[ruby-on-rails] How to "pretty" format JSON output in Ruby on Rails

I would like my JSON output in Ruby on Rails to be "pretty" or nicely formatted.

Right now, I call to_json and my JSON is all on one line. At times this can be difficult to see if there is a problem in the JSON output stream.

Is there way to configure to make my JSON "pretty" or nicely formatted in Rails?

If you're looking to quickly implement this in a Rails controller action to send a JSON response:

def index
  my_json = '{ "key": "value" }'
  render json: JSON.pretty_generate( JSON.parse my_json )
end

I have used the gem CodeRay and it works pretty well. The format includes colors and it recognises a lot of different formats.

I have used it on a gem that can be used for debugging rails APIs and it works pretty well.

By the way, the gem is named 'api_explorer' (http://www.github.com/toptierlabs/api_explorer)

Here's my solution which I derived from other posts during my own search.

This allows you to send the pp and jj output to a file as needed.

require "pp"
require "json"

class File
  def pp(*objs)
    objs.each {|obj|
      PP.pp(obj, self)
    }
    objs.size <= 1 ? objs.first : objs
  end
  def jj(*objs)
    objs.each {|obj|
      obj = JSON.parse(obj.to_json)
      self.puts JSON.pretty_generate(obj)
    }
    objs.size <= 1 ? objs.first : objs
  end
end

test_object = { :name => { first: "Christopher", last: "Mullins" }, :grades => [ "English" => "B+", "Algebra" => "A+" ] }

test_json_object = JSON.parse(test_object.to_json)

File.open("log/object_dump.txt", "w") do |file|
  file.pp(test_object)
end

File.open("log/json_dump.txt", "w") do |file|
  file.jj(test_json_object)
end

If you are using RABL you can configure it as described here to use JSON.pretty_generate:

class PrettyJson
  def self.dump(object)
    JSON.pretty_generate(object, {:indent => "  "})
  end
end

Rabl.configure do |config|
  ...
  config.json_engine = PrettyJson if Rails.env.development?
  ...
end

A problem with using JSON.pretty_generate is that JSON schema validators will no longer be happy with your datetime strings. You can fix those in your config/initializers/rabl_config.rb with:

ActiveSupport::TimeWithZone.class_eval do
  alias_method :orig_to_s, :to_s
  def to_s(format = :default)
    format == :default ? iso8601 : orig_to_s(format)
  end
end

The <pre> tag in HTML, used with JSON.pretty_generate, will render the JSON pretty in your view. I was so happy when my illustrious boss showed me this:

<% if @data.present? %>
   <pre><%= JSON.pretty_generate(@data) %></pre>
<% end %>

If you want to:

1. Prettify all outgoing JSON responses from your app automatically.
2. Avoid polluting Object#to_json/#as_json
3. Avoid parsing/re-rendering JSON using middleware (YUCK!)
4. Do it the RAILS WAY!

Then ... replace the ActionController::Renderer for JSON! Just add the following code to your ApplicationController:

ActionController::Renderers.add :json do |json, options|
  unless json.kind_of?(String)
    json = json.as_json(options) if json.respond_to?(:as_json)
    json = JSON.pretty_generate(json, options)
  end

  if options[:callback].present?
    self.content_type ||= Mime::JS
    "#{options[:callback]}(#{json})"
  else
    self.content_type ||= Mime::JSON
    json
  end
end

Using <pre> HTML code and pretty_generate is good trick:

<%
  require 'json'

  hash = JSON[{hey: "test", num: [{one: 1, two: 2, threes: [{three: 3, tthree: 33}]}]}.to_json] 
%>

<pre>
  <%=  JSON.pretty_generate(hash) %>
</pre>

Simplest example, I could think of:

my_json = '{ "name":"John", "age":30, "car":null }'
puts JSON.pretty_generate(JSON.parse(my_json))

Rails console example:

core dev 1555:0> my_json = '{ "name":"John", "age":30, "car":null }'
=> "{ \"name\":\"John\", \"age\":30, \"car\":null }"
core dev 1556:0> puts JSON.pretty_generate(JSON.parse(my_json))
{
  "name": "John",
  "age": 30,
  "car": null
}
=> nil

Here is a middleware solution modified from this excellent answer by @gertas. This solution is not Rails specific--it should work with any Rack application.

The middleware technique used here, using #each, is explained at ASCIIcasts 151: Rack Middleware by Eifion Bedford.

This code goes in app/middleware/pretty_json_response.rb:

class PrettyJsonResponse

  def initialize(app)
    @app = app
  end

  def call(env)
    @status, @headers, @response = @app.call(env)
    [@status, @headers, self]
  end

  def each(&block)
    @response.each do |body|
      if @headers["Content-Type"] =~ /^application\/json/
        body = pretty_print(body)
      end
      block.call(body)
    end
  end

  private

  def pretty_print(json)
    obj = JSON.parse(json)  
    JSON.pretty_unparse(obj)
  end

end

To turn it on, add this to config/environments/test.rb and config/environments/development.rb:

config.middleware.use "PrettyJsonResponse"

As @gertas warns in his version of this solution, avoid using it in production. It's somewhat slow.

Tested with Rails 4.1.6.

Thanks to Rack Middleware and Rails 3 you can output pretty JSON for every request without changing any controller of your app. I have written such middleware snippet and I get nicely printed JSON in browser and curl output.

class PrettyJsonResponse
  def initialize(app)
    @app = app
  end

  def call(env)
    status, headers, response = @app.call(env)
    if headers["Content-Type"] =~ /^application\/json/
      obj = JSON.parse(response.body)
      pretty_str = JSON.pretty_unparse(obj)
      response = [pretty_str]
      headers["Content-Length"] = pretty_str.bytesize.to_s
    end
    [status, headers, response]
  end
end

The above code should be placed in app/middleware/pretty_json_response.rb of your Rails project. And the final step is to register the middleware in config/environments/development.rb:

config.middleware.use PrettyJsonResponse

I don't recommend to use it in production.rb. The JSON reparsing may degrade response time and throughput of your production app. Eventually extra logic such as 'X-Pretty-Json: true' header may be introduced to trigger formatting for manual curl requests on demand.

(Tested with Rails 3.2.8-5.0.0, Ruby 1.9.3-2.2.0, Linux)

Dumping an ActiveRecord object to JSON (in the Rails console):

pp User.first.as_json

# => {
 "id" => 1,
 "first_name" => "Polar",
 "last_name" => "Bear"
}

Pretty print variant:

my_object = { :array => [1, 2, 3, { :sample => "hash"}, 44455, 677778, 9900 ], :foo => "bar", rrr: {"pid": 63, "state": false}}
puts my_object.as_json.pretty_inspect.gsub('=>', ': ')

Result:

{"array": [1, 2, 3, {"sample": "hash"}, 44455, 677778, 9900],
 "foo": "bar",
 "rrr": {"pid": 63, "state": false}}

Thanks to Rack Middleware and Rails 3 you can output pretty JSON for every request without changing any controller of your app. I have written such middleware snippet and I get nicely printed JSON in browser and curl output.

class PrettyJsonResponse
  def initialize(app)
    @app = app
  end

  def call(env)
    status, headers, response = @app.call(env)
    if headers["Content-Type"] =~ /^application\/json/
      obj = JSON.parse(response.body)
      pretty_str = JSON.pretty_unparse(obj)
      response = [pretty_str]
      headers["Content-Length"] = pretty_str.bytesize.to_s
    end
    [status, headers, response]
  end
end

The above code should be placed in app/middleware/pretty_json_response.rb of your Rails project. And the final step is to register the middleware in config/environments/development.rb:

config.middleware.use PrettyJsonResponse

I don't recommend to use it in production.rb. The JSON reparsing may degrade response time and throughput of your production app. Eventually extra logic such as 'X-Pretty-Json: true' header may be introduced to trigger formatting for manual curl requests on demand.

(Tested with Rails 3.2.8-5.0.0, Ruby 1.9.3-2.2.0, Linux)

# example of use:
a_hash = {user_info: {type: "query_service", e_mail: "[email protected]", phone: "+79876543322"}, cars_makers: ["bmw", "mitsubishi"], car_models: [bmw: {model: "1er", year_mfc: 2006}, mitsubishi: {model: "pajero", year_mfc: 1997}]}
pretty_html = a_hash.pretty_html

# include this module to your libs:
module MyPrettyPrint
    def pretty_html indent = 0
        result = ""
        if self.class == Hash
            self.each do |key, value|
                result += "#{key}
: #{[Array, Hash].include?(value.class) ? value.pretty_html(indent+1) : value}
"
            end
        elsif self.class == Array
            result = "[#{self.join(', ')}]"
        end
        "#{result}"
    end

end

class Hash
    include MyPrettyPrint
end

class Array
    include MyPrettyPrint
end

If you want to:

1. Prettify all outgoing JSON responses from your app automatically.
2. Avoid polluting Object#to_json/#as_json
3. Avoid parsing/re-rendering JSON using middleware (YUCK!)
4. Do it the RAILS WAY!

Then ... replace the ActionController::Renderer for JSON! Just add the following code to your ApplicationController:

ActionController::Renderers.add :json do |json, options|
  unless json.kind_of?(String)
    json = json.as_json(options) if json.respond_to?(:as_json)
    json = JSON.pretty_generate(json, options)
  end

  if options[:callback].present?
    self.content_type ||= Mime::JS
    "#{options[:callback]}(#{json})"
  else
    self.content_type ||= Mime::JSON
    json
  end
end

If you find that the pretty_generate option built into Ruby's JSON library is not "pretty" enough, I recommend my own NeatJSON gem for your formatting.

To use it:

gem install neatjson

and then use

JSON.neat_generate

instead of

JSON.pretty_generate

Like Ruby's pp it will keep objects and arrays on one line when they fit, but wrap to multiple as needed. For example:

{
  "navigation.createroute.poi":[
    {"text":"Lay in a course to the Hilton","params":{"poi":"Hilton"}},
    {"text":"Take me to the airport","params":{"poi":"airport"}},
    {"text":"Let's go to IHOP","params":{"poi":"IHOP"}},
    {"text":"Show me how to get to The Med","params":{"poi":"The Med"}},
    {"text":"Create a route to Arby's","params":{"poi":"Arby's"}},
    {
      "text":"Go to the Hilton by the Airport",
      "params":{"poi":"Hilton","location":"Airport"}
    },
    {
      "text":"Take me to the Fry's in Fresno",
      "params":{"poi":"Fry's","location":"Fresno"}
    }
  ],
  "navigation.eta":[
    {"text":"When will we get there?"},
    {"text":"When will I arrive?"},
    {"text":"What time will I get to the destination?"},
    {"text":"What time will I reach the destination?"},
    {"text":"What time will it be when I arrive?"}
  ]
}

It also supports a variety of formatting options to further customize your output. For example, how many spaces before/after colons? Before/after commas? Inside the brackets of arrays and objects? Do you want to sort the keys of your object? Do you want the colons to all be lined up?

Dumping an ActiveRecord object to JSON (in the Rails console):

pp User.first.as_json

# => {
 "id" => 1,
 "first_name" => "Polar",
 "last_name" => "Bear"
}

If you are using RABL you can configure it as described here to use JSON.pretty_generate:

class PrettyJson
  def self.dump(object)
    JSON.pretty_generate(object, {:indent => "  "})
  end
end

Rabl.configure do |config|
  ...
  config.json_engine = PrettyJson if Rails.env.development?
  ...
end

A problem with using JSON.pretty_generate is that JSON schema validators will no longer be happy with your datetime strings. You can fix those in your config/initializers/rabl_config.rb with:

ActiveSupport::TimeWithZone.class_eval do
  alias_method :orig_to_s, :to_s
  def to_s(format = :default)
    format == :default ? iso8601 : orig_to_s(format)
  end
end

# example of use:
a_hash = {user_info: {type: "query_service", e_mail: "[email protected]", phone: "+79876543322"}, cars_makers: ["bmw", "mitsubishi"], car_models: [bmw: {model: "1er", year_mfc: 2006}, mitsubishi: {model: "pajero", year_mfc: 1997}]}
pretty_html = a_hash.pretty_html

# include this module to your libs:
module MyPrettyPrint
    def pretty_html indent = 0
        result = ""
        if self.class == Hash
            self.each do |key, value|
                result += "#{key}
: #{[Array, Hash].include?(value.class) ? value.pretty_html(indent+1) : value}
"
            end
        elsif self.class == Array
            result = "[#{self.join(', ')}]"
        end
        "#{result}"
    end

end

class Hash
    include MyPrettyPrint
end

class Array
    include MyPrettyPrint
end

I have used the gem CodeRay and it works pretty well. The format includes colors and it recognises a lot of different formats.

I have used it on a gem that can be used for debugging rails APIs and it works pretty well.

By the way, the gem is named 'api_explorer' (http://www.github.com/toptierlabs/api_explorer)

If you find that the pretty_generate option built into Ruby's JSON library is not "pretty" enough, I recommend my own NeatJSON gem for your formatting.

To use it:

gem install neatjson

and then use

JSON.neat_generate

instead of

JSON.pretty_generate

Like Ruby's pp it will keep objects and arrays on one line when they fit, but wrap to multiple as needed. For example:

{
  "navigation.createroute.poi":[
    {"text":"Lay in a course to the Hilton","params":{"poi":"Hilton"}},
    {"text":"Take me to the airport","params":{"poi":"airport"}},
    {"text":"Let's go to IHOP","params":{"poi":"IHOP"}},
    {"text":"Show me how to get to The Med","params":{"poi":"The Med"}},
    {"text":"Create a route to Arby's","params":{"poi":"Arby's"}},
    {
      "text":"Go to the Hilton by the Airport",
      "params":{"poi":"Hilton","location":"Airport"}
    },
    {
      "text":"Take me to the Fry's in Fresno",
      "params":{"poi":"Fry's","location":"Fresno"}
    }
  ],
  "navigation.eta":[
    {"text":"When will we get there?"},
    {"text":"When will I arrive?"},
    {"text":"What time will I get to the destination?"},
    {"text":"What time will I reach the destination?"},
    {"text":"What time will it be when I arrive?"}
  ]
}

It also supports a variety of formatting options to further customize your output. For example, how many spaces before/after colons? Before/after commas? Inside the brackets of arrays and objects? Do you want to sort the keys of your object? Do you want the colons to all be lined up?

#At Controller
def branch
    @data = Model.all
    render json: JSON.pretty_generate(@data.as_json)
end

Using <pre> HTML code and pretty_generate is good trick:

<%
  require 'json'

  hash = JSON[{hey: "test", num: [{one: 1, two: 2, threes: [{three: 3, tthree: 33}]}]}.to_json] 
%>

<pre>
  <%=  JSON.pretty_generate(hash) %>
</pre>

Pretty print variant:

my_object = { :array => [1, 2, 3, { :sample => "hash"}, 44455, 677778, 9900 ], :foo => "bar", rrr: {"pid": 63, "state": false}}
puts my_object.as_json.pretty_inspect.gsub('=>', ': ')

Result:

{"array": [1, 2, 3, {"sample": "hash"}, 44455, 677778, 9900],
 "foo": "bar",
 "rrr": {"pid": 63, "state": false}}

Simplest example, I could think of:

my_json = '{ "name":"John", "age":30, "car":null }'
puts JSON.pretty_generate(JSON.parse(my_json))

Rails console example:

core dev 1555:0> my_json = '{ "name":"John", "age":30, "car":null }'
=> "{ \"name\":\"John\", \"age\":30, \"car\":null }"
core dev 1556:0> puts JSON.pretty_generate(JSON.parse(my_json))
{
  "name": "John",
  "age": 30,
  "car": null
}
=> nil

The <pre> tag in HTML, used with JSON.pretty_generate, will render the JSON pretty in your view. I was so happy when my illustrious boss showed me this:

<% if @data.present? %>
   <pre><%= JSON.pretty_generate(@data) %></pre>
<% end %>

Check out Awesome Print. Parse the JSON string into a Ruby Hash, then display it with ap like so:

require "awesome_print"
require "json"

json = '{"holy": ["nested", "json"], "batman!": {"a": 1, "b": 2}}'

ap(JSON.parse(json))

With the above, you'll see:

{
  "holy" => [
    [0] "nested",
    [1] "json"
  ],
  "batman!" => {
    "a" => 1,
    "b" => 2
  }
}

Awesome Print will also add some color that Stack Overflow won't show you.

If you're looking to quickly implement this in a Rails controller action to send a JSON response:

def index
  my_json = '{ "key": "value" }'
  render json: JSON.pretty_generate( JSON.parse my_json )
end

I use the following as I find the headers, status and JSON output useful as a set. The call routine is broken out on recommendation from a railscasts presentation at: http://railscasts.com/episodes/151-rack-middleware?autoplay=true

  class LogJson

  def initialize(app)
    @app = app
  end

  def call(env)
    dup._call(env)
  end

  def _call(env)
    @status, @headers, @response = @app.call(env)
    [@status, @headers, self]
  end

  def each(&block)
    if @headers["Content-Type"] =~ /^application\/json/
      obj = JSON.parse(@response.body)
      pretty_str = JSON.pretty_unparse(obj)
      @headers["Content-Length"] = Rack::Utils.bytesize(pretty_str).to_s
      Rails.logger.info ("HTTP Headers:  #{ @headers } ")
      Rails.logger.info ("HTTP Status:  #{ @status } ")
      Rails.logger.info ("JSON Response:  #{ pretty_str} ")
    end

    @response.each(&block)
  end
  end

#At Controller
def branch
    @data = Model.all
    render json: JSON.pretty_generate(@data.as_json)
end

I use the following as I find the headers, status and JSON output useful as a set. The call routine is broken out on recommendation from a railscasts presentation at: http://railscasts.com/episodes/151-rack-middleware?autoplay=true

  class LogJson

  def initialize(app)
    @app = app
  end

  def call(env)
    dup._call(env)
  end

  def _call(env)
    @status, @headers, @response = @app.call(env)
    [@status, @headers, self]
  end

  def each(&block)
    if @headers["Content-Type"] =~ /^application\/json/
      obj = JSON.parse(@response.body)
      pretty_str = JSON.pretty_unparse(obj)
      @headers["Content-Length"] = Rack::Utils.bytesize(pretty_str).to_s
      Rails.logger.info ("HTTP Headers:  #{ @headers } ")
      Rails.logger.info ("HTTP Status:  #{ @status } ")
      Rails.logger.info ("JSON Response:  #{ pretty_str} ")
    end

    @response.each(&block)
  end
  end

Here's my solution which I derived from other posts during my own search.

This allows you to send the pp and jj output to a file as needed.

require "pp"
require "json"

class File
  def pp(*objs)
    objs.each {|obj|
      PP.pp(obj, self)
    }
    objs.size <= 1 ? objs.first : objs
  end
  def jj(*objs)
    objs.each {|obj|
      obj = JSON.parse(obj.to_json)
      self.puts JSON.pretty_generate(obj)
    }
    objs.size <= 1 ? objs.first : objs
  end
end

test_object = { :name => { first: "Christopher", last: "Mullins" }, :grades => [ "English" => "B+", "Algebra" => "A+" ] }

test_json_object = JSON.parse(test_object.to_json)

File.open("log/object_dump.txt", "w") do |file|
  file.pp(test_object)
end

File.open("log/json_dump.txt", "w") do |file|
  file.jj(test_json_object)
end

Here is a middleware solution modified from this excellent answer by @gertas. This solution is not Rails specific--it should work with any Rack application.

The middleware technique used here, using #each, is explained at ASCIIcasts 151: Rack Middleware by Eifion Bedford.

This code goes in app/middleware/pretty_json_response.rb:

class PrettyJsonResponse

  def initialize(app)
    @app = app
  end

  def call(env)
    @status, @headers, @response = @app.call(env)
    [@status, @headers, self]
  end

  def each(&block)
    @response.each do |body|
      if @headers["Content-Type"] =~ /^application\/json/
        body = pretty_print(body)
      end
      block.call(body)
    end
  end

  private

  def pretty_print(json)
    obj = JSON.parse(json)  
    JSON.pretty_unparse(obj)
  end

end

To turn it on, add this to config/environments/test.rb and config/environments/development.rb:

config.middleware.use "PrettyJsonResponse"

As @gertas warns in his version of this solution, avoid using it in production. It's somewhat slow.

Tested with Rails 4.1.6.