Crystal Snake

This is a Battle Snake project written in Crystal using Kemal

I strongly recommend reading the docs in You'll find detailed information on classes and methods there :)

I wrote a few blog posts about this project. Check out the first one here.


You'll need Crystal, Postgres & Redis locally. The app uses for ease of development.

# Install dependencies
shards install

# Create DB & run migrations
make sam db:setup

# Start development server in port 8080 with live reload
make sam dev

# Run tests
make sam test


The app can be configured copying the .env.sample file as .env in the directory root.

For local development I use the BattleSnake CLI with the local server running. A basic example looks like this:

# Solo game with ChaseClosestFood strategy
battlesnake play -W 11 -H 11 --name dev --url http://localhost:8080/chase_closest_food -g solo -v

# Play RandomValid vs CautiousCarol strategies
battlesnake play -W 11 -H 11 --name RandomValid --url http://localhost:8080/random_valid  --name CautiousCarol --url http://localhost:8080/cautious_carol -v

Strategies & Architecture

The server is built on the src/ file and you can choose to use any of the available strategies.

To start hacking a new one create a new strategy (in the src/strategy folder) that inherits from Stategy::Base. They're all initialized with a BattleSnake::Context and the server calls the #move method on it to respond with. You can re-use strategies within each other, i.e. Strategy::ChaseClosestFood uses the Strategy::RandomValid strategy when it can't reach any food on the board.

In order to start using a new strategy:

  1. Add new entry in case clause to src/strategy/
    • Must return the new strategy object
  2. The string in the case clause will determine its path
    • i.e. http://localhost:8080/new_strategy

Strategies can use Strategy::Utils class methods like Strategy::Utils.a_star which implements the A* Search Algorithm. Check out the available Utils helper methods.


I'm currently using DigitalOcean App Platform. The Dockerfile is detected and deployed on their cheapest tier. It "should work" in lots of other platforms with this setup, but open an issue if you need help troubleshooting or to discuss other solutions.


ENV variables are used to customize your snake


Make sure to test your changes. First copy .env.sample as .env.test so you can run the test suite with make sam test.

  1. Fork it (
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request