After its 0.24.1 release a week ago I decided to give Crystal a whirl. It’s been around since 2014 but is gaining traction.

I started my programming journey hacking on PHP in 2001 and grew into a developer with Ruby and its clean syntax. I’ve dabbled in Go but didn’t care for the syntax. I’ve dabbled in Elixir but had a hard time getting my app deployed with the right Erlang/OTP dependencies. Crystal ticks most of the boxes I care about:

  • Clean, familiar syntax
  • Fast!
  • Easy compilation to a single, easily-deployable binary
  • Modern standard library
  • Nice documentation

As its slogan says: “Fast as C, slick as Ruby.”

It also has a mature Sinatra-like web mini-framework called Kemal and an incubating-by-Rails-consultancy-juggernaut-Thoughtbot framework called Lucky which is shaping up nicely.

Getting Started

Installing Crystal on Mac is pretty easy with Homebrew: brew install crystal-lang.

Here’s a simple Hello World app:

puts "Hello World"

Run with crystal run or build a binary with crystal build

The syntax is identical to Ruby in most simple cases, but it’s not Ruby. For example, it can have types:

class Person
  def initialize(name : String)
    @name = name
    @age = 0

  def name

  def age

kevin ="Kevin") #=> "Kevin"

Sinatra vs. Kemal

I coded up a quick Sinatra “Hello World” app (which I can do mostly from memory) and a similar one in Kemal to give you a flavor of what it’s like to get started in Crystal.


require "sinatra"

get "/" do
  "Hello World!"

Now let’s run and benchmark it:

% RACK_ENV=production ruby sinatra.rb # run
% wrk -c16 -t16 -d30s http://localhost:4567/ # benchmark
Running 30s test @ http://localhost:4567/
  16 threads and 16 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     6.41ms    7.87ms 178.16ms   91.30%
    Req/Sec   177.17     38.21   303.00     71.07%
  63540 requests in 30.09s, 11.21MB read
Requests/sec:   2111.50
Transfer/sec:    381.50KB


require "kemal"

get "/" do
  "Hello World!"

(Looks familiar, eh?) Let’s (compile!), run, and benchmark:

% crystal build --release # compile
% ./kemal # run
% wrk -c16 -t16 -d30s http://localhost:3000/ # benchmark
Running 30s test @ http://localhost:3000/
  16 threads and 16 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     2.69ms    9.52ms 223.64ms   94.47%
    Req/Sec     1.34k   291.21     1.89k    71.22%
  639215 requests in 30.04s, 73.76MB read
Requests/sec:  21280.90
Transfer/sec:      2.46MB

About an order-of-magnitude faster! (Don’t you just love a good microbenchmark?) Plus we didn’t have to sacrifice any of the clean, familiar syntax of Ruby.

Crystal in Crystal

As I dove deeper, I learned Crystal is (mostly) implemented in Crystal, especially its standard library. (Kind of like Rubinius, remember that?) And its a modern one with built-in JSON parsing and generation support and a nice HTTP client, for example.

Since things are just ramping up the barrier of entry to contributing to Crystal and its fledgling libraries is pretty low. Especially since you don’t have to write C to contribute.

Growing Crystal

I’m skeptical about Crystal’s long term future, and probably won’t use it for any client apps at the moment, but I am digging into it for side projects and starting to advocate for it in small areas where is makes sense in the hopes that it may one day get the support it needs to grow.