How to Make a Platformer Game in the Browser
The platformer is the classic rite of passage in game development, and for good reason. It contains a complete set of fundamental systems, real-time movement, collision, camera, level design, and enemies, in a package small enough for one person to finish, and it teaches game feel more directly than any other genre. The difference between a platformer that feels sluggish and one that feels alive comes down to a handful of details in how the jump works, which makes it the perfect project for learning what separates a tech demo from a real game. This guide walks through building one from an empty editor to a playable level.
Step 1: Choose an Engine and Get the Loop Running
Start with a 2D framework rather than raw canvas, because a platformer needs sprites, input, and a game loop that a framework gives you for free. Phaser is the natural choice for a web platformer: it ships with arcade physics, tilemap support, sprite animation, and input handling, which are precisely the systems this genre needs. If you prefer to architect the systems yourself for maximum control, PixiJS gives you a blazing-fast renderer and you supply the game logic on top. Either way, your first milestone is a character sprite on screen that moves left and right with the arrow or WASD keys, driven by a game loop that updates and renders every frame.
At this stage, keep the physics simple. Apply a horizontal velocity when a movement key is held, apply gravity as a constant downward acceleration every frame, and integrate velocity into position. You will not have collision yet, so the character will fall through the floor, which is fine. The goal of this step is a running loop, working input, and gravity, the skeleton that everything else hangs on.
Step 2: Build Tile-Based Collision
Platformer levels are almost always built from tiles, a grid of square cells where some are solid ground and walls and others are empty air. This representation is efficient, easy to design with a tilemap editor, and simple to collide against. The collision routine checks the player's bounding box against the solid tiles it overlaps and pushes the player out so it rests on surfaces instead of passing through them. The single most important technique here is to resolve collision one axis at a time: move the player horizontally and resolve horizontal overlaps, then move vertically and resolve vertical overlaps. Resolving both at once produces corner bugs where the player sticks or jitters, and the per-axis approach eliminates them.
Per-axis resolution also gives you the information the rest of the game needs. When you resolve the vertical axis and find the player was pushed up out of a tile, you know the player is standing on ground, which sets the grounded flag that the jump depends on. When the player was pushed down, you know they hit their head on a ceiling and should cancel upward velocity. This grounded state is the hinge between collision and the jump, so build it carefully here.
Step 3: Make the Jump Feel Good
This is the step that separates a platformer that feels great from one that feels broken, and it is almost entirely about forgiveness and control. Three techniques do most of the work. Variable jump height lets the player control how high they jump by holding the button longer: cut the upward velocity short when the button is released early, so a tap is a small hop and a hold is a full leap. Coyote time gives the player a few frames after walking off a ledge during which a jump still counts, which matches what players expect and removes the maddening feeling of pressing jump just too late. Jump buffering remembers a jump pressed a few frames before landing and executes it the instant the player touches ground, so an early press is never swallowed.
None of these is hard to code, each is a few lines and a timer, but together they transform the feel of the game. Players cannot usually name these techniques, but they feel their absence as the game being stiff or unfair. Tune the numbers by playing constantly: adjust gravity, jump velocity, the coyote window, and the buffer window until the character feels responsive and grounded. This tuning is the real work of a platformer, and it is worth spending more time here than anywhere else.
Step 4: Add a Follow Camera and Design Levels
Once the character moves well, the world needs to be bigger than the screen, which means a camera that follows the player. A good follow camera does not lock rigidly to the player but eases toward them with a slight lag and often looks ahead in the direction of movement, which keeps the view comfortable and shows the player what is coming. Add bounds so the camera stops at the edges of the level rather than showing empty space beyond it. Most frameworks, Phaser included, provide a camera that follows a sprite with configurable smoothing, so this is mostly configuration rather than new code.
With a camera in place, design levels that teach. The opening of a platformer should introduce each mechanic in a safe space before testing it under pressure: show the player a jump they cannot fail, then a jump with a pit, then a jump with a pit and an enemy. This teach-then-test rhythm is the craft of platformer level design, and it is what makes a game feel fair and well-paced. Build levels in a tilemap editor like Tiled and load them as data, which keeps level content out of code and lets you iterate quickly.
Step 5: Add Enemies, Hazards, and a Goal
Movement and levels make a playground, but a game needs challenge and a goal. Start with the simplest enemies: a walker that paces back and forth on a platform and hurts the player on contact, defeated by being jumped on. This single enemy type, combined with hazards like spikes and pits, is enough to make levels meaningful. Add collectibles such as coins to reward exploration and a clear level-end goal like a flag or door that loads the next level. With a fail state from enemies and hazards and a win state from reaching the goal, the playground becomes a game.
From here, depth comes from variety within the systems you have built: enemies with different movement patterns, moving platforms, one-way platforms, and mechanics like wall jumps or dashes that extend the movement vocabulary. Each addition reuses the collision and feel work you already did, which is why the second half of a platformer goes faster than the first. Polish with sound effects for jumping, landing, and collecting, and a few particles, because that feedback is a large part of why good platformers feel satisfying.
The platformer lives or dies on the jump. Resolve tile collision per axis to get a reliable grounded state, then spend most of your time on variable jump height, coyote time, and jump buffering, because that forgiveness is what makes the genre feel good.
Where AI Helps in a Platformer
A platformer is a systems-bottlenecked genre, so AI helps most as a coding assistant rather than a content generator. An AI assistant is excellent at scaffolding the collision routine, explaining why per-axis resolution works, and generating the timer logic for coyote time and jump buffering, which lets you move quickly through the engineering. Where generative AI does help with content is art: AI sprite generators can produce a character sheet, tilesets, and enemy sprites far faster than drawing them by hand, which removes the one content bottleneck the genre has. Use AI to write the systems and to fill the art pipeline, but expect to do the feel tuning yourself, because that is a matter of playing and adjusting that no tool can fully automate.