make sure every single part of a player's character—the head, the torso, the legs—is assigned to that group the moment they spawn.
This is where people often get tripped up. Characters don't just "appear" fully formed in a single frame. You have to wait for them to load. Here's a reliable way to handle it:
```lua local PhysicsService = game:GetService("PhysicsService") local Players = game:GetService("Players")
local playerGroup = "Players" PhysicsService:RegisterCollisionGroup(playerGroup) PhysicsService:CollisionGroupSetCollidable(playerGroup, playerGroup, false)
local function setCollisionGroup(character) for _, part in ipairs(character:GetDescendants()) do if part:IsA("BasePart") then part.CollisionGroup = playerGroup end end end
Players.PlayerAdded:Connect(function(player) player.CharacterAdded:Connect(function(character) setCollisionGroup(character)
-- Sometimes accessories load a bit later, so we check again character.DescendantAdded:Connect(function(descendant) if descendant:IsA("BasePart") then descendant.CollisionGroup = playerGroup end end) end) end) ```
Using GetDescendants() is key here because characters are made of nested parts, folders, and models. If you only look at the top level, you'll miss half the limbs. I also added that DescendantAdded connection because Roblox sometimes drops hats or tools into the character a split second after the body loads. Without that extra check, your player's body might pass through others, but their giant oversized wings or sword might still go clunk.
Handling projectiles and specialized filters
Things get even more interesting when you start adding layers. Let's say you're building a dodgeball game. You want the ball to hit the floor and the players, but you might want the "ghosts" (players who are out) to be ignored by the ball entirely. Or maybe you want a "Team A" gate that "Team B" can't pass through.
You can set up multiple groups and define a whole matrix of rules. For example:
- Players (don't hit other Players)
- Projectiles (hit Players, hit Environment, but don't hit other Projectiles)
- GhostPlayers (don't hit Players, don't hit Projectiles)
In your roblox collisiongroup script, you'd just keep calling CollisionGroupSetCollidable to map out these relationships. It's like a "who's who" of physics. The beauty is that once a part is assigned to a group, you don't have to keep checking it. The engine handles the math for you, which is much better for your game's performance than running a bunch of Touched events or raycast filters manually.
Troubleshooting the common headaches
Even with a solid script, things can go sideways. One common issue is the "Default" group. Every single part in your game starts in the "Default" group. If you create a new group but forget to tell it how to interact with "Default," it might behave in ways you don't expect. Usually, new groups are set to collide with "Default" by default (redundant, I know), but it's always good to double-check.
Another thing to watch out for is Client vs Server. If you try to set a CollisionGroup in a LocalScript, it might look like it's working for that one player, but to everyone else on the server, that player is still bumping into things. Always try to handle the group assignment on the server unless you have a very specific reason not to (like some purely visual local effect).
Also, keep an eye on your group limits. Roblox used to have a very strict limit on how many collision groups you could have (it was 32 for a long time). They've since updated the system, but you still shouldn't go crazy. You don't need a unique group for every single item in your game. Group things by behavior, not by identity. All "Trees" can be in one group, all "Players" in another.
Optimizing for large games
If you're running a massive game with hundreds of moving parts, you want your roblox collisiongroup script to be as efficient as possible. Avoid looping through every part in the workspace to find things to group. Instead, use tags with CollectionService.
You can tag all your "Lava" parts with a tag called "LavaDamage," and then have a single script that finds everything with that tag and puts it into the "Hazard" collision group. This is way cleaner than having scripts sitting inside every single part of your map.
```lua local CollectionService = game:GetService("CollectionService") local PhysicsService = game:GetService("PhysicsService")
local hazardGroup = "Hazards" PhysicsService:RegisterCollisionGroup(hazardGroup)
local function handleHazard(part) if part:IsA("BasePart") then part.CollisionGroup = hazardGroup end end
-- Assign existing hazards for _, part in ipairs(CollectionService:GetTagged("LavaDamage")) do handleHazard(part) end
-- Listen for new hazards being added to the map dynamically CollectionService:GetInstanceAddedSignal("LavaDamage"):Connect(handleHazard) ```
This approach is basically the "pro" way to do it. It keeps your hierarchy clean and makes your physics logic centralized. If you decide later that you want the "Hazards" to stop hitting "Projectiles," you only have to change one line of code in one script, rather than hunting through dozens of different folders.
At the end of the day, a roblox collisiongroup script is just about organization. It's the difference between a game that feels clunky and "stock" and one that feels polished and intentional. Take the time to map out your physics groups on a piece of paper before you start coding—it'll save you a lot of "why is my player falling through the floor" debugging later on!