diff --git a/app/controllers/api/v1/accounts_controller.rb b/app/controllers/api/v1/accounts_controller.rb
index ddb94d5ca48..653529316fb 100644
--- a/app/controllers/api/v1/accounts_controller.rb
+++ b/app/controllers/api/v1/accounts_controller.rb
@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 class Api::V1::AccountsController < Api::BaseController
+  include RegistrationHelper
+
   before_action -> { authorize_if_got_token! :read, :'read:accounts' }, except: [:create, :follow, :unfollow, :remove_from_followers, :block, :unblock, :mute, :unmute]
   before_action -> { doorkeeper_authorize! :follow, :write, :'write:follows' }, only: [:follow, :unfollow, :remove_from_followers]
   before_action -> { doorkeeper_authorize! :follow, :write, :'write:mutes' }, only: [:mute, :unmute]
@@ -90,18 +92,14 @@ class Api::V1::AccountsController < Api::BaseController
   end
 
   def account_params
-    params.permit(:username, :email, :password, :agreement, :locale, :reason, :time_zone)
+    params.permit(:username, :email, :password, :agreement, :locale, :reason, :time_zone, :invite_code)
+  end
+
+  def invite
+    Invite.find_by(code: params[:invite_code]) if params[:invite_code].present?
   end
 
   def check_enabled_registrations
-    forbidden if single_user_mode? || omniauth_only? || !allowed_registrations?
-  end
-
-  def allowed_registrations?
-    Setting.registrations_mode != 'none'
-  end
-
-  def omniauth_only?
-    ENV['OMNIAUTH_ONLY'] == 'true'
+    forbidden unless allowed_registration?(request.remote_ip, invite)
   end
 end
diff --git a/app/controllers/api/v1/invites_controller.rb b/app/controllers/api/v1/invites_controller.rb
new file mode 100644
index 00000000000..ea17ba74038
--- /dev/null
+++ b/app/controllers/api/v1/invites_controller.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+class Api::V1::InvitesController < Api::BaseController
+  include RegistrationHelper
+
+  skip_before_action :require_authenticated_user!
+  skip_around_action :set_locale
+
+  before_action :set_invite
+  before_action :check_enabled_registrations!
+
+  # Override `current_user` to avoid reading session cookies
+  def current_user; end
+
+  def show
+    render json: { invite_code: params[:invite_code], instance_api_url: api_v2_instance_url }, status: 200
+  end
+
+  private
+
+  def set_invite
+    @invite = Invite.find_by!(code: params[:invite_code])
+  end
+
+  def check_enabled_registrations!
+    return render json: { error: I18n.t('invites.invalid') }, status: 401 unless @invite.valid_for_use?
+
+    raise Mastodon::NotPermittedError unless allowed_registration?(request.remote_ip, @invite)
+  end
+end
diff --git a/app/controllers/auth/registrations_controller.rb b/app/controllers/auth/registrations_controller.rb
index 331484f36dc..8be7c5f192f 100644
--- a/app/controllers/auth/registrations_controller.rb
+++ b/app/controllers/auth/registrations_controller.rb
@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 class Auth::RegistrationsController < Devise::RegistrationsController
+  include RegistrationHelper
   include RegistrationSpamConcern
 
   layout :determine_layout
@@ -82,19 +83,7 @@ class Auth::RegistrationsController < Devise::RegistrationsController
   end
 
   def check_enabled_registrations
-    redirect_to root_path if single_user_mode? || omniauth_only? || !allowed_registrations? || ip_blocked?
-  end
-
-  def allowed_registrations?
-    Setting.registrations_mode != 'none' || @invite&.valid_for_use?
-  end
-
-  def omniauth_only?
-    ENV['OMNIAUTH_ONLY'] == 'true'
-  end
-
-  def ip_blocked?
-    IpBlock.where(severity: :sign_up_block).where('ip >>= ?', request.remote_ip.to_s).exists?
+    redirect_to root_path unless allowed_registration?(request.remote_ip, @invite)
   end
 
   def invite_code
diff --git a/app/helpers/registration_helper.rb b/app/helpers/registration_helper.rb
new file mode 100644
index 00000000000..ef5462ac887
--- /dev/null
+++ b/app/helpers/registration_helper.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+module RegistrationHelper
+  extend ActiveSupport::Concern
+
+  def allowed_registration?(remote_ip, invite)
+    !Rails.configuration.x.single_user_mode && !omniauth_only? && (registrations_open? || invite&.valid_for_use?) && !ip_blocked?(remote_ip)
+  end
+
+  def registrations_open?
+    Setting.registrations_mode != 'none'
+  end
+
+  def omniauth_only?
+    ENV['OMNIAUTH_ONLY'] == 'true'
+  end
+
+  def ip_blocked?(remote_ip)
+    IpBlock.where(severity: :sign_up_block).exists?(['ip >>= ?', remote_ip.to_s])
+  end
+end
diff --git a/app/services/app_sign_up_service.rb b/app/services/app_sign_up_service.rb
index 94547b61b21..76658801157 100644
--- a/app/services/app_sign_up_service.rb
+++ b/app/services/app_sign_up_service.rb
@@ -1,12 +1,14 @@
 # frozen_string_literal: true
 
 class AppSignUpService < BaseService
+  include RegistrationHelper
+
   def call(app, remote_ip, params)
     @app       = app
     @remote_ip = remote_ip
     @params    = params
 
-    raise Mastodon::NotPermittedError unless allowed_registrations?
+    raise Mastodon::NotPermittedError unless allowed_registration?(remote_ip, invite)
 
     ApplicationRecord.transaction do
       create_user!
@@ -34,8 +36,12 @@ class AppSignUpService < BaseService
     )
   end
 
+  def invite
+    Invite.find_by(code: @params[:invite_code]) if @params[:invite_code].present?
+  end
+
   def user_params
-    @params.slice(:email, :password, :agreement, :locale, :time_zone)
+    @params.slice(:email, :password, :agreement, :locale, :time_zone, :invite_code)
   end
 
   def account_params
@@ -45,24 +51,4 @@ class AppSignUpService < BaseService
   def invite_request_params
     { text: @params[:reason] }
   end
-
-  def allowed_registrations?
-    registrations_open? && !single_user_mode? && !omniauth_only? && !ip_blocked?
-  end
-
-  def registrations_open?
-    Setting.registrations_mode != 'none'
-  end
-
-  def single_user_mode?
-    Rails.configuration.x.single_user_mode
-  end
-
-  def omniauth_only?
-    ENV['OMNIAUTH_ONLY'] == 'true'
-  end
-
-  def ip_blocked?
-    IpBlock.where(severity: :sign_up_block).where('ip >>= ?', @remote_ip.to_s).exists?
-  end
 end
diff --git a/config/locales/en.yml b/config/locales/en.yml
index c298c47d351..7319de53dba 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -1368,6 +1368,7 @@ en:
       '86400': 1 day
     expires_in_prompt: Never
     generate: Generate invite link
+    invalid: This invite is not valid
     invited_by: 'You were invited by:'
     max_uses:
       one: 1 use
diff --git a/config/routes.rb b/config/routes.rb
index 3adda3b8224..82431f6ec3f 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -81,6 +81,8 @@ Rails.application.routes.draw do
     resource :outbox, only: [:show], module: :activitypub
   end
 
+  get '/invite/:invite_code', constraints: ->(req) { req.format == :json }, to: 'api/v1/invites#show'
+
   devise_scope :user do
     get '/invite/:invite_code', to: 'auth/registrations#new', as: :public_invite
 
diff --git a/spec/requests/invite_spec.rb b/spec/requests/invite_spec.rb
new file mode 100644
index 00000000000..c44ef2419c0
--- /dev/null
+++ b/spec/requests/invite_spec.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe 'invites' do
+  let(:invite) { Fabricate(:invite) }
+
+  context 'when requesting a JSON document' do
+    it 'returns a JSON document with expected attributes' do
+      get "/invite/#{invite.code}", headers: { 'Accept' => 'application/activity+json' }
+
+      expect(response).to have_http_status(200)
+      expect(response.media_type).to eq 'application/json'
+
+      expect(body_as_json[:invite_code]).to eq invite.code
+    end
+  end
+
+  context 'when not requesting a JSON document' do
+    it 'returns an HTML page' do
+      get "/invite/#{invite.code}"
+
+      expect(response).to have_http_status(200)
+      expect(response.media_type).to eq 'text/html'
+    end
+  end
+end
diff --git a/spec/services/app_sign_up_service_spec.rb b/spec/services/app_sign_up_service_spec.rb
index 2532304964c..d5946cf9b02 100644
--- a/spec/services/app_sign_up_service_spec.rb
+++ b/spec/services/app_sign_up_service_spec.rb
@@ -10,46 +10,72 @@ RSpec.describe AppSignUpService, type: :service do
   let(:remote_ip) { IPAddr.new('198.0.2.1') }
 
   describe '#call' do
-    it 'returns nil when registrations are closed' do
-      tmp = Setting.registrations_mode
-      Setting.registrations_mode = 'none'
-      expect { subject.call(app, remote_ip, good_params) }.to raise_error Mastodon::NotPermittedError
-      Setting.registrations_mode = tmp
+    let(:params) { good_params }
+
+    shared_examples 'successful registration' do
+      it 'creates an unconfirmed user with access token and the app\'s scope', :aggregate_failures do
+        access_token = subject.call(app, remote_ip, params)
+        expect(access_token).to_not be_nil
+        expect(access_token.scopes.to_s).to eq 'read write'
+
+        user = User.find_by(id: access_token.resource_owner_id)
+        expect(user).to_not be_nil
+        expect(user.confirmed?).to be false
+
+        expect(user.account).to_not be_nil
+        expect(user.invite_request).to be_nil
+      end
+    end
+
+    context 'when registrations are closed' do
+      around do |example|
+        tmp = Setting.registrations_mode
+        Setting.registrations_mode = 'none'
+
+        example.run
+
+        Setting.registrations_mode = tmp
+      end
+
+      it 'raises an error', :aggregate_failures do
+        expect { subject.call(app, remote_ip, good_params) }.to raise_error Mastodon::NotPermittedError
+      end
+
+      context 'when using a valid invite' do
+        let(:params) { good_params.merge({ invite_code: invite.code }) }
+        let(:invite) { Fabricate(:invite) }
+
+        before do
+          invite.user.approve!
+        end
+
+        it_behaves_like 'successful registration'
+      end
+
+      context 'when using an invalid invite' do
+        let(:params) { good_params.merge({ invite_code: invite.code }) }
+        let(:invite) { Fabricate(:invite, uses: 1, max_uses: 1) }
+
+        it 'raises an error', :aggregate_failures do
+          expect { subject.call(app, remote_ip, params) }.to raise_error Mastodon::NotPermittedError
+        end
+      end
     end
 
     it 'raises an error when params are missing' do
       expect { subject.call(app, remote_ip, {}) }.to raise_error ActiveRecord::RecordInvalid
     end
 
-    it 'creates an unconfirmed user with access token' do
-      access_token = subject.call(app, remote_ip, good_params)
-      expect(access_token).to_not be_nil
-      user = User.find_by(id: access_token.resource_owner_id)
-      expect(user).to_not be_nil
-      expect(user.confirmed?).to be false
-    end
+    it_behaves_like 'successful registration'
 
-    it 'creates access token with the app\'s scopes' do
-      access_token = subject.call(app, remote_ip, good_params)
-      expect(access_token).to_not be_nil
-      expect(access_token.scopes.to_s).to eq 'read write'
-    end
-
-    it 'creates an account' do
-      access_token = subject.call(app, remote_ip, good_params)
-      expect(access_token).to_not be_nil
-      user = User.find_by(id: access_token.resource_owner_id)
-      expect(user).to_not be_nil
-      expect(user.account).to_not be_nil
-      expect(user.invite_request).to be_nil
-    end
-
-    it 'creates an account with invite request text' do
-      access_token = subject.call(app, remote_ip, good_params.merge(reason: 'Foo bar'))
-      expect(access_token).to_not be_nil
-      user = User.find_by(id: access_token.resource_owner_id)
-      expect(user).to_not be_nil
-      expect(user.invite_request&.text).to eq 'Foo bar'
+    context 'when given an invite request text' do
+      it 'creates an account with invite request text' do
+        access_token = subject.call(app, remote_ip, good_params.merge(reason: 'Foo bar'))
+        expect(access_token).to_not be_nil
+        user = User.find_by(id: access_token.resource_owner_id)
+        expect(user).to_not be_nil
+        expect(user.invite_request&.text).to eq 'Foo bar'
+      end
     end
   end
 end