diff --git a/.gitignore b/.gitignore
index d163863..9e857c8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,3 @@
-build/
\ No newline at end of file
+build/
+world.json
+world.json.tmp
diff --git a/client/blocks/dirt.ts b/client/blocks/dirt.ts
index 75938ab..7a61e3e 100644
--- a/client/blocks/dirt.ts
+++ b/client/blocks/dirt.ts
@@ -17,6 +17,7 @@ const block = EverythingRegistry.register<BlockRegistry>("blocks", "bworld:dirt"
 		const maybe_item = player_inventory.container.get_item(player_inventory.hotbar_selected);
 		if (maybe_item && maybe_item.type_id === "bworld:hoe") {
 			dimension.add_block({ x: block.x, y: block.y, z: block.z, id: "bworld:hoed_dirt" });
+			dimension.sync_block(block.x, block.y, block.z);
 			return true;
 		}
 		return false;
diff --git a/client/blocks/grass.ts b/client/blocks/grass.ts
index 158c5e7..20b0b7c 100644
--- a/client/blocks/grass.ts
+++ b/client/blocks/grass.ts
@@ -17,6 +17,7 @@ EverythingRegistry.register<BlockRegistry>("blocks", "bworld:grass", {
 		if (item?.type_id === "bworld:hoe") {
 			block.id = "bworld:hoed_dirt";
 			dimension.add_block(block);
+			dimension.sync_block(block.x, block.y, block.z);
 			return true;
 		}
 		return false;
diff --git a/client/client_world.ts b/client/client_world.ts
index 7841217..c201129 100644
--- a/client/client_world.ts
+++ b/client/client_world.ts
@@ -13,6 +13,13 @@ import { Dimension } from "./components/dimension.ts";
 import { GuiRenderSystem, GuiTickSystem } from "./gui/gui_systems.ts";
 import { WorldGenerationSystem } from "./systems/world_generation_system.ts";
 import { CollisionSystem } from "./systems/collision_system.ts";
+import { NetworkSystem } from "./systems/network_system.ts";
+import { Connection } from "./network.ts";
+
+export interface ChatLine {
+	text: string;
+	time: number;
+}
 
 export class ClientWorld extends World {
 	paused = false;
@@ -20,8 +27,13 @@ export class ClientWorld extends World {
 
 	dimension!: Dimension;
 
-	constructor() {
+	// undefined when playing single player
+	connection?: Connection;
+	chat_log: ChatLine[] = [];
+
+	constructor(connection?: Connection) {
 		super("game");
+		this.connection = connection;
 
 		this.add_state("main_menu");
 		this.add_state("paused");
@@ -39,6 +51,7 @@ export class ClientWorld extends World {
 		// Logic systems
 		this.add_system(new UIInteractionSystem(), "main_menu");
 		this.add_system(new UIInteractionSystem(), "paused");
+		this.add_system(new NetworkSystem(), "game");
 		this.add_system(new GuiTickSystem(), "game");
 		this.add_system(new PlayerControlsSystem(), "game");
 		this.add_system(new WorldGenerationSystem(), "game");
@@ -53,4 +66,11 @@ export class ClientWorld extends World {
 		this.add_system(new UIRenderSystem(), "main_menu");
 		this.add_system(new UIRenderSystem(), "paused");
 	}
+
+	add_chat(text: string) {
+		this.chat_log.push({ text, time: performance.now() });
+		if (this.chat_log.length > 100) {
+			this.chat_log.shift();
+		}
+	}
 }
diff --git a/client/components/dimension.ts b/client/components/dimension.ts
index 07cf1bb..57bf093 100644
--- a/client/components/dimension.ts
+++ b/client/components/dimension.ts
@@ -1,6 +1,7 @@
 import { Component } from "$/common/ecs/mod.ts";
+import { AIR_ID, BlockChange } from "$/common/protocol.ts";
 import { BlockRegistry, EverythingRegistry } from "$/common/everything_registry.ts";
-import { AIR, Faces, ID_MASK, VOID } from "../../common/constants.ts";
+import { AIR, CHUNK_AREA, CHUNK_HEIGHT, CHUNK_SIZE, Faces, ID_MASK, VOID } from "../../common/constants.ts";
 import { AssetManager } from "../assets.ts";
 import { ClientWorld } from "../client_world.ts";
 import { generate_chunk } from "../generation.ts";
@@ -24,9 +25,7 @@ export interface Block {
 	z: number;
 }
 
-export const CHUNK_SIZE = 16;
-export const CHUNK_HEIGHT = 128;
-export const CHUNK_AREA = CHUNK_SIZE * CHUNK_SIZE;
+export { CHUNK_AREA, CHUNK_HEIGHT, CHUNK_SIZE };
 
 export interface Chunk {
 	x: number;
@@ -47,10 +46,15 @@ export class Dimension extends Component {
 	chunks: Chunk[] = [];
 	second_timer = 0;
 	tick_timer = 0;
+	seed: string;
 
-	constructor(world: ClientWorld) {
+	// blocks players changed from the generated terrain, per chunk, so they survive reloading chunks
+	changes = new Map<string, Map<string, BlockChange>>();
+
+	constructor(world: ClientWorld, seed = "seed") {
 		super();
 		this.world = world;
+		this.seed = seed;
 	}
 
 	add_chunk(x: number, z: number) {
@@ -200,8 +204,57 @@ export class Dimension extends Component {
 		return [x, y, z];
 	}
 
+	record_change(x: number, y: number, z: number, id: string) {
+		const chunk_key = `${Math.floor(x / CHUNK_SIZE)},${Math.floor(z / CHUNK_SIZE)}`;
+		let chunk_changes = this.changes.get(chunk_key);
+		if (!chunk_changes) {
+			chunk_changes = new Map();
+			this.changes.set(chunk_key, chunk_changes);
+		}
+		chunk_changes.set(`${x},${y},${z}`, [x, y, z, id]);
+	}
+
+	// call after the player changes a block so it gets saved and sent to the server
+	sync_block(x: number, y: number, z: number) {
+		const numeric_id = this.get_block(x, y, z);
+		const id = numeric_id === AIR ? AIR_ID : EverythingRegistry.get_by_id<BlockRegistry>("blocks", numeric_id)?.id;
+		if (!id) {
+			return;
+		}
+		this.record_change(x, y, z, id);
+		this.world.connection?.send({ type: "set_block", x, y, z, id });
+	}
+
+	// set a block without drops or syncing, for changes that came from somewhere else
+	apply_change(x: number, y: number, z: number, id: string) {
+		const chunk = this.get_chunk(Math.floor(x / CHUNK_SIZE), Math.floor(z / CHUNK_SIZE));
+		if (!chunk || !chunk.generated) {
+			return;
+		}
+
+		const current = this.get_block(x, y, z);
+		if (id === AIR_ID) {
+			if (current !== AIR) {
+				this.break_block(x, y, z, false);
+			}
+			return;
+		}
+
+		const nid = EverythingRegistry.get_id("blocks", id);
+		if (nid === undefined || nid === current) {
+			return;
+		}
+		this.add_block({ x, y, z, id });
+	}
+
+	apply_chunk_changes(cx: number, cz: number) {
+		for (const [x, y, z, id] of this.changes.get(`${cx},${cz}`)?.values() ?? []) {
+			this.apply_change(x, y, z, id);
+		}
+	}
+
 	load_chunk(cx: number, cz: number) {
-		generate_chunk(this, cx, cz);
+		generate_chunk(this, cx, cz, this.seed);
 		const chunk = this.get_chunk(cx, cz);
 		if (chunk) {
 			chunk.generated = true;
@@ -221,6 +274,13 @@ export class Dimension extends Component {
 				neighbor.dirty = true;
 			}
 		}
+
+		// trees spill into neighboring chunks, so their changes need reapplying too
+		for (let dx = -1; dx <= 1; dx++) {
+			for (let dz = -1; dz <= 1; dz++) {
+				this.apply_chunk_changes(cx + dx, cz + dz);
+			}
+		}
 	}
 
 	unload_chunk(cx: number, cz: number) {
diff --git a/client/game.ts b/client/game.ts
index ff09e3d..91e7de5 100644
--- a/client/game.ts
+++ b/client/game.ts
@@ -12,7 +12,10 @@ export function start_game(world: ClientWorld) {
 	world.clear_entities();
 
 	const dimension = new Entity("dimension");
-	world.dimension = new Dimension(world);
+	world.dimension = new Dimension(world, world.connection?.seed);
+	for (const [x, y, z, id] of world.connection?.initial_changes ?? []) {
+		world.dimension.record_change(x, y, z, id);
+	}
 	dimension.add(world.dimension);
 	world.add_entity(dimension);
 
diff --git a/client/generation.ts b/client/generation.ts
index 04f0ec5..5f0f71b 100644
--- a/client/generation.ts
+++ b/client/generation.ts
@@ -129,8 +129,8 @@ function can_place_tree(tree_map: boolean[][], local_x: number, local_z: number)
 	return true;
 }
 
-function place_tree(dimension: Dimension, x: number, y: number, z: number, biome: Biome) {
-	const height = Math.floor(Math.random() * 3) + (biome === "jungle" ? 8 : 4);
+function place_tree(dimension: Dimension, rng: Alea, x: number, y: number, z: number, biome: Biome) {
+	const height = Math.floor(rng.next() * 3) + (biome === "jungle" ? 8 : 4);
 	const trunk_block = "bworld:log";
 	const leaves_block = "bworld:leaves";
 
@@ -177,6 +177,8 @@ export function generate_chunk(dimension: Dimension, cx: number, cz: number, see
 	const moisture_noise = create_noise_2d(new Alea(seed + "_moisture"));
 	const feature_noise = create_noise_2d(new Alea(seed + "_feature"));
 	const ore_noises = ORES.map((ore) => create_noise_3d(new Alea(seed + "_" + ore.id)));
+	// seeded per chunk so every client generates the exact same terrain
+	const rng = new Alea(`${seed}_chunk_${cx}_${cz}`);
 
 	const biome_scale = 0.003;
 	const terrain_scale = 0.01;
@@ -226,7 +228,7 @@ export function generate_chunk(dimension: Dimension, cx: number, cz: number, see
 					block = "bworld:dirt";
 				}
 
-				if (biome === "swamp" && y === height && Math.random() < 0.2) {
+				if (biome === "swamp" && y === height && rng.next() < 0.2) {
 					block = "bworld:water";
 				}
 
@@ -234,7 +236,7 @@ export function generate_chunk(dimension: Dimension, cx: number, cz: number, see
 			}
 
 			if (should_place_tree(feature_noise, biome, wx, wz) && can_place_tree(tree_map, x, z)) {
-				place_tree(dimension, wx, height + 1, wz, biome);
+				place_tree(dimension, rng, wx, height + 1, wz, biome);
 				tree_map[x][z] = true;
 			}
 		}
diff --git a/client/gui/gui_chat.ts b/client/gui/gui_chat.ts
index dd5f1dd..b52c84b 100644
--- a/client/gui/gui_chat.ts
+++ b/client/gui/gui_chat.ts
@@ -4,6 +4,8 @@ import { InputManager } from "../input_manager.ts";
 import { ClientWorld } from "../client_world.ts";
 import { PlayerComponent } from "../player.ts";
 import { ItemStack } from "../inventory.ts";
+import { MAX_CHAT_LENGTH } from "$/common/protocol.ts";
+import { render_chat_log } from "../systems/rendering/network.ts";
 
 export class GuiChat extends GuiScreen {
 	world: ClientWorld;
@@ -22,6 +24,7 @@ export class GuiChat extends GuiScreen {
 		draw_rect(0, 0, canvas.width, canvas.height, [0, 0, 0, 0.8]);
 
 		const y = canvas.height - 32;
+		render_chat_log(this.world, true, y - 8);
 		draw_rect(0, y, canvas.width, canvas.height, [0, 0, 0, 0.4]);
 
 		draw_text(this.text_typed, 0, y, 2, [1, 1, 1]);
@@ -85,6 +88,9 @@ export class GuiChat extends GuiScreen {
 		const typed = InputManager.get_typed_characters();
 
 		for (const char of typed) {
+			if (this.text_typed.length >= MAX_CHAT_LENGTH) {
+				break;
+			}
 			this.text_typed = this.text_typed.slice(0, this.caret) + char + this.text_typed.slice(this.caret);
 			this.caret += 1;
 		}
@@ -98,8 +104,12 @@ export class GuiChat extends GuiScreen {
 	submit() {
 		if (this.text_typed.startsWith("/")) {
 			this.command();
-		} else {
-			// we dont have multiplayer lol?
+		} else if (this.text_typed.trim().length > 0) {
+			if (this.world.connection) {
+				this.world.connection.send({ type: "chat", text: this.text_typed });
+			} else {
+				this.world.add_chat(this.text_typed);
+			}
 		}
 		this.text_typed = "";
 
diff --git a/client/main.ts b/client/main.ts
index 3a3d5aa..a519611 100644
--- a/client/main.ts
+++ b/client/main.ts
@@ -1,6 +1,7 @@
 import { AssetManager } from "./assets.ts";
 import { ClientWorld } from "./client_world.ts";
 import { InputManager } from "./input_manager.ts";
+import { Connection, get_player_name, get_server_url } from "./network.ts";
 import { begin_drawing, clear_background, end_drawing, init_font, init_window } from "./renderer/mod.ts";
 
 await import("./blocks/mod.ts");
@@ -90,7 +91,15 @@ await AssetManager.instance.load_all();
 
 init_font();
 
-const client_world = new ClientWorld();
+const connection = await Connection.open(get_server_url(), get_player_name());
+if (connection) {
+	console.log(`Connected to ${get_server_url()}`);
+} else {
+	console.log("Couldn't reach a server, playing single player");
+}
+
+const client_world = new ClientWorld(connection);
+client_world.add_chat(connection ? "Connected to the server" : "Playing single player");
 
 const loop = new ClientLoop(client_world);
 loop.start();
diff --git a/client/network.ts b/client/network.ts
new file mode 100644
index 0000000..eed4e52
--- /dev/null
+++ b/client/network.ts
@@ -0,0 +1,125 @@
+import { BlockChange, ClientMessage, PlayerInfo, ServerMessage } from "$/common/protocol.ts";
+
+const CONNECT_TIMEOUT_MS = 3000;
+
+export interface RemotePlayer extends PlayerInfo {
+	// where we draw them, eased towards x/y/z so movement isnt choppy
+	display_x: number;
+	display_y: number;
+	display_z: number;
+	color: [number, number, number];
+}
+
+export class Connection {
+	socket: WebSocket;
+	id: string;
+	seed: string;
+	initial_changes: BlockChange[];
+	players = new Map<string, RemotePlayer>();
+
+	// handled by the network system inside the game loop, not whenever the socket feels like it
+	incoming: ServerMessage[] = [];
+	closed = false;
+
+	constructor(socket: WebSocket, id: string, seed: string, players: PlayerInfo[], changes: BlockChange[]) {
+		this.socket = socket;
+		this.id = id;
+		this.seed = seed;
+		this.initial_changes = changes;
+		for (const player of players) {
+			this.add_player(player);
+		}
+
+		socket.addEventListener("message", (event) => {
+			this.incoming.push(JSON.parse(event.data));
+		});
+		socket.addEventListener("close", () => {
+			this.closed = true;
+		});
+	}
+
+	send(message: ClientMessage) {
+		if (this.socket.readyState === WebSocket.OPEN) {
+			this.socket.send(JSON.stringify(message));
+		}
+	}
+
+	add_player(player: PlayerInfo) {
+		this.players.set(player.id, {
+			...player,
+			display_x: player.x,
+			display_y: player.y,
+			display_z: player.z,
+			color: color_from_name(player.name),
+		});
+	}
+
+	static open(url: string, name: string): Promise<Connection | undefined> {
+		return new Promise((resolve) => {
+			let socket: WebSocket;
+			try {
+				socket = new WebSocket(url);
+			} catch {
+				resolve(undefined);
+				return;
+			}
+
+			const timeout = setTimeout(() => {
+				socket.close();
+				resolve(undefined);
+			}, CONNECT_TIMEOUT_MS);
+
+			socket.addEventListener("open", () => {
+				socket.send(JSON.stringify({ type: "hello", name } satisfies ClientMessage));
+			});
+
+			socket.addEventListener("message", (event) => {
+				const message: ServerMessage = JSON.parse(event.data);
+				if (message.type === "welcome") {
+					clearTimeout(timeout);
+					resolve(new Connection(socket, message.id, message.seed, message.players, message.changes));
+				}
+			}, { once: true });
+
+			socket.addEventListener("error", () => {
+				clearTimeout(timeout);
+				resolve(undefined);
+			});
+		});
+	}
+}
+
+function color_from_name(name: string): [number, number, number] {
+	let hash = 0;
+	for (const ch of name) {
+		hash = (hash * 31 + ch.charCodeAt(0)) | 0;
+	}
+	const hue = ((hash % 360) + 360) % 360;
+	// hsl with s=0.6 l=0.6 to rgb
+	const c = 0.48;
+	const x = c * (1 - Math.abs(((hue / 60) % 2) - 1));
+	const m = 0.36;
+	const [r, g, b] = hue < 60
+		? [c, x, 0]
+		: hue < 120
+		? [x, c, 0]
+		: hue < 180
+		? [0, c, x]
+		: hue < 240
+		? [0, x, c]
+		: hue < 300
+		? [x, 0, c]
+		: [c, 0, x];
+	return [r + m, g + m, b + m];
+}
+
+export function get_server_url(): string {
+	const params = new URLSearchParams(location.search);
+	const server = params.get("server");
+	const protocol = location.protocol === "https:" ? "wss:" : "ws:";
+	return `${protocol}//${server ?? location.host}/ws`;
+}
+
+export function get_player_name(): string {
+	return new URLSearchParams(location.search).get("name") ?? "";
+}
diff --git a/client/renderer/models.ts b/client/renderer/models.ts
index ed5f647..9b17faa 100644
--- a/client/renderer/models.ts
+++ b/client/renderer/models.ts
@@ -191,3 +191,69 @@ export function push_bottom_face(
 	push_vertex(x2, y, z2, u1, v0, r, g, b, a);
 	push_vertex(x, y, z2, u0, v0, r, g, b, a);
 }
+
+// solid colored box, draw it with white_tex as the current texture
+export function push_box(
+	x: number,
+	y: number,
+	z: number,
+	width: number,
+	height: number,
+	depth: number,
+	r = 1,
+	g = 1,
+	b = 1,
+	a = 1,
+) {
+	const x2 = x + width;
+	const y2 = y + height;
+	const z2 = z + depth;
+
+	// front
+	push_vertex(x, y, z2, 0, 1, r, g, b, a);
+	push_vertex(x2, y, z2, 1, 1, r, g, b, a);
+	push_vertex(x2, y2, z2, 1, 0, r, g, b, a);
+	push_vertex(x, y, z2, 0, 1, r, g, b, a);
+	push_vertex(x2, y2, z2, 1, 0, r, g, b, a);
+	push_vertex(x, y2, z2, 0, 0, r, g, b, a);
+
+	// back
+	push_vertex(x2, y, z, 0, 1, r * 0.8, g * 0.8, b * 0.8, a);
+	push_vertex(x, y, z, 1, 1, r * 0.8, g * 0.8, b * 0.8, a);
+	push_vertex(x, y2, z, 1, 0, r * 0.8, g * 0.8, b * 0.8, a);
+	push_vertex(x2, y, z, 0, 1, r * 0.8, g * 0.8, b * 0.8, a);
+	push_vertex(x, y2, z, 1, 0, r * 0.8, g * 0.8, b * 0.8, a);
+	push_vertex(x2, y2, z, 0, 0, r * 0.8, g * 0.8, b * 0.8, a);
+
+	// left
+	push_vertex(x, y, z, 0, 1, r * 0.9, g * 0.9, b * 0.9, a);
+	push_vertex(x, y, z2, 1, 1, r * 0.9, g * 0.9, b * 0.9, a);
+	push_vertex(x, y2, z2, 1, 0, r * 0.9, g * 0.9, b * 0.9, a);
+	push_vertex(x, y, z, 0, 1, r * 0.9, g * 0.9, b * 0.9, a);
+	push_vertex(x, y2, z2, 1, 0, r * 0.9, g * 0.9, b * 0.9, a);
+	push_vertex(x, y2, z, 0, 0, r * 0.9, g * 0.9, b * 0.9, a);
+
+	// right
+	push_vertex(x2, y, z2, 0, 1, r * 0.9, g * 0.9, b * 0.9, a);
+	push_vertex(x2, y, z, 1, 1, r * 0.9, g * 0.9, b * 0.9, a);
+	push_vertex(x2, y2, z, 1, 0, r * 0.9, g * 0.9, b * 0.9, a);
+	push_vertex(x2, y, z2, 0, 1, r * 0.9, g * 0.9, b * 0.9, a);
+	push_vertex(x2, y2, z, 1, 0, r * 0.9, g * 0.9, b * 0.9, a);
+	push_vertex(x2, y2, z2, 0, 0, r * 0.9, g * 0.9, b * 0.9, a);
+
+	// top
+	push_vertex(x, y2, z2, 0, 1, r, g, b, a);
+	push_vertex(x2, y2, z2, 1, 1, r, g, b, a);
+	push_vertex(x2, y2, z, 1, 0, r, g, b, a);
+	push_vertex(x, y2, z2, 0, 1, r, g, b, a);
+	push_vertex(x2, y2, z, 1, 0, r, g, b, a);
+	push_vertex(x, y2, z, 0, 0, r, g, b, a);
+
+	// bottom
+	push_vertex(x, y, z, 0, 1, r * 0.6, g * 0.6, b * 0.6, a);
+	push_vertex(x2, y, z, 1, 1, r * 0.6, g * 0.6, b * 0.6, a);
+	push_vertex(x2, y, z2, 1, 0, r * 0.6, g * 0.6, b * 0.6, a);
+	push_vertex(x, y, z, 0, 1, r * 0.6, g * 0.6, b * 0.6, a);
+	push_vertex(x2, y, z2, 1, 0, r * 0.6, g * 0.6, b * 0.6, a);
+	push_vertex(x, y, z2, 0, 0, r * 0.6, g * 0.6, b * 0.6, a);
+}
diff --git a/client/systems/network_system.ts b/client/systems/network_system.ts
new file mode 100644
index 0000000..90a5dff
--- /dev/null
+++ b/client/systems/network_system.ts
@@ -0,0 +1,77 @@
+import { System } from "$/common/ecs/mod.ts";
+import { Position } from "$/common/components/position.ts";
+import { ClientWorld } from "../client_world.ts";
+import { Camera } from "../components/camera.ts";
+
+const MOVE_SEND_INTERVAL = 1 / 10;
+const REMOTE_PLAYER_SMOOTHING = 12;
+
+export class NetworkSystem extends System {
+	move_timer = 0;
+
+	update(world: ClientWorld, delta: number): void {
+		const connection = world.connection;
+		if (!connection) {
+			return;
+		}
+
+		for (const message of connection.incoming) {
+			switch (message.type) {
+				case "player_join":
+					connection.add_player(message.player);
+					break;
+				case "player_leave":
+					connection.players.delete(message.id);
+					break;
+				case "player_move": {
+					const player = connection.players.get(message.id);
+					if (player) {
+						player.x = message.x;
+						player.y = message.y;
+						player.z = message.z;
+						player.yaw = message.yaw;
+						player.pitch = message.pitch;
+					}
+					break;
+				}
+				case "set_block":
+					world.dimension.record_change(message.x, message.y, message.z, message.id);
+					world.dimension.apply_change(message.x, message.y, message.z, message.id);
+					break;
+				case "chat":
+					world.add_chat(message.from ? `<${message.from}> ${message.text}` : message.text);
+					break;
+			}
+		}
+		connection.incoming.length = 0;
+
+		if (connection.closed) {
+			world.add_chat("Lost connection to the server");
+			world.connection = undefined;
+			return;
+		}
+
+		const t = Math.min(1, delta * REMOTE_PLAYER_SMOOTHING);
+		for (const player of connection.players.values()) {
+			player.display_x += (player.x - player.display_x) * t;
+			player.display_y += (player.y - player.display_y) * t;
+			player.display_z += (player.z - player.display_z) * t;
+		}
+
+		this.move_timer += delta;
+		if (this.move_timer >= MOVE_SEND_INTERVAL) {
+			this.move_timer = 0;
+			const [player] = world.get_tag("player")!;
+			const position = player.get(Position)!;
+			const camera = player.get(Camera)!;
+			connection.send({
+				type: "move",
+				x: position.x,
+				y: position.y,
+				z: position.z,
+				yaw: camera.yaw,
+				pitch: camera.pitch,
+			});
+		}
+	}
+}
diff --git a/client/systems/player_controls.ts b/client/systems/player_controls.ts
index 5fc6469..d69d14a 100644
--- a/client/systems/player_controls.ts
+++ b/client/systems/player_controls.ts
@@ -138,6 +138,7 @@ export class PlayerControlsSystem extends System {
 					const drop_item = !block_info.requires_tool ||
 						holding_item_info?.tool_type === block_info.tool_to_break;
 					world.dimension.break_block(block.x, block.y, block.z, drop_item);
+					world.dimension.sync_block(block.x, block.y, block.z);
 					player_component.break_progress_max = 0;
 					player_component.break_progress = 0;
 				}
@@ -171,6 +172,7 @@ export class PlayerControlsSystem extends System {
 								z: block.z + offset.z,
 								id: item_info.block_id,
 							});
+							world.dimension.sync_block(block.x + offset.x, block.y + offset.y, block.z + offset.z);
 							hotbar_slot.amount! -= 1;
 						}
 					}
diff --git a/client/systems/render_system.ts b/client/systems/render_system.ts
index 233e418..4bb0c76 100644
--- a/client/systems/render_system.ts
+++ b/client/systems/render_system.ts
@@ -1,5 +1,4 @@
 import { System } from "$/common/ecs/mod.ts";
-import { World } from "$/common/ecs/world.ts";
 import { Position } from "$/common/components/position.ts";
 import { AnimatedSprite, Sprite } from "$/client/components/sprite.ts";
 import { Dimension } from "../components/dimension.ts";
@@ -10,13 +9,15 @@ import { render_dimension } from "./rendering/dimension.ts";
 import { render_player_breaking, render_player_crosshair, render_player_hotbar } from "./rendering/player.ts";
 import { PlayerComponent } from "../player.ts";
 import { begin_mode_3d, end_mode_3d } from "../renderer/core.ts";
+import { ClientWorld } from "../client_world.ts";
+import { render_chat_log, render_remote_players } from "./rendering/network.ts";
 
 export class RenderSystem extends System {
 	constructor() {
 		super();
 	}
 
-	update(world: World, _delta: number): void {
+	update(world: ClientWorld, _delta: number): void {
 		const camera_entity = world.get_entities().values().find((e) => e.get(Camera));
 		const camera = camera_entity?.get(Camera);
 
@@ -39,6 +40,10 @@ export class RenderSystem extends System {
 			}
 		}
 
+		if (world.connection) {
+			render_remote_players(world.connection);
+		}
+
 		end_mode_3d();
 
 		for (const entity of world.get_entities()) {
@@ -60,5 +65,7 @@ export class RenderSystem extends System {
 				render_player_crosshair();
 			}
 		}
+
+		render_chat_log(world, false);
 	}
 }
diff --git a/client/systems/rendering/network.ts b/client/systems/rendering/network.ts
new file mode 100644
index 0000000..f624d06
--- /dev/null
+++ b/client/systems/rendering/network.ts
@@ -0,0 +1,53 @@
+import { ClientWorld } from "$/client/client_world.ts";
+import { Connection } from "$/client/network.ts";
+import {
+	canvas,
+	draw_rect,
+	draw_text,
+	flush_batch,
+	push_box,
+	set_current_texture,
+	white_tex,
+} from "$/client/renderer/mod.ts";
+
+const CHAT_LINE_HEIGHT = 24;
+const CHAT_VISIBLE_SECONDS = 10;
+const CHAT_MAX_LINES = 10;
+
+export function render_remote_players(connection: Connection) {
+	if (connection.players.size === 0) {
+		return;
+	}
+
+	flush_batch();
+	set_current_texture(white_tex!);
+
+	for (const player of connection.players.values()) {
+		const [r, g, b] = player.color;
+		const x = player.display_x;
+		const y = player.display_y;
+		const z = player.display_z;
+
+		// body
+		push_box(x - 0.3, y, z - 0.15, 0.6, 1.3, 0.3, r, g, b);
+		// head
+		push_box(x - 0.25, y + 1.3, z - 0.25, 0.5, 0.5, 0.5, 0.95, 0.8, 0.65);
+	}
+
+	flush_batch();
+}
+
+// draws the chat log above the bottom left corner, `all` shows old messages too (when the chat is open)
+export function render_chat_log(world: ClientWorld, all: boolean, bottom = canvas.height - 100) {
+	const now = performance.now();
+	const lines = world.chat_log
+		.filter((line) => all || now - line.time < CHAT_VISIBLE_SECONDS * 1000)
+		.slice(-CHAT_MAX_LINES);
+
+	let y = bottom - lines.length * CHAT_LINE_HEIGHT;
+	for (const line of lines) {
+		draw_rect(0, y, 600, CHAT_LINE_HEIGHT, [0, 0, 0, 0.4]);
+		draw_text(line.text, 4, y, 2, [1, 1, 1, 1]);
+		y += CHAT_LINE_HEIGHT;
+	}
+}
diff --git a/common/constants.ts b/common/constants.ts
index d3732e4..39e3c57 100644
--- a/common/constants.ts
+++ b/common/constants.ts
@@ -18,3 +18,7 @@ export const VOID = 0xFFFFFFFF;
 
 export const ID_MASK = 0xFFFF;
 export const STATE_SHIFT = 16;
+
+export const CHUNK_SIZE = 16;
+export const CHUNK_HEIGHT = 128;
+export const CHUNK_AREA = CHUNK_SIZE * CHUNK_SIZE;
diff --git a/common/protocol.ts b/common/protocol.ts
new file mode 100644
index 0000000..21d1fce
--- /dev/null
+++ b/common/protocol.ts
@@ -0,0 +1,33 @@
+// messages sent between the client and the server, as json over a websocket
+
+export const AIR_ID = "bworld:air";
+
+export interface PlayerInfo {
+	id: string;
+	name: string;
+	x: number;
+	y: number;
+	z: number;
+	yaw: number;
+	pitch: number;
+}
+
+// x, y, z, block id
+export type BlockChange = [number, number, number, string];
+
+export type ClientMessage =
+	| { type: "hello"; name: string }
+	| { type: "move"; x: number; y: number; z: number; yaw: number; pitch: number }
+	| { type: "set_block"; x: number; y: number; z: number; id: string }
+	| { type: "chat"; text: string };
+
+export type ServerMessage =
+	| { type: "welcome"; id: string; seed: string; players: PlayerInfo[]; changes: BlockChange[] }
+	| { type: "player_join"; player: PlayerInfo }
+	| { type: "player_leave"; id: string }
+	| { type: "player_move"; id: string; x: number; y: number; z: number; yaw: number; pitch: number }
+	| { type: "set_block"; x: number; y: number; z: number; id: string }
+	| { type: "chat"; from?: string; text: string };
+
+export const MAX_NAME_LENGTH = 16;
+export const MAX_CHAT_LENGTH = 256;
diff --git a/deno.json b/deno.json
index 0ab7a5f..2fe818d 100644
--- a/deno.json
+++ b/deno.json
@@ -1,7 +1,8 @@
 {
 	"tasks": {
 		"build": "deno run -A build.ts",
-		"serve:client": "deno run --allow-net --allow-read jsr:@std/http/file-server build"
+		"serve:client": "deno run --allow-net --allow-read jsr:@std/http/file-server build",
+		"server": "deno run --allow-net --allow-read --allow-write --allow-env server/main.ts"
 	},
 	"compilerOptions": {
 		"lib": ["dom", "dom.asynciterable", "dom.iterable", "deno.ns", "deno.unstable"]
@@ -18,6 +19,7 @@
 		"@gfx/canvas-wasm": "jsr:@gfx/canvas-wasm@^0.4.2",
 		"@paulaboks/rng": "jsr:@paulaboks/rng@^0.0.3",
 		"@std/fs": "jsr:@std/fs@^1.0.23",
+		"@std/http": "jsr:@std/http@^1.0.23",
 		"gl-matrix": "npm:gl-matrix@^3.4.4",
 		"marked": "npm:marked@^17.0.3"
 	}
diff --git a/deno.lock b/deno.lock
index 70ab4b2..6020ca8 100644
--- a/deno.lock
+++ b/deno.lock
@@ -3,10 +3,20 @@
   "specifiers": {
     "jsr:@gfx/canvas-wasm@~0.4.2": "0.4.2",
     "jsr:@paulaboks/rng@^0.0.3": "0.0.3",
+    "jsr:@std/cli@^1.0.27": "1.0.27",
     "jsr:@std/encoding@1.0.5": "1.0.5",
+    "jsr:@std/encoding@^1.0.10": "1.0.10",
+    "jsr:@std/fmt@^1.0.9": "1.0.10",
+    "jsr:@std/fs@^1.0.22": "1.0.23",
     "jsr:@std/fs@^1.0.23": "1.0.23",
+    "jsr:@std/html@^1.0.5": "1.0.5",
+    "jsr:@std/http@*": "1.0.24",
+    "jsr:@std/http@^1.0.23": "1.0.24",
     "jsr:@std/internal@^1.0.12": "1.0.12",
+    "jsr:@std/media-types@^1.1.0": "1.1.0",
+    "jsr:@std/net@^1.0.6": "1.0.6",
     "jsr:@std/path@^1.1.4": "1.1.4",
+    "jsr:@std/streams@^1.0.17": "1.1.2",
     "npm:gl-matrix@^3.4.4": "3.4.4",
     "npm:marked@^17.0.3": "17.0.3"
   },
@@ -14,15 +24,24 @@
     "@gfx/canvas-wasm@0.4.2": {
       "integrity": "d653be3bd12cb2fa9bbe5d1b1f041a81b91d80b68502761204aaf60e4592532a",
       "dependencies": [
-        "jsr:@std/encoding"
+        "jsr:@std/encoding@1.0.5"
       ]
     },
     "@paulaboks/rng@0.0.3": {
       "integrity": "8d2571f9f406dab2674178f4034825cc654c5a52aa7c2a176a25f8b713eee202"
     },
+    "@std/cli@1.0.27": {
+      "integrity": "eba97edd0891871a7410e835dd94b3c260c709cca5983df2689c25a71fbe04de"
+    },
     "@std/encoding@1.0.5": {
       "integrity": "ecf363d4fc25bd85bd915ff6733a7e79b67e0e7806334af15f4645c569fefc04"
     },
+    "@std/encoding@1.0.10": {
+      "integrity": "8783c6384a2d13abd5e9e87a7ae0520a30e9f56aeeaa3bdf910a3eaaf5c811a1"
+    },
+    "@std/fmt@1.0.10": {
+      "integrity": "90dfba288802ac6de82fb31d0917eb9e4450b9925b954d5e51fc29ac07419db5"
+    },
     "@std/fs@1.0.23": {
       "integrity": "3ecbae4ce4fee03b180fa710caff36bb5adb66631c46a6460aaad49515565a37",
       "dependencies": [
@@ -30,14 +49,40 @@
         "jsr:@std/path"
       ]
     },
+    "@std/html@1.0.5": {
+      "integrity": "4e2d693f474cae8c16a920fa5e15a3b72267b94b84667f11a50c6dd1cb18d35e"
+    },
+    "@std/http@1.0.24": {
+      "integrity": "4dd59afd7cfd6e2e96e175b67a5a829b449ae55f08575721ec691e5d85d886d4",
+      "dependencies": [
+        "jsr:@std/cli",
+        "jsr:@std/encoding@^1.0.10",
+        "jsr:@std/fmt",
+        "jsr:@std/fs@^1.0.22",
+        "jsr:@std/html",
+        "jsr:@std/media-types",
+        "jsr:@std/net",
+        "jsr:@std/path",
+        "jsr:@std/streams"
+      ]
+    },
     "@std/internal@1.0.12": {
       "integrity": "972a634fd5bc34b242024402972cd5143eac68d8dffaca5eaa4dba30ce17b027"
     },
+    "@std/media-types@1.1.0": {
+      "integrity": "c9d093f0c05c3512932b330e3cc1fe1d627b301db33a4c2c2185c02471d6eaa4"
+    },
+    "@std/net@1.0.6": {
+      "integrity": "110735f93e95bb9feb95790a8b1d1bf69ec0dc74f3f97a00a76ea5efea25500c"
+    },
     "@std/path@1.1.4": {
       "integrity": "1d2d43f39efb1b42f0b1882a25486647cb851481862dc7313390b2bb044314b5",
       "dependencies": [
         "jsr:@std/internal"
       ]
+    },
+    "@std/streams@1.1.2": {
+      "integrity": "0249bf9b78a999f57032ca4d8e7ccaa57579090242640b35ddc948fbb745d3af"
     }
   },
   "npm": {
@@ -54,6 +99,7 @@
       "jsr:@gfx/canvas-wasm@~0.4.2",
       "jsr:@paulaboks/rng@^0.0.3",
       "jsr:@std/fs@^1.0.23",
+      "jsr:@std/http@^1.0.23",
       "npm:gl-matrix@^3.4.4",
       "npm:marked@^17.0.3"
     ]
diff --git a/server/main.ts b/server/main.ts
new file mode 100644
index 0000000..032cd23
--- /dev/null
+++ b/server/main.ts
@@ -0,0 +1,256 @@
+import { serveDir } from "@std/http/file-server";
+import { CHUNK_HEIGHT } from "$/common/constants.ts";
+import {
+	BlockChange,
+	ClientMessage,
+	MAX_CHAT_LENGTH,
+	MAX_NAME_LENGTH,
+	PlayerInfo,
+	ServerMessage,
+} from "$/common/protocol.ts";
+
+const PORT = Number(Deno.env.get("PORT") ?? 8000);
+const WORLD_FILE = Deno.env.get("WORLD_FILE") ?? "world.json";
+const STATIC_ROOT = "build";
+const SAVE_INTERVAL_MS = 30_000;
+const MAX_MESSAGE_SIZE = 4096;
+// how far from a player a block can be changed, a bit more than the client's reach
+const MAX_REACH = 8;
+
+const BLOCK_ID_PATTERN = /^[a-z0-9_]+:[a-z0-9_]+$/;
+
+interface SavedWorld {
+	seed: string;
+	changes: BlockChange[];
+}
+
+interface Client {
+	socket: WebSocket;
+	player?: PlayerInfo;
+}
+
+// the server doesnt generate terrain, clients do that from the seed
+// we only keep track of what players changed on top of it
+class ServerWorld {
+	seed: string;
+	changes = new Map<string, BlockChange>();
+	dirty = false;
+
+	constructor(seed: string) {
+		this.seed = seed;
+	}
+
+	set_block(x: number, y: number, z: number, id: string) {
+		this.changes.set(`${x},${y},${z}`, [x, y, z, id]);
+		this.dirty = true;
+	}
+
+	static load(path: string): ServerWorld {
+		try {
+			const saved: SavedWorld = JSON.parse(Deno.readTextFileSync(path));
+			const world = new ServerWorld(saved.seed);
+			for (const [x, y, z, id] of saved.changes) {
+				world.changes.set(`${x},${y},${z}`, [x, y, z, id]);
+			}
+			console.log(`Loaded ${path} (${world.changes.size} block changes)`);
+			return world;
+		} catch (e) {
+			if (!(e instanceof Deno.errors.NotFound)) {
+				throw e;
+			}
+			const world = new ServerWorld(Deno.env.get("SEED") ?? crypto.randomUUID());
+			world.dirty = true;
+			console.log(`Created new world with seed ${world.seed}`);
+			return world;
+		}
+	}
+
+	save(path: string) {
+		if (!this.dirty) {
+			return;
+		}
+		const saved: SavedWorld = { seed: this.seed, changes: [...this.changes.values()] };
+		// write then rename so a crash mid write doesnt eat the world
+		Deno.writeTextFileSync(`${path}.tmp`, JSON.stringify(saved));
+		Deno.renameSync(`${path}.tmp`, path);
+		this.dirty = false;
+	}
+}
+
+const world = ServerWorld.load(WORLD_FILE);
+const clients = new Set<Client>();
+
+function send(client: Client, message: ServerMessage) {
+	if (client.socket.readyState === WebSocket.OPEN) {
+		client.socket.send(JSON.stringify(message));
+	}
+}
+
+function broadcast(message: ServerMessage, except?: Client) {
+	const data = JSON.stringify(message);
+	for (const client of clients) {
+		if (client !== except && client.player && client.socket.readyState === WebSocket.OPEN) {
+			client.socket.send(data);
+		}
+	}
+}
+
+function is_number(value: unknown): value is number {
+	return typeof value === "number" && Number.isFinite(value);
+}
+
+function is_int(value: unknown): value is number {
+	return Number.isInteger(value);
+}
+
+function clean_name(name: unknown): string {
+	const cleaned = typeof name === "string" ? name.replace(/[^A-Za-z0-9_]/g, "").slice(0, MAX_NAME_LENGTH) : "";
+	const base = cleaned || `player${Math.floor(Math.random() * 10000)}`;
+
+	// make it unique
+	const taken = new Set([...clients].map((c) => c.player?.name));
+	let final = base;
+	let i = 2;
+	while (taken.has(final)) {
+		final = `${base}${i}`;
+		i += 1;
+	}
+	return final;
+}
+
+function handle_message(client: Client, message: ClientMessage) {
+	if (!client.player) {
+		if (message.type !== "hello") {
+			return;
+		}
+		const player: PlayerInfo = {
+			id: crypto.randomUUID(),
+			name: clean_name(message.name),
+			x: 0,
+			y: 100,
+			z: 0,
+			yaw: 0,
+			pitch: 0,
+		};
+		send(client, {
+			type: "welcome",
+			id: player.id,
+			seed: world.seed,
+			players: [...clients].flatMap((c) => c.player ? [c.player] : []),
+			changes: [...world.changes.values()],
+		});
+		client.player = player;
+		broadcast({ type: "player_join", player }, client);
+		broadcast({ type: "chat", text: `${player.name} joined` });
+		console.log(`${player.name} joined (${clients.size} online)`);
+		return;
+	}
+
+	const player = client.player;
+
+	switch (message.type) {
+		case "move": {
+			const { x, y, z, yaw, pitch } = message;
+			if (![x, y, z, yaw, pitch].every(is_number)) {
+				return;
+			}
+			Object.assign(player, { x, y, z, yaw, pitch });
+			broadcast({ type: "player_move", id: player.id, x, y, z, yaw, pitch }, client);
+			break;
+		}
+		case "set_block": {
+			const { x, y, z, id } = message;
+			if (!is_int(x) || !is_int(y) || !is_int(z) || y < 0 || y >= CHUNK_HEIGHT) {
+				return;
+			}
+			if (typeof id !== "string" || !BLOCK_ID_PATTERN.test(id)) {
+				return;
+			}
+			const dx = x + 0.5 - player.x;
+			const dy = y + 0.5 - (player.y + 1.69);
+			const dz = z + 0.5 - player.z;
+			if (dx * dx + dy * dy + dz * dz > MAX_REACH * MAX_REACH) {
+				return;
+			}
+			world.set_block(x, y, z, id);
+			broadcast({ type: "set_block", x, y, z, id }, client);
+			break;
+		}
+		case "chat": {
+			if (typeof message.text !== "string") {
+				return;
+			}
+			const text = message.text.trim().slice(0, MAX_CHAT_LENGTH);
+			if (text.length === 0) {
+				return;
+			}
+			console.log(`<${player.name}> ${text}`);
+			broadcast({ type: "chat", from: player.name, text });
+			break;
+		}
+	}
+}
+
+function handle_socket(socket: WebSocket) {
+	const client: Client = { socket };
+
+	socket.addEventListener("open", () => {
+		clients.add(client);
+	});
+
+	socket.addEventListener("message", (event) => {
+		if (typeof event.data !== "string" || event.data.length > MAX_MESSAGE_SIZE) {
+			return;
+		}
+		let message: ClientMessage;
+		try {
+			message = JSON.parse(event.data);
+		} catch {
+			return;
+		}
+		if (typeof message !== "object" || message === null) {
+			return;
+		}
+		handle_message(client, message);
+	});
+
+	socket.addEventListener("close", () => {
+		clients.delete(client);
+		if (client.player) {
+			broadcast({ type: "player_leave", id: client.player.id });
+			broadcast({ type: "chat", text: `${client.player.name} left` });
+			console.log(`${client.player.name} left (${clients.size} online)`);
+		}
+	});
+}
+
+setInterval(() => world.save(WORLD_FILE), SAVE_INTERVAL_MS);
+
+function shutdown() {
+	console.log("Saving world...");
+	world.save(WORLD_FILE);
+	Deno.exit(0);
+}
+Deno.addSignalListener("SIGINT", shutdown);
+if (Deno.build.os !== "windows") {
+	Deno.addSignalListener("SIGTERM", shutdown);
+}
+
+Deno.serve({ port: PORT, onListen: ({ port }) => console.log(`bworld server on http://localhost:${port}/`) }, (req) => {
+	const url = new URL(req.url);
+
+	if (url.pathname === "/ws") {
+		if (req.headers.get("upgrade")?.toLowerCase() !== "websocket") {
+			return new Response("Expected a websocket", { status: 426 });
+		}
+		const { socket, response } = Deno.upgradeWebSocket(req);
+		handle_socket(socket);
+		return response;
+	}
+
+	if (url.pathname === "/") {
+		return Response.redirect(new URL("/client/", url), 302);
+	}
+
+	return serveDir(req, { fsRoot: STATIC_ROOT, quiet: true });
+});