Base64 Encoding & Decoding in Ruby

Ruby's standard library includes a Base64 module with three encoding methods. The most important thing to know: encode64 adds newlines, but strict_encode64 does not — always use the strict variant for general use.

Basic Usage

require 'base64'

# Encode
encoded = Base64.strict_encode64("Hello, world!")
puts encoded  # "SGVsbG8sIHdvcmxkIQ=="

# Decode
decoded = Base64.strict_decode64("SGVsbG8sIHdvcmxkIQ==")
puts decoded  # "Hello, world!"

The Three Encoding Methods

Ruby's Base64 module provides three encoding methods — and they produce different output:

require 'base64'

data = "Hello, world!"

# encode64: adds a newline (\n) every 60 characters
Base64.encode64(data)
# => "SGVsbG8sIHdvcmxkIQ==\n"   ← has trailing newline!

# strict_encode64: RFC 4648 compliant, NO newlines
Base64.strict_encode64(data)
# => "SGVsbG8sIHdvcmxkIQ=="     ← clean

# urlsafe_encode64: URL-safe (-/_), NO padding by default
Base64.urlsafe_encode64(data)
# => "SGVsbG8sIHdvcmxkIQ=="    (padding optional)

URL-Safe Base64

require 'base64'

data = "data for a URL: a+b/c=d"

# Encode URL-safe (padding=true by default in Ruby 3.x)
encoded = Base64.urlsafe_encode64(data, padding: false)
puts encoded  # No +, /, or = characters

# Decode URL-safe
decoded = Base64.urlsafe_decode64(encoded)
puts decoded  # "data for a URL: a+b/c=d"

Encoding Files

require 'base64'

# Encode file to Base64 string
encoded = Base64.strict_encode64(File.binread("image.png"))
File.write("image.b64", encoded)

# Decode Base64 back to file
decoded = Base64.strict_decode64(File.read("image.b64"))
File.binwrite("output.png", decoded)

Creating Data URIs

require 'base64'
require 'mime/types'

def file_to_data_uri(path)
  mime = MIME::Types.type_for(path).first&.content_type || 'application/octet-stream'
  encoded = Base64.strict_encode64(File.binread(path))
  "data:#{mime};base64,#{encoded}"
end

puts file_to_data_uri("logo.png")
# "data:image/png;base64,iVBORw0KGgo..."

Decoding Methods

require 'base64'

encoded = "SGVsbG8sIHdvcmxkIQ=="

# decode64: handles newlines in input (lenient)
Base64.decode64(encoded)

# strict_decode64: strict RFC 4648, raises on invalid chars
begin
  Base64.strict_decode64(encoded)
rescue ArgumentError => e
  puts "Invalid Base64: #{e.message}"
end

# urlsafe_decode64: handles - and _ instead of + and /
Base64.urlsafe_decode64("SGVsbG8sIHdvcmxkIQ")

Rails / ActiveSupport

If you're in a Rails project, ActiveSupport extends Base64 with convenience methods:

require 'active_support/core_ext/string/encoding'

# Available via ActiveSupport::Base64
encoded = ::Base64.strict_encode64("Hello")

# Or for URL-safe tokens in Rails:
token = SecureRandom.base64(32)  # URL-safe random token