How to reduce lag in your Roblox game

"Laggy" is one of the most common words in bad Roblox reviews, and lag hits hardest on the cheap phones and old laptops many players use. The good news is that most lag comes from a handful of causes, and Roblox gives you the tools to find them. Measure first, then fix the biggest thing, then measure again.

Know which kind of lag you have

Players say "lag" for three different problems:

• Low frame rate (client lag): the game stutters or feels slow to render. Usually too much geometry, effects or client scripts.
• Server lag: everyone sees delays at once, actions take a moment to register, NPCs freeze. Usually heavy server scripts or physics.
• Network lag: the game renders smoothly but things jump around. Usually too much data sent between server and clients, or a player's poor connection.

Each has different fixes, so find out which one you have before changing anything.

Measure with Roblox's tools

• Developer Console (F9 in game): shows memory usage by category, server and client script activity, network traffic and errors. Check it in a live server, not just Studio.
• MicroProfiler (Ctrl+F6 on PC): shows exactly what each frame spends its time on. Look for tall spikes and what's inside them.
• Studio's device emulator: test on a simulated phone screen, but also test on a real low-end phone if you can. Emulation doesn't show real phone performance.
• Your own analytics: Creator Analytics can show performance metrics such as frame rate and crash rates by device. A drop after an update tells you what to look at.

Geometry and rendering

• Fewer, simpler parts. Thousands of small parts are expensive. Combine decorative detail into meshes, and reuse the same mesh where possible.
• Turn off what you don't need: CastShadow on small parts, CanCollide and CanTouch on decorations nobody touches, and CanQuery where raycasts don't need them.
• Use simpler collision fidelity (Box or Hull) for detailed decorative meshes.
• Limit particles, lights and transparent parts. Many overlapping transparent parts and lights with shadows are costly, especially on phones.
• Keep textures reasonable. Huge images for small objects waste memory.

Turn on StreamingEnabled

With StreamingEnabled, clients only load the parts of the world near them, which saves memory and load time on big maps. It changes how scripts work, because a LocalScript can't assume a distant part exists, so use WaitForChild with care and design around parts streaming in and out. For large maps it's usually the single biggest win for mobile players.

Scripts

• Don't run work every frame unless you must. Code connected to Heartbeat or RenderStepped runs dozens of times a second. If something only needs to happen every second, do it every second.
• Avoid tight loops like "while true do" with a very short wait doing heavy work.
• Disconnect events you no longer need, and destroy objects you're finished with, to avoid memory leaks that make long sessions slower and slower.
• Do visual effects on the client. The server should decide what happens; clients can draw the effects.
• Profile, don't guess. The script activity panel in the Developer Console shows which scripts use the most time.

Physics

• Anchor everything that doesn't need to move.
• Limit unanchored parts, such as tycoon drops or debris. Pool and reuse them, and remove them after a short time.
• Use fewer Humanoids for NPCs when you have many enemies; moving simple models along paths is far cheaper. How to make a tower defense game covers this approach.

Network traffic

• Send less, less often. Firing a RemoteEvent to every client every frame with lots of data floods connections. Send changes, not full state, and batch updates.
• Avoid replicating things clients don't need. Keep server-only objects in ServerStorage rather than the Workspace.
• Let clients predict. For things like cosmetic animations, tell clients once and let them play it locally.

Keep an eye on it after launch

Performance problems often arrive with updates: a new map, a new effect, a new pet with a particle trail. After each release, check the Developer Console in a busy live server and your analytics by device. If mobile session length drops after an update, lag is a likely suspect. Making your Roblox game mobile-friendly covers the rest of the phone experience.

Checklist

• Lag type identified: client, server or network
• Developer Console and MicroProfiler checked in a live server
• Tested on a real low-end phone
• Detail merged into meshes; shadows, collisions and queries off where unneeded
• StreamingEnabled for large maps, scripts adjusted for it
• Per-frame work minimised; events disconnected; effects on the client
• Unanchored parts limited; light-weight NPCs
• Remote traffic batched and reduced
• Performance checked after every update

When your game runs well, players stay longer, and session length is one of the signals Roblox uses in recommendations. See how the Roblox algorithm recommends games.