Created: 2011-07-11 02:25
Updated: 2018-06-22 15:41
License: mit


Jsonify — a builder for JSON Build Status

Jsonify is to JSON as Builder is to XML.

To use Jsonify for Rails templates, install Jsonify-Rails.


Jsonify provides a builder style engine for creating correct JSON representations of Ruby objects entirely based on the JSON specification.


JSON and XML are the most common data representation formats used by RESTful applications. Jsonify is built on the belief that these representations belong in the view layer of the application.

Jsonify also seeks to emulate the simplicity of Builder. I have not found a single builder engine for JSON that provides a Builder-like experience. Jsonify is my attempt to remedy that situation.


Rails made XML generation easy with support for Builder templates, but, for JSON, there was no clear approach. (Note: Rails has since extracted jbuilder.)

For many applications, particularly those based on legacy a database, it is common to expose the data in a more client-friendly format than what is generated by the default Rails to_json method.

See Also

There are a number of related libraries available that try to solve this problem. Some of which take a similar approach to Jsonify and provide a builder-style interface. Others allow the developer to specify the representation using a common DSL that can generate both JSON and XML. Please take a look at these projects and consider your alternatives. It's my opinion that there are substantial and inherent differences between XML and JSON; and that these differences may force the developer to make concessions in one interface or the other.


gem install jsonify


Note: JSON output is usually shown "prettified" in examples. This is only for illustration purposes, as the Jsonify default is plain compact string without newlines. Enable pretty output by passing :format => :pretty to the Jsonify::Builder constructor. Keep in mind that pretty printing is a relatively costly operation so use it only when neccessary.

Compatibility Warning


Array handling was changed in 0.2.0 to provide a more natural feel. Code written using earlier versions of Jsonify may not work correctly. Previously you had to switch to a more conventional Ruby style for arrays:

json.links(@links) do |link|
  {:rel => link.type, :href => link.url}

This syntax was a frequent stumbling block with users. The interface for handling arrays is now consistent with the builder-style and should be less surprising:

json.links(@links) do |link|
  json.rel link.type
  json.href link.url

As always, all feedback is greatly appreciated. I want to know how this new style works out.

Quick Example

Using Jsonify to create some objects to represent a person and associated hyperlinks:

@person = Struct.new(:first_name,:last_name).new('George','Burdell')

Link = Struct.new(:type, :url)

@links = [
  Link.new('self', 'http://example.com/people/123'),
  Link.new('school', 'http://gatech.edu')

# Build this information as JSON
require 'jsonify'
json = Jsonify::Builder.new(:format => :pretty)

# Representation of the person
json.alumnus do
  json.fname @person.first_name
  json.lname @person.last_name

# Relevant links
json.links(@links) do |link|
  json.rel link.type
  json.href link.url

# Evaluate the result to a string

Gives you this JSON:

    "alumnus": {
        "fname": "George",
        "lname": "Burdell"
    "links": [
         "rel": "self",
         "href": "http://example.com/people/123"
        "rel": "school",
        "href": "http://gatech.edu"

Convenience methods

Jsonify provides class-level convenience methods that save you the trouble of instantiating the Jsonify::Builder. Each of these methods accepts a block, yields a new Builder object to the block, and then compiles the result.

  • compile
    • Compiles the given block; any options are passed to the instantiated Builder.
  • pretty
    • Compiles the given block; results are output in pretty format.
  • plain
    • Compiles the given block; results are output in plain (default) format.
Jsonify::Builder.plain do |j|
  j.song 'Fearless'
  j.album 'Meddle'

Rails View Templates

Jsonify can be used for Rails 3 view templates via the jsonify-rails which includes a Rails 3 template handler. Any template with a .jsonify extension will be handled by Rails.

The Jsonify template handler exposes the Jsonify::Builder instance to your template with the json variable:

json.hello do
  json.world "Jsonify is Working!"

Your Jsonify template will have access to any instance variables that are exposed through the controller. See Jsonify-Rails for additional details.


Jsonify views can use other Jsonify partials. How the template uses a partial depends on the returned string. Remember that partials always return strings as their results.

Jsonify partials

Jsonify partials are files that have a .jsonify extension. Partials must return a valid JSON string. The string should represent a JSON object (wrapped in curly braces {}) or a JSON array (wrapped in square brackets []).

Use the ingest! method to use a partial in your template:

json.ingest! (render :partial => 'my_partial')

ingest! parses the JSON into a Jsonify object graph, and then adds it to the builder.

In your main template:

# index.jsonify

json << 1
json.ingest! (render :partial => 'my_partial')

The first line creates an array using the append << operator. The second line shows how the partial is used. You cannot simply place render :partial ... on a line by itself as you can do with other templates like erb and haml. You have to explicitly tell Jsonify to add it to the builder.

Here's a partial:

# _my_partial.jsonify

json << 3
json << 4

This json variable in this partial is a separate distinct Jsonify::Builder instance from the json variable in the main template.

Wishlist: Figure out if a the json instance can be passed to the Jsonify partial to make things easier.

The partial returns:


Now, combining our index and partial we get:

Other partials

You can also use output from non-Jsonify templates (e.g. erb); just remember that the output from a template is always a string and that you have to tell the builder how to include the result of the partial.

Given an ERB partial:

<!-- _today.erb --> 
<%= Date.today %>

and you use it in a Jsonify template:

json << 1
json << { :date => (render :partial => 'today') }

You get:


Tilt Integration

Jsonify includes support for Tilt. This allow you to create views that use Jsonify with any framework that supports Tilt. Here's an example of a simple Sinatra application that leverages Jsonify's Tilt integration:

require 'bundler/setup'
require 'sinatra'

require 'jsonify'
require 'jsonify/tilt'

helpers do
  def jsonify(*args) 
    render(:jsonify, *args) 

get '/' do
  jsonify :index

And the corresponding template in views\index.jsonify

json.hello :frank

Usage Patterns


As mentioned before, Jsonify is designed to support construction of valid JSON and is entirely based on the JSON specification.

JSON is built on two fundamental structures:

  • object: a collection of name-value pairs -- in Jsonify this is a JsonObject
  • array: an ordered list of values -- in Jsonify this is a JsonArray

Jsonify adheres to the JSON specification and provides explicit support for working with these primary structures. A JSON string must be one of these structures and Jsonify ensures that this condition is met.

Creating JSON Objects

A JSON object, sometimes referred to as an object literal, is a common structure familiar to most developers. It's analogous to the nested element structure common in XML. The JSON RFC states that "the names within an object SHOULD be unique". Jsonify enforces this recommendation by backing the JsonObject with a Hash; an object that must have unique keys and the last one in, wins.

json = Jsonify::Builder.new
json.person do # start a new JsonObject where the key is 'foo'
  json.name 'George Burdell' # add a pair to this object
  json.skills ['engineering','bombing'] # adds a pair with an array value
  json.name 'George P. Burdell'
    "person": {
        "name": "George P. Burdell",
        "skills": [

It's perfectly legitimate for a JSON representation to simply be a collection of name-value pairs without a root element. Jsonify supports this by allowing you to specify the pairs that make up the object.

json = Jsonify::Builder.new
json.location 'Library Coffeehouse'
json.neighborhood 'Brookhaven'
    "location": "Library Coffeehouse",
    "neighborhood": "Brookhaven"

If the name you want contains whitespace or other characters not allowed in a Ruby method name, use tag!.

json.tag!("my location", 'Library Coffeehouse')
json.neighborhood 'Brookhaven'
    "my location": "Library Coffeehouse",
    "neighborhood": "Brookhaven"

Jsonify also supports a hash-style interface for creating objects:

json = Jsonify::Builder.new
json[:foo] = :bar
json[:go]  = :far
    "foo": "bar",
    "go": "far"

Use the hash-style within a block as well:

json.homer do
  json[:beer] = "Duffs"
  json[:spouse] = "Marge"
    "homer": {
        "beer": "Duffs",
        "spouse": "Marge"

Use store! for a more method-based style:

json.store!(:foo, :bar)
json.store!(:go, :far)

Creating JSON Arrays

A JSON array is an ordered list of JSON values. A JSON value can be a simple value, like a string or a number, or a supported JavaScript primitive like true, false, or null. A JSON value can also be a JSON object or another JSON array. Jsonify strives to make this kind of construction possible in a buider-style.

Jsonify supports JSON array construction through two approaches: method_missing and append!.

Use method_missing

Pass an array and a block to method_missing (or tag!), and Jsonify will create a JSON array. It will then iterate over the array and call the block for each item in the array. Use the json object within the block to add items to the JSON array.

That JSON array is then set as the value of the name-value pair, where the name comes from the method name (for method_missing) or symbol (for tag!).

This construct creates a JSON pair and a JSON array as the value of the pair.

Jsonify::Builder.pretty do |json|
  json.letters('a'..'c') do |letter|
    json << letter.upcase
    "letters": [

Another way to handle this particular example is to get rid of the block entirely. Simply pass the array directly:

json.letters ('a'..'c').map(&:upcase)
Use append!

Use this method and the builder will assume you are adding values to a JSON array without the surrounding object.

  • Use append! for multiple values
  • Use << for a single value

Multiple values:

json = Jsonify::Builder.new
json.append! 'a'.upcase, 'b'.upcase, 'c'.upcase

or more idiomatically:

json.append! *('a'..'c').map(&:upcase)

Single values:

json << 'a'.upcase
json << 'b'.upcase
json << 'c'.upcase

Standard iteration works here:

json = Jsonify::Builder.new
('a'..'c').each do |letter|
  json << letter.upcase

Mixing JSON Arrays and Objects

You can readily mix JSON arrays and objects and the Jsonify builder will do its best to keep things straight.

Start with an array and add an object:

json = Jsonify::Builder.new
json.append! 1,2,3
json.say "go, cat go"
[1,2,3,{"say":"go, cat go"}]

The builder sees the name-value pair being added to an array and converts it to a JSON object.

Now, start with an object and add an array:

json.foo 'bar'
json.go  'far'
json  << 'baz'

The builder now sees the single item (baz) and turns it into a name-value pair with a null value.


Yard Docs

Related Projects


This project is released under the MIT license.


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