Programming Minecraft with Websockets - S Anand (2023)

Minecraft lets you connect to a websocket server when you’re in a game. The server can receive and send any commands. This lets you build a bot that you can … (well, I don’t know what it can do, let’s explore.)

Minecraft hascommandsyou can type on a chat window. For example, type/to start a command and typesetblock ~1 ~0 ~0 grasschanges the block 1 north of you into grass. (~means relative to you. Coordinates are specified as X, Y and Z.)

Note: These instructions were tested on Minecraft Bedrock 1.16. I haven’t tested them on the Java Edition.

Connect to Minecraft

You can send any command to Minecraft from a websocket server. Let’s use JavaScript for this.

First, runnpm install ws uuid. (We needwsfor websockets anduuidto generate unique IDs.)

Then create thismineserver1.js:

const WebSocket = require('ws')const uuid = require('uuid') // For later use// Create a new websocket server on port 3000console.log('Ready. On MineCraft chat, type /connect localhost:3000')const wss = new WebSocket.Server({ port: 3000 })// On Minecraft, when you type "/connect localhost:3000" it creates a connectionwss.on('connection', socket => { console.log('Connected')})

On Minecraft > Settings > General > Profile, turn off the “Require Encrypted Websockets” setting.

Runnode mineserver1.js. Then type/connect localhost:3000in a Minecraft chat window. You’ll see 2 things:

1. MineCraft says “Connection established to server: ws://localhost:3000”
2. Node prints “Connected”

Now, our program is connected to Minecraft, and can send/receive messages.

Notes:

• The Python equivalent is inmineserver1.py. Runpython mineserver1.py.
• If you get anUncaught Error: Cannot find module 'ws', make sure you rannpm install ws uuid.
• If you get an “Encrypted Session Required” error, make sure you turned off the “Require Encrypted Websockets” setting mentioned above.
• To disconnect, run/connect off

Subscribe to chat messages

Now let’s listen to the players’ chat.

A connected websocket server can send a “subscribe” message to Minecraft saying it wants to “listen” to specific actions. For example, you can subscribe to “PlayerMessage”. Whenever a player sents a chat message, Minecraft will notify the websocket client.

Here’s how to do that. Add this code in thewss.on('connection', socket => { ... })function.

 // Tell Minecraft to send all chat messages. Required once after Minecraft starts socket.send(JSON.stringify({ "header": { "version": 1, // We're using the version 1 message protocol "requestId": uuid.v4(), // A unique ID for the request "messageType": "commandRequest", // This is a request ... "messagePurpose": "subscribe" // ... to subscribe to ... }, "body": { "eventName": "PlayerMessage" // ... all player messages. }, }))

Now, every time a player types something in the chat window, the socket will receive it. Add this code below the above code:

 // When MineCraft sends a message (e.g. on player chat), print it. socket.on('message', packet => { const msg = JSON.parse(packet) console.log(msg) })

This code parses all the messages it receives and prints them.

This code in ismineserver2.js. Runnode mineserver2.js. Then type/connect localhost:3000in a Minecraft chat window. Then type a message (e.g. “alpha”) in the chat window. You’ll see a message like this in the console.

{ header: { messagePurpose: 'event', // This is an event requestId: '00000000-0000-0000-0000-000000000000', version: 1 // using version 1 message protocol }, body: { eventName: 'PlayerMessage', measurements: null, properties: { AccountType: 1, ActiveSessionID: 'e0afde71-9a15-401b-ba38-82c64a94048d', AppSessionID: 'b2f5dddc-2a2d-4ec1-bf7b-578038967f9a', Biome: 1, // Plains Biome. https://minecraft.gamepedia.com/Biome Build: '1.16.201', // That's my build BuildNum: '5131175', BuildPlat: 7, Cheevos: false, ClientId: 'fcaa9859-0921-348e-bc7c-1c91b72ccec1', CurrentNumDevices: 1, DeviceSessionId: 'b2f5dddc-2a2d-4ec1-bf7b-578038967f9a', Difficulty: 'NORMAL', // I'm playing on normal difficulty Dim: 0, GlobalMultiplayerCorrelationId: '91967b8c-01c6-4708-8a31-f111ddaa8174', Message: 'alpha', // This is the message I typed MessageType: 'chat', // It's of type chat Mode: 1, NetworkType: 0, Plat: 'Win 10.0.19041.1', PlayerGameMode: 1, // Creative. https://minecraft.gamepedia.com/Commands/gamemode Sender: 'Anand', // That's me. Seq: 497, WorldFeature: 0, WorldSessionId: '8c9b4d3b-7118-4324-ba32-c357c709d682', editionType: 'win10', isTrial: 0, locale: 'en_IN', vrMode: false } }}

Notes:

• The Python equivalent is inmineserver2.py. Runpython mineserver2.py.
• The official Minecraft docs say that theMCWSS protocol is outdated. But it seems to work.
• The full list of things we can subscribe to is undocumented, but@jocopa3has reverse-engineered alist of messageswe can subscribe to, and they’re somewhat meaningful.
• This Go packagehas code that explores theprotocolfurther.
• Thischathas more details. There’s also anoutdated list of JSON messagesfrom@jocopa3.
• Here’s a sample program thatplaces a block in Minecraft

Build structures using chat

Let’s create a pyramid of size10around us when we typepyramid 10in the chat window.

The first step is to check if the player sent a chat message likepyramid 10(or another number). Add this code below the above code:

 // When MineCraft sends a message (e.g. on player chat), act on it. socket.on('message', packet => { const msg = JSON.parse(packet) // If this is a chat window if (msg.body.eventName === 'PlayerMessage') { // ... and it's like "pyramid 10" (or some number), draw a pyramid const match = msg.body.properties.Message.match(/^pyramid (\d+)/i) if (match) draw_pyramid(+match[1]) } })

If the user types “pyramid 3” on the chat window,draw_pyramid(3)is called.

Indraw_pyramid(), let’s send commands to build a pyramid. To send a command, we need to create a JSON with the command (e.g.setblock ~1 ~0 ~0 grass). Add this code below the above code:

 function send(cmd) { const msg = { "header": { "version": 1, "requestId": uuid.v4(), // Send unique ID each time "messagePurpose": "commandRequest", "messageType": "commandRequest" }, "body": { "version": 1, // TODO: Needed? "commandLine": cmd, // Define the command "origin": { "type": "player" // Message comes from player } } } socket.send(JSON.stringify(msg)) // Send the JSON string }

Let’s writedraw_pyramid()to create a pyramid using glowstone by adding this code below the above code:

 // Draw a pyramid of size "size" around the player. function draw_pyramid(size) { // y is the height of the pyramid. Start with y=0, and keep building up for (let y = 0; y < size + 1; y++) { // At the specified y, place blocks in a rectangle of size "side" let side = size - y; for (let x = -side; x < side + 1; x++) { send(`setblock ~${x} ~${y} ~${-side} glowstone`) send(`setblock ~${x} ~${y} ~${+side} glowstone`) send(`setblock ~${-side} ~${y} ~${x} glowstone`) send(`setblock ~${+side} ~${y} ~${x} glowstone`) } } }

This code in ismineserver3.js.

• Runnode mineserver3.js.
• Then type/connect localhost:3000in a Minecraft chat window.
• Then typepyramid 3in the chat window.
• You’ll be surrounded by a glowstone pyramid.

Notes:

• The Python equivalent is inmineserver3.py. Runpython mineserver3.py.
• The “requestId” needs to be a UUID — at least for block commands. I tried unique “requestId” values like 1, 2, 3 etc. That didn’t work.

Understand Minecraft’s responses

For every command you send, Minecraft sends a response. It’s “header” looks like this:

{ "header": { "version": 1, "messagePurpose": "commandResponse", // Response to your command "requestId": "97dee9a3-a716-4caa-aef9-ddbd642f2650" // ... and your requestId }}

If the command is successful, the response hasbody.statusCode == 0. For example:

{ "body": { "statusCode": 0, // No error "statusMessage": "Block placed", // It placed the block you wanted "position": { "x": 0, "y": 64, "z": 0 } // ... at this location },}

If the command failed, the response has a negativebody.statusCode. For example:

{ "body": { "statusCode": -2147352576, // This is an error "statusMessage": "The block couldn't be placed" },}

To print these, add this tosocket.on('message', ...):

 // If we get a command response, print it if (msg.header.messagePurpose == 'commandResponse') console.log(msg)

This code in ismineserver4.js.

• Runnode mineserver4.js.
• Then type/connect localhost:3000in a Minecraft chat window.
• Then typepyramid 3in the chat window.
• You’ll be surrounded by a glowstone pyramid, and theconsole will show every command response.

Notes on common error messages:

• The block couldn't be placed(-2147352576): The same block was already at that location.
• Syntax error: Unexpected "xxx": at "~0 ~9 ~-1 >>xxx<<"(-2147483648): You gave wrong arguments to the command.
• Too many commands have been requested, wait for one to be done(-2147418109): Minecraft only allows 100 commands can be executed without waiting for their response.
• More error messages here.

Wait for commands to be done

Typing “pyramid 3” works just fine. But try “pyramid 5” and your pyramid is incomplete.

That’s because Minecraft only allows up to 100 messages in its queue. On the 101st message, you get aToo many commands have been requested, wait for one to be doneerror.

{ "header": { "version": 1, "messagePurpose": "error", "requestId": "a5051664-e9f4-4f9f-96b8-a56b5783117b" }, "body": { "statusCode": -2147418109, "statusMessage": "Too many commands have been requested, wait for one to be done" }}

So let’s modifysend()to add to a queue and send in batches. We’ll create two queues:

 const sendQueue = [] // Queue of commands to be sent const awaitedQueue = {} // Queue of responses awaited from Minecraft

Inwss.on('connection', ...), when Minecraft completes a command, we’ll remove it from theawaitedQueue. If the command has an error, we’ll report it.

 // If we get a command response if (msg.header.messagePurpose == 'commandResponse') { // ... and it's for an awaited command if (msg.header.requestId in awaitedQueue) { // Print errors 5(if any) if (msg.body.statusCode < 0) console.log(awaitedQueue[msg.header.requestId].body.commandLine, msg.body.statusMessage) // ... and delete it from the awaited queue delete awaitedQueue[msg.header.requestId] } } // Now, we've cleared all completed commands from the awaitedQueue.

Once we’ve processed Minecraft’s response, we’ll send pending messages fromsendQueue, upto 100 and add them to theawaitedQueue.

 // We can send new commands from the sendQueue -- up to a maximum of 100. let count = Math.min(100 - Object.keys(awaitedQueue).length, sendQueue.length) for (let i = 0; i < count; i++) { // Each time, send the first command in sendQueue, and add it to the awaitedQueue let command = sendQueue.shift() socket.send(JSON.stringify(command)) awaitedQueue[command.header.requestId] = command } // Now we've sent as many commands as we can. Wait till the next PlayerMessage/commandResponse

Finally, in function send(), instead ofsocket.send(JSON.stringify(msg)), we usesendQueue.push(msg)to add the message to the queue.

This code in ismineserver5.js.

• Runnode mineserver5.js.
• Then type/connect localhost:3000in a Minecraft chat window.
• Then typepyramid 6in the chat window.
• You’ll be surrounded by a large glowstone pyramid.
• The console will print messages likesetblock ~0 ~6 ~0 glowstone The block couldn't be placedbecause we’re trying to place duplicate blocks.