If you've worked with the rails encrypted credentials system before, you're probably familiar with the command to edit them
This will create(if it doesn't exist
config/credentials.yml.enc by way of the RAILS_MASTER_KEY). If you only have this credentials file, the items in this file will be available to all environments of your application.
But you can also create/edit environment specific credentials by specifying an environment. This will similarly create 2 files -
bin/rails credentials:edit --environment development
Credentials specified in this file will only be available in the development environment