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COIN: CLI to currency conversion

coin is a command-line application that performs currency conversion via the Fixer API. It is currently able to convert monetary values up to 168 different currencies.


pd forthebadge didnt-ask

Table of Contents


user@host:~$ coin -h

Usage: coin [-h] [-v] amount origin <target, ...>

Positional arguments:
    amount             The amount of money to be converted
    origin             The origin currency used as base for conversion
    target             Each of the target currencies for conversion

Optional arguments:
    -h, --help         Show this help message and exit
    -v, --version      Show the program version and exit

    $ coin 1 usd brl
    # => converts 1 us dollar to brazilian real

    $ coin 2.5 eur rub jpy
    # => converts 2.5 euro to russian rouble and japanese yen

This project is dedicated to the Public Domain (CC0).

Project page: <>

For a comprehensive list of all available currencies, see docs/currencies.rst.

Fixer API token

Coin highly depends on Fixer, a "foreign exchange rates and currency conversion JSON API". Fixer gives a free tier that allows up to a 1000 requests per month. In order to get an API key and use the service, an account is required. You can sign up for a free account here.

The API key is a 32-length characters wide alphanumeric string. Coin must read this API key in order to make the request and parse it. It will, by default, try to read the key from the FIXER_API_TOKEN.

  • Export the API key:
$ export FIXER_API_TOKEN="ys1r39m5zc71xpvdjpqsnrhwqtxe98cj"



The pre-built binary is available at the release page. Download the most recent version, give the binary execution permissions and move to a directory on the $PATH.

$ wget
$ chmod +x coin
$ mv coin /usr/bin

From source

Coin is implemented in Crystal. In order to build from source you must have the Crystal compiler.

  • Clone the repository:
$ clone
  • Make and install:
$ make
$ (sudo) make install

Running in Docker

  • Pull from DockerHub:
$ docker pull caian/coin
  • Run the container:
$ docker run -e FIXER_API_TOKEN="my_token" caian/coin 1 usd jpy

Alternatively, you can build the Docker image yourself:

docker build -t coin .


Contributions are welcomed. You can contribute with bugfixes and minor features. For bigger, more complex features or architectural changes, please contact me beforehand.

If you wish to contribute:

  • Fork it (
  • Create your feature branch (git checkout -b my-new-feature)
  • Commit your changes (git commit -am 'Add some feature')
  • Push to the branch (git push origin my-new-feature)
  • Create a new Pull Request

Large contributions must contain a notice stating that the owner (i.e., the contributor) waive it's copyrights to the Public Domain.


To the extent possible under law, Caian Rais Ertl has waived all copyright and related or neighboring rights to this work.

Coin depends on optarg. optarg is licensed under the MIT license.

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