About this guide

This is a formal specification of the Crystal language.

You can read this document from top to bottom, but it’s advisable to jump through sections because some concepts are interrelated and can’t be explained in isolation.

The Language Introduction tutorial offers a more focused learning experience for beginners.

In code examples, a comment starting with # => shows the value of an expression.

  1. 1 + 2 # => 3

A comment starting with # : shows the type of an expression.

  1. "hello" # : String