This ruby gem lets you fetch exchange rates for ~170 currencies (a total of ~14,000 imputed currency pairs) for free, on an hourly frequently (sufficient for most, but not all, use cases), and takes only about 5 minutes to set up.

The usage instructions below show how to create a currencies table, run a rake task to update the exchange rates, and use convert() to convert between currencies inside your application. Total time to implementation should be ~5 minutes.

Install the gem in one of the usual ways:

bundle add simple_forex

gem install simple_forex

Use the included generator will make a currencies table migration:

rails generate simple_forex

Then run the migration:

rake db:migrate

Create a free API key, open credentials.yml (EDITOR="vim" rails credentials:edit) and add the API key to credentials.yml like so:

# config/credentials.yml.enc

simple_forex:
  openexchangerates_key: 1234abcd

Run this rate task to retrieve currencies and store them in the currencies table:

rake simple_forex:fetch_rates

View the exchange rate data in the rails console with Currency.last:

=> #<SimpleForex::Currency:0x000000013c4bae78
 id: 1,
 blob:
  {"base"=>"USD",
   "rates"=>
    {"AED"=>"3.67286",
     "AFN"=>"89.49999",
     "ALL"=>"108.164235",
     "AMD"=>"388.147964",
     "ANG"=>"1.798456",
     "AOA"=>"503.891",
     "ARS"=>"198.1831",
     "AUD"=>"1.485125",

     ...
     
     "XOF"=>"617.115134",
     "XPD"=>"0.00069861",
     "XPF"=>"112.265627",
     "XPT"=>"0.00103175",
     "YER"=>"250.300106",
     "ZAR"=>"18.23512",
     "ZMW"=>"19.934751",
     "ZWL"=>"322.0"},
   "license"=>"https://openexchangerates.org/license",
   "timestamp"=>1678096800,
   "disclaimer"=>"Usage subject to terms: https://openexchangerates.org/terms"},
 created_at: Mon, 06 Mar 2023 10:43:54 UTC +00:00,
 updated_at: Mon, 06 Mar 2023 10:43:54 UTC +00:00>

Optional

Schedule the simple_forex:fetch_rates rake task to run at the frequency you require.

Tip: open exchange rates's free API gives 1000 calls monthly, and there are ~700 hours in month, so you safely run it hourly while staying within the free limit.

Convert currencies by calling

require 'simple_forex'
convert(amount, from_currency, to_currency)

Example

require 'simple_forex'
convert(100, 'USD', 'EUR')
# => 0.939717e2

Note ruby decimals use scientific notation, evidenced by the e toward the end of the value.

This gem probably only works on Rails 6 and Rails 7 apps, and only those using a postgres database.

Bug reports and pull requests are very welcome at https://github.com/stevecondylios/simple_forex.

The gem is available as open source under the terms of the MIT License.