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Have you ever needed to automatically convert JSON-style camelBack or CamelCase hash keys into more Rubyish snake_case?

Plissken to the rescue!

This gem recursively converts all camelBack or CamelCase keys in either a Hash structure, or an Array of Hashes, to snake_case.


  • Ruby >= 2.7


Add this to your Gemfile:

gem "plissken"

Or install it yourself as:

gem install plissken


On hashes:

my_hash = { "firstKey" => 1, "fooBars" => [{ "bazBaz" => "value" }, { "blahBlah" => "value" }] }
snaked_hash = my_hash.to_snake_keys
# => { "first_key" => 1, "foo_bars" => [{ "baz_baz" => "value" }, { "blah_blah" => "value" }] }

On arrays:

my_array_of_hashes = [{ "firstKey" => 1, "fooBars" => [{ "bazBaz" => "value" }, { "blahBlah" => "value" }] }]
snaked_hash = my_array_of_hashes.to_snake_keys
# => [{"first_key" => 1, "foo_bars" => [{ "baz_baz" => "value" }, { "blah_blah" => "value" }] }]

Plissken works on either string keys or symbolized keys. It has no dependencies, as it has its own underscore method lifted out of ActiveSupport.


  • Your keys must be camelBack or CamelCase. The key "Foo Bar" will output as "foo bar".
  • Unlike the original Snake Plissken in the seminal film Escape from New York, the plissken gem is non-destructive. There is no Hash#to_snake_keys! form.

Going the other way

If you've already got snake_case and need to CamelCase it, you are encouraged to try the Awrence gem.


Bug reports and pull requests are welcome on GitHub at This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.


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

Code of Conduct

Everyone interacting with this project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.