“Kotlin Quick Reference” book

Somewhere in mid-2017 I started working on a Kotlin programming book, but then I had to get away from it to work on other things. When I got back to it recently I looked around and felt like the world didn’t need another “Introduction to Kotlin” book — there are a couple of good ones out there, including Kotlin in Action, and the kotlinlang.org documentation is excellent — so I decided to ditch the project completely.

Kotlin Quick Reference

But then when I started writing some Kotlin code again I realized that what I really needed was a quick reference. I didn’t want to have to dig through a tutorial book or website to find what I need, I just wanted something like a large cheat sheet where I could quickly find the Kotlin syntax and examples for whatever I was working on at that moment. So I decided to strip down what I had already written and create both a book and a Kotlin Quick Reference website.

Kotlin Quick Reference cover

It’s free

Once I made that decision I made another decision: I decided to give it all away for free. The e-books and kotlin-quick-reference.com website are all completely free.

It’s open source

Another thing I decided to do was to make the book open source. I’m releasing the entire book — with the exception of the cover image — under the Attribution-ShareAlike 4.0 International license. My understanding is that this is a newer version of the license used by Wikipedia and others.

Cover image note: If you want to fork this project that’s fine, but it doesn’t make sense to have the same cover image on different books, so that’s one reason why the cover image is not open source. So, if you fork the project, create your own cover.

A caveat

At the moment there’s one caveat to this announcement: the book isn’t finished yet. If you take a look at the e-books or Kotlin Quick Reference website, you’ll see that I’ve put a lot of work into it, but it still has a ways to go. But hopefully it’s useful now, and it will be even more useful in the future.


If you know things about Kotlin that I don’t know yet (or haven’t had time to write about), I welcome you to contribute to the project. You can find all of the text at this Github URL:

If you’d like to work with me on this project, I hope the README.md file there explains what you’ll need to know to work on the project.

Note: I’ll be having an operation later this week (Surgery #8), so I’ll be out of commission from Thursday until some time next week (the week of December 10th). Also, I’m not working on this project full time, but I expect to give it ~4 hours a week for the foreseeable future.

The Kindle version

It turns out that you can’t easily give a book away for free on Amazon, so I’ve initially set the price of the book to $2.99. At the time of this writing Amazon hasn’t made the book available, but once it is available I’ll try to run what they call a “free promotion” indefinitely (if that’s possible). However, if that requires too much time I’ll just leave the price at $2.99.

I also want to note that the Kindle/MOBI version of the book is currently a little wonky, probably because I don’t know enough about how to use the Gitbook tools to generate a MOBI file. In particular the chapter numbering is off, and I don’t like the way it separates the content within chapters of the book. Hopefully this will be fixed soon. At the moment the website has the best formatting, and the PDF has the second-best formatting.


In addition to the kotlin-quick-reference.com website, you can find the e-books in the Github repository at these links:

I’ll link to the free Kindle version on Amazon as soon as they make that available.

I can also create an ePub version if people are interested in that.