0.0.6 • Public • Published


This is a from-scratch rewrite of the Screeps backend services, brought to you by the author of the path finder and also isolated-vm. The goal of this project is to build a very fast version of the Screeps backend service which will greatly improve upon the local single-player experience, and perhaps eventually the multiplayer world as well.



At the heart of xxscreeps is a custom binary format created specifically to efficiently represent the state of a room. Instead of storing a sea of objects indexed by room in a shared database, each room is stored as a blob ranging in size from 250 bytes to 60kb for most rooms. A room blob represents game state in the same way a C program might represent it. For reference, a simple object like a StructureWall can be represented in 44 bytes, and a creep with a fully loaded 50-length body is about 274 bytes.

Hex Dump

The first advantage of this is greatly improved performance of the runner service. Game state is read from the database as an ArrayBuffer which can be instantly transferred into the player's runtime for free. In vanilla Screeps the process of requesting game state from the database and loading it into the runner requires several costly serialization and deserialization steps.

The real crazy part is that we can overlay JavaScript game state directly on top of these room blobs. Inherited getters are created which reach into the blob and pull out game state as it requested by the user's script. So, for example, if you go an entire tick without accessing the body property on a Creep, that array along with all its contents will never be materialized into the v8 heap. This greatly reduces the burden of the garbage collector which robs every player of a significant portion of CPU.

Storage of room blobs can be efficiently sharded within a world shard as well. These blobs are no different than a very small JPEG file, like from the 90's. We could theoretically infinitely scale a game world in all directions by linearly adding more processor workers.


In xxscreeps room processing can begin as soon as all player scripts in a single room have completed. Most rooms are only accessible by 1 or maybe 2 users at a time. Right now in vanilla Screeps the processor service just sits around doing nothing until all player scripts are done. By overlapping running and processing we can improve scalability of a world shard.


Private class fields, proxies, reflection, and a custom Babel transform have simplified the player sandbox implementation. We can now share code between the runtime and processor and implement game logic using the same APIs that the player uses. Compare the work needed to implement a Creep's transfer method in xxscreeps: [Creep.prototype.transfer, checkTransfer, and 'transfer' intent] to the same feature in vanilla Screeps: [Creep.prototype.transfer, intents/creep/transfer.js]. Of course the functionality in xxscreeps is incomplete in some ways but the foundation is solid.


The "core" xxscreeps engine is meant to be abstract and extendable. Almost all game logic is implemented as mods which can be turned on and off independently of one and other. Even Creep objects are implemented a mod! As the scope of gameplay in Screeps has expanded over time it's become more difficult to reason about any one gameplay component since its logic might be scattered over many different and unrelated files. Furthermore by "dogfooding" the mods API we will be confident that it's powerful and easy as possible to use.


There's a lot of factors that can make Screeps difficult to work with. Every player of Screeps knows the disappointment of typing console.log(creep) into the console and seeing [Object object] echoed back. xxscreeps comes with robust console support just like you get in nodejs. Full support for the Chrome Web Inspector or VS Code debugger is planned as well, which will make it possible to step through your script line by line to troubleshoot issues. Source map support is built-in to the player sandbox so if you use a transpiler (like TypeScript or Webpack) you will be able to see the original file name and line number in stack traces. And the whole thing is written with detailed TypeScript annotations and inline documentation as well which greatly improves the player's access to information about game APIs.

Console Example

Getting Started

To get xxscreeps running here's what you need to do. This should work on Linux, macOS, and Windows. First step is make sure nodejs v16.x is installed, older versions will not work.

git clone https://github.com/laverdet/xxscreeps.git
cd xxscreeps
npm install
npm run build
npx xxscreeps import

After that you can start xxscreeps via npx xxscreeps start except you won't be able to connect with the Steam client. You'll need to create a file .screepsrc.yaml with content:

  steamApiKey: <your steam key>

If you're using VS Code and you have the YAML extension installed all the options should autocomplete. If not you can read the config schema.


If you want to install xxscreeps via docker you can use the following docker-compose.yaml as an example.

version: "3"
    image: nilskri/xxscreeps
      - "21025:21025"
      - <your path to the .screepsrc.yaml you want to use>:/usr/app/xxscreeps/.screepsrc.yaml
# set this if you want to persist the content
#      - <path to persistence>:/usr/app/xxscreeps/screeps

Or you can use this short script in a fresh copy of the git source to start a new container which persists data to the current working directory.

docker build -t xxscreeps .
docker run -it -p 21025:21025 \
  --mount type=bind,source="$(pwd)"/.screepsrc.yaml,target=/usr/app/xxscreeps/.screepsrc.yaml \
  --mount type=bind,source="$(pwd)"/screeps,target=/usr/app/xxscreeps/screeps \


If you've read this far, hopefully you would like to help. Without support from the community xxscreeps will definitely fail and die.

If you are a novice developer the best thing you can do is help test and provide feedback. Install xxscreeps and get your scripts running and help find inaccuracies in the game engine. Troubleshooting is your most valuable contribution! A bug report of "my creeps are getting stuck when walking past sources" is not very helpful. A bug report of "findClosestByPath returns undefined instead of null when there is no result" or "transfer and withdraw don't transfer any resources when amount === 0; these functions should transfer the maximum amount possible in this case" is extraordinarily helpful.

If you are a professional developer and you want to help there's still a lot of features that need to be developed. Feel free to talk to me about the status of the project!


Join the official Screeps Discord. You can find me [The General] in the #xxscreeps channel.




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npm i xxscreeps

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  • laverdet