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ICR - Interactive Crystal Build Status

Interactive console for Crystal Programming Language.


It's like irb, but for Crystal:

GIF demo

Require local files

You can require local files by relative path (starts with ./):

require "./src/my_cool_lib"

Libs can also be required from the cli:

$ icr -r colorize -r ./src/my_cool_lib



  • The latest version of crystal.
  • Readline (for Debian/Ubuntu install libreadline6-dev package).
  • LLVM development files.

Clone the repo:

git clone

Switch to repo-directory:

cd icr




sudo make install

As a shard dependency

If you would like to include icr as a dependency, you can add it to your shard.yml

    github: crystal-community/icr
    branch: master

Then just run shards install from your project!


Arch Linux

Arch Linux users can install ICR from AUR.

How does it work?

  • Every time you press Enter it adds a new instruction, generates a new crystal program, and executes it.
  • The output is split into 2 parts: regular program output (e.g. output from puts 10) and the value returned by the last command.
  • The regular output is saved, and when you type a new instruction, a new program is generated. The saved output is subtracted from the new output, and the difference is printed out. It creates an illusion that only new instructions are executed :)

Commands and special locals

  • paste - enables paste mode
  • debug - toggles debug mode off and on. In debug mode icr will print the code before executing it
  • quit or exit - exits current interactive console
  • reset - clears out all of the accumulated commands
  • __ - holds the result of the last expression. Example:
icr > "5" + "2"
=> "52"
icr > __.to_i - 10
=> 42

Update check

ICR periodically checks for the new releases on Github. If your current version is out of date, it will simply show you a notice at start.

You can disable this behavior using --disable-update-check CLI flag.


To run tests:

make test

Editor integration

  • inf-crystal.el - Connects REPL buffer to the ICR subprocess in Emacs


  • greyblake Potapov Sergey - creator, maintainer
  • BlaXpirit Oleh Prypin - fixes for Crystal 0.16
  • puppetpies Brian Hood - support of records
  • jwoertink Jeremy Woertink - support of -r option and number of other contributions
  • veelenga V. Elenhaupt - maintenance
  • MakeNowJust TSUYUSATO Kitsune - syntax highlight support