JSON with Ruby – Encode, Decode, and Use JSON Easily (2025 Guide)

Introduction – Why Use JSON with Ruby?

JSON (JavaScript Object Notation) is a lightweight and popular format for storing and exchanging data across web services, APIs, and frontend-backend applications. Ruby includes built-in support for JSON through the json library, allowing developers to parse JSON strings, convert Ruby objects to JSON, and integrate with web APIs seamlessly.

In this guide, you’ll learn:

• How to encode/decode JSON in Ruby
• Handling JSON with hashes, arrays, and classes
• Reading from and writing to JSON files
• Best practices and real-world usage

Loading Ruby’s JSON Module

Before working with JSON, require the built-in module:

require 'json'

No extra gems are needed—json is included in Ruby’s standard library.

Encoding Ruby Objects to JSON

Example – Convert Hash to JSON

require 'json'

user = {
  name: "Alice",
  age: 30,
  email: "alice@example.com"
}

json_data = user.to_json
puts json_data

Output:

{"name":"Alice","age":30,"email":"alice@example.com"}

✔️ Use to_json on Ruby hashes and arrays
✔️ Automatically converts types like strings, numbers, booleans

Decoding JSON to Ruby Objects

Example – Parse JSON String into Hash

require 'json'

json_str = '{"name":"Bob","age":25,"admin":false}'
data = JSON.parse(json_str)

puts data["name"]  # Output: Bob

✔️ JSON.parse() converts JSON string into a Ruby hash or array

Reading and Writing JSON Files

Writing JSON to a File

require 'json'

user = { name: "Carol", age: 22 }

File.open("user.json", "w") do |f|
  f.write(user.to_json)
end

Reading JSON from a File

require 'json'

file = File.read("user.json")
data = JSON.parse(file)

puts data["age"]  # Output: 22

Working with Ruby Classes and JSON

Convert Object to JSON

require 'json'

class Product
  attr_accessor :name, :price

  def initialize(name, price)
    @name = name
    @price = price
  end

  def to_json(*_args)
    { name: @name, price: @price }.to_json
  end
end

item = Product.new("Laptop", 1299.99)
puts item.to_json

✔️ Custom to_json method allows JSON encoding for objects

Best Practices for JSON in Ruby

Useful JSON Options

JSON.parse(json_str, symbolize_names: true)

Converts keys from strings to symbols:
{"name" => "Alice"} → {name: "Alice"}

Summary – Recap & Next Steps

JSON support in Ruby is clean, fast, and part of the standard library—making it ideal for APIs, web apps, file storage, and integrations.

Key Takeaways:

• Use to_json to encode Ruby objects
• Use JSON.parse() to decode JSON strings
• Read/write JSON files using standard file methods
• Add custom serialization for Ruby classes

Real-world use:

Used in Rails APIs, configuration systems, HTTP clients, background workers, and frontend-backend sync.

FAQ – JSON with Ruby

How do I convert a Ruby hash to JSON?
Use hash.to_json.

How do I parse a JSON string into a Ruby object?
Use JSON.parse(json_string).

Can I parse JSON with symbolized keys in Ruby?
Yes, pass symbolize_names: true to JSON.parse.

Is JSON built into Ruby?
Yes. The json module is part of Ruby’s standard library—no gems needed.