Building an Online Platform Game From Scratch
I spent about three weeks trying to get a multiplayer platformer to actually feel responsive over the network before I figured out what was going wrong. Most tutorials skip the stuff that makes these games frustrating to build. Here is what I learned. The core loop is straightforward. Each client predicts player movement locally, then sends position and input data to a server at a fixed tick rate, usually 30 or 60 times per second. The server validates that data, resolves collisions between players, and broadcasts the authoritative state back. Clients interpolate between received states so movement looks smooth instead of snapping around. The tricky part is latency. If two players are 100ms apart from the server, your character jumps on your screen but the server sees it 100ms later. A naive implementation makes everything feel laggy. You need client-side prediction and server reconciliation to mask that delay. Without it, the game is basically unplayable past about 80ms of round-trip time.
I used Node.js with UDP sockets for the networking layer instead of the more common TCP approach. TCP retransmits lost packets in order, which means if one packet drops, everything behind it waits. That causes stuttering that is immediately noticeable in a platformer where frame-perfect timing matters. UDP does not guarantee delivery, so I had to handle missing packets myself by using sequence numbers and dropping anything older than the current tick. This cut perceived latency by roughly half compared to a TCP-based setup I tried first.
Setting Up the Development Environment
You do not need a fancy engine. I used Unity for the client because its physics system handles platformer mechanics adequately, but the same approach works in Godot or even raw WebGL with a custom physics loop. For the server, I wrote everything in TypeScript running on Node.js, deployed through Docker containers on a VPS in the region closest to your player base. Start by defining your game tick rate. 30 ticks per second is the minimum that feels acceptable for a platformer. 60 is ideal if your target audience has good internet connections. Everything in the codebase should be synchronized to this tick, not to the rendering frame rate. Mixing tick-based logic with frame-based updates is the most common source of bugs in these projects. The player object needs a fixed set of properties transmitted every tick: position (x and y), velocity (vx and vy), ground state, and the input buffer from the last 4 ticks. That input buffer is critical for server reconciliation. When the server receives a client state that conflicts with its own calculation, it replays those buffered inputs forward to find where things diverged.
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Handling Collision and Physics
Platformer physics have a specific set of requirements that general-purpose physics engines do not always handle well. You need Coyote Time, which is a brief window after leaving a platform edge where the player can still jump. Without it, players miss jumps about 30% of the time on mediocre connections and blame the game design rather than the network code. I also added Jump Buffering. If a player presses jump 80ms before landing, the game queues that input and executes it the moment the player touches solid ground. Both features are simple to implement but completely change the feel. Skipping them because they seem trivial is a mistake I see repeatedly in early builds. Server-side collision detection needs to run independently of the client. Never trust client-reported positions for collision resolution. Clients can report they are on the ground when they are actually in mid-air due to prediction errors. The server checks AABB overlap against all platforms and other players every tick, then corrects the position if needed before broadcasting the authoritative state.
Common Pitfalls and Why They Matter
The biggest mistake I made early on was updating the render directly from the network tick. Games run at 60fps or higher, and the network runs at 30 or 60 ticks. These are not the same loop. When you couple them, your rendering either chokes the network thread or vice versa, and you get inconsistent frame times that feel jittery even if the average fps looks fine on paper. Instead, run the game logic and networking on their own threads or update loops, and let the render loop interpolate between the last two received server states. The interpolation factor goes from 0 to 1 between ticks, smoothly sliding the player model into place. This is what makes online platformers feel fluid rather than choppy. Another issue I ran into was the bandwidth explosion when players start interacting with each other frequently. In a sparse platformer with few players, the data payload is manageable. Once you add 16 players on the same map, each sending position, velocity, and input every tick, you are pushing several kilobytes per second per player. For a tournament or competitive mode, this adds up fast and can overwhelm residential internet connections on both upload and download ends.
The workaround I settled on was State Interpolation with Delta Compression. Instead of sending full positions every tick, I only sent changes from the previous state plus a timestamp. If a player was standing still, the delta was zero and the server skipped the send entirely. This reduced my bandwidth usage by about 70% in scenarios where players were not constantly moving. It also meant I could support more concurrent players on the same server hardware without upgrading the infrastructure.
Where This Approach Breaks Down
The UDP + delta compression setup works well for 2 to 16 players on a single server. Beyond that, you hit diminishing returns. The server's validation loop becomes a bottleneck because every collision check, every position reconciliation, and every state broadcast happens sequentially in a single process. If you need more than 16 simultaneous players in the same space, you should split the map into shards and route each shard to its own server instance, then synchronize between them. That adds significant complexity and is probably unnecessary unless you are building something on a larger scale. There is also the matter of cheating. Client-side prediction means the client decides what to display, and there is always a small window where a determined player can manipulate input timing to gain an advantage. Full lockstep or frame-by-frame verification would eliminate this but increases latency to unacceptable levels for a fast-paced platformer. The compromise is to validate critical events server-side, like damage calculations and score events, while allowing movement to remain mostly client-authoritative with periodic reconciliation checks.
Practical Steps to Get Started
Begin with a single-player prototype that has the core platformer mechanics working. Get jumping, running, and collision feeling right before touching any networking code. Then add one other player as a simulated bot. The bot sends fake network packets at the same interval you plan to use for real players, so you can test the receive and render pipeline without dealing with actual network variables. Once the bot behaves correctly, replace it with a real second client on the same machine. Loopback networking introduces near-zero latency, which hides many bugs that only appear under real-world conditions. After that works, deploy the server to a machine in a different location and test again. The difference in feel will show you exactly how much prediction and reconciliation you need to tune. The online platform game development space has enough scattered documentation that piecing together a working system takes considerable time. The fundamentals are well understood, but the edge cases—like the coyote time interaction with server-side lag compensation or the exact timing of delta compression resets—are rarely explained in any single place. Learning them through trial and error is unavoidable, but being aware of the common failure points upfront saves weeks of debugging.
