Crystal is a general-purpose, object-oriented programming language. The language is statically type-checked but does not require that the type of variables or method arguments be specified.

Although resembling the Ruby programming language in syntax, Crystal compiles to a much more efficient native code using an LLVM backend. This comes at the cost of disallowing the dynamic aspects of Ruby. However, the advanced global type inference used by the Crystal compiler, combined with the usage of union types, give Crystal the feel of a higher-level scripting language than many other comparable programming languages.