Cookies are read and written through ActionController#cookies.

The cookies being read are the ones received along with the request, the cookies being written will be sent out with the response. Reading a cookie does not get the cookie object itself back, just the value it holds.

Examples of writing:

# Sets a simple session cookie.
# This cookie will be deleted when the user's browser is closed.
cookies[:user_name] = "david"

# Cookie values are String based. Other data types need to be serialized.
cookies[:lat_lon] = JSON.generate([47.68, -122.37])

# Sets a cookie that expires in 1 hour.
cookies[:login] = { value: "XJ-122", expires: 1.hour }

# Sets a cookie that expires at a specific time.
cookies[:login] = { value: "XJ-122", expires: Time.utc(2020, 10, 15, 5) }

# Sets a signed cookie, which prevents users from tampering with its value.
# It can be read using the signed method `cookies.signed[:name]`
cookies.signed[:user_id] =

# Sets an encrypted cookie value before sending it to the client which
# prevent users from reading and tampering with its value.
# It can be read using the encrypted method `cookies.encrypted[:name]`
cookies.encrypted[:discount] = 45

# Sets a "permanent" cookie (which expires in 20 years from now).
cookies.permanent[:login] = "XJ-122"

# You can also chain these methods:
cookies.signed.permanent[:login] = "XJ-122"

Examples of reading:

cookies[:user_name]           # => "david"
cookies.size                  # => 2
JSON.parse(cookies[:lat_lon]) # => [47.68, -122.37]
cookies.signed[:login]        # => "XJ-122"
cookies.encrypted[:discount]  # => 45

Example for deleting:

cookies.delete :user_name

Please note that if you specify a :domain when setting a cookie, you must also specify the domain when deleting the cookie:

cookies[:name] = {
  value: 'a yummy cookie',
  expires: 1.year,
  domain: ''

cookies.delete(:name, domain: '')

The option symbols for setting cookies are:

  • :value - The cookie's value.

  • :path - The path for which this cookie applies. Defaults to the root of the application.

  • :domain - The domain for which this cookie applies so you can restrict to the domain level. If you use a schema like and want to share session with set :domain to :all. Make sure to specify the :domain option with :all or Array again when deleting cookies.

    domain: nil  # Does not set cookie domain. (default)
    domain: :all # Allow the cookie for the top most level
                 # domain and subdomains.
    domain: %w( # Allow the cookie
                                          # for concrete domain names.
  • :tld_length - When using :domain => :all, this option can be used to explicitly set the TLD length when using a short (<= 3 character) domain that is being interpreted as part of a TLD. For example, to share cookies between and, set :tld_length to 2.

  • :expires - The time at which this cookie expires, as a Time or ActiveSupport::Duration object.

  • :secure - Whether this cookie is only transmitted to HTTPS servers. Default is false.

  • :httponly - Whether this cookie is accessible via scripting or only HTTP. Defaults to false.

AUTHENTICATED_ENCRYPTED_COOKIE_SALT = "action_dispatch.authenticated_encrypted_cookie_salt".freeze
COOKIES_DIGEST = "action_dispatch.cookies_digest".freeze
COOKIES_ROTATIONS = "action_dispatch.cookies_rotations".freeze
COOKIES_SERIALIZER = "action_dispatch.cookies_serializer".freeze
CookieOverflow = StandardError

Raised when storing more than 4K of session data.

ENCRYPTED_COOKIE_CIPHER = "action_dispatch.encrypted_cookie_cipher".freeze
ENCRYPTED_COOKIE_SALT = "action_dispatch.encrypted_cookie_salt".freeze
ENCRYPTED_SIGNED_COOKIE_SALT = "action_dispatch.encrypted_signed_cookie_salt".freeze
GENERATOR_KEY = "action_dispatch.key_generator".freeze
HTTP_HEADER = "Set-Cookie".freeze

Cookies can typically store 4096 bytes.

SECRET_KEY_BASE = "action_dispatch.secret_key_base".freeze
SECRET_TOKEN = "action_dispatch.secret_token".freeze
SIGNED_COOKIE_DIGEST = "action_dispatch.signed_cookie_digest".freeze
SIGNED_COOKIE_SALT = "action_dispatch.signed_cookie_salt".freeze
USE_AUTHENTICATED_COOKIE_ENCRYPTION = "action_dispatch.use_authenticated_cookie_encryption".freeze