Crate screeps

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Typed bindings to the Screeps: World in-game API for WASM Rust AIs.


Due to the limited CPU available to the player in Screeps: World, the performance implications of running WebAssembly are good to be aware of.

WebAssembly instances have a dedicated linear memory, and data being passed in or out must be copied. Additionally, Rust uses UTF-8 strings while JavaScript uses UTF-16 strings, so any strings being copied must also be converted between encodings.

Additionally, compile time for the WebAssembly.Module can be considerable, requiring a lot of CPU time on each initial startup tick (and potentially requiring skipped ticks for larger bots). However, global resets are very infrequent in most environments, so the impact of this isn’t severe.

After compilation, the WebAssembly environment has near-native performance, and no Javascript garbage collection happening for its memory space, allowing for faster execution of some types of workloads. Overall, the advantages and disadvantages of WebAssembly in Screeps are relatively small, especially when compared to the relatively high 0.2ms cost of game actions.

§Data Persistence

In the Screeps: World JavaScript environment, the Memory object is the typical way to store data in a way that persists through the environment resets that happen occasionally, either triggered by deploying a new version of your code or due to natural expiration in the server. It provides a wrapper that automatically deserializes the contents of RawMemory via the JSON.parse() JavaScript function when accessed for the first time each tick, then gets serialized by JSON.stringify() at the end of the tick.

Using this untyped Memory object (or the reference to a part of it, which can be obtained from the memory function on various game objects) from within WebAssembly can be awkward, but is recommended if you need to maintain compatibility with the default Memory object.

An alternative that you may prefer is to use RawMemory instead, fetching the stored data in string format using raw_memory::get and deserializing within WebAssembly using serde or another serializion approach, then serializing and using raw_memory::set to store the data.

If you choose the RawMemory approach, be aware that some game methods (notably StructureSpawn::spawn_creep and Creep::move_to) directly store data in the Memory object; replacing the ‘special’ Memory object with one that doesn’t attempt to deserialize the contents of RawMemory may be advisable if you’re using it directly (note that this needs to be done each tick to be effective).

§Cargo Features


Enables a number of functions for CPU management and inter-shard communication present on the Screeps: World official servers but not on private servers.


Enables the score resource and entities, introduced for Screeps Seasonal’s first season, as well as enabling constants relevant to season 1.


Enables the symbol resources and entities, introduced for Screeps Seasonal’s second season, as well as enabling constants relevant to season 2.


Enables the thorium resource and reactor object, introduced for Screeps Seasonal’s fifth season, as well as enabling constants relevant to season 5.


Enables special-case handling of the unique room name present in the simulator - must be enabled to build code that is compatible with that environment. If this is enabled, the top-left valid room coordinate has the name sim, otherwise it’s named W127N127.


Enables return code conversion from game functions that presumes all return code values are in the expected ranges skipping checks, and risks undefined behavior if they are not.



  • Utility functions for visuals that the game API exposes on the console object.
  • Constants, most copied from the game constants.
  • Enums using enum_dispatch for generic wrappers around object types with shared traits.
  • The main interface to objects in the Screeps game world.
  • Interface for Screeps inter-shard memory, allowing communication between instances of your code running on different shards.
  • Typed JavaScript collection wrappers.
  • Pure-data structures relating to Screeps.
  • Interface with Screeps’ Memory global variable
  • Screeps object wrappers.
  • Manually accessing the PathFinder API
  • Traits which implement base functionalities for Screeps types.
  • Interface for Screeps RawMemory global object.
  • Traits associated with how specific game objects can be used.