diff --git a/scripts/testflight-testers.rb b/scripts/testflight-testers.rb
new file mode 100755
index 0000000..ee6fe7e
--- /dev/null
+++ b/scripts/testflight-testers.rb
@@ -0,0 +1,60 @@
+#!/usr/bin/env ruby
+# Invite people to a TestFlight group.
+#
+#   APPLE_EMAIL=you@example.com ruby scripts/testflight-testers.rb someone@example.com ...
+#
+# Addresses come from the command line rather than a file in the repo, because a list of testers is
+# a list of people's email addresses and this repository is public.
+#
+# GROUP defaults to the external group, since the internal one only accepts people who already have
+# an App Store Connect account on the team, which is a far bigger thing to hand out than a build.
+begin
+  require "spaceship"
+rescue LoadError
+  libexec = Dir["/opt/homebrew/Cellar/fastlane/*/libexec", "/usr/local/Cellar/fastlane/*/libexec"].max
+  abort "spaceship is not installed. `brew install fastlane` and rerun." unless libexec
+  ENV["GEM_PATH"] = [libexec, ENV["GEM_PATH"]].compact.join(":")
+  Gem.clear_paths
+  require "spaceship"
+end
+
+BUNDLE_ID = ENV.fetch("BUNDLE_ID", "studio.margin.app")
+GROUP = ENV.fetch("GROUP", "Public Beta")
+ENV["FASTLANE_ITC_TEAM_ID"] = ENV.fetch("FASTLANE_ITC_TEAM_ID", "129377371")
+
+emails = ARGV.reject { |a| a.start_with?("-") }
+abort "Usage: ruby scripts/testflight-testers.rb someone@example.com [more@example.com ...]" if emails.empty?
+
+Spaceship::ConnectAPI.login(ENV["APPLE_EMAIL"], nil, use_portal: false, use_tunes: true)
+
+app = Spaceship::ConnectAPI::App.find(BUNDLE_ID)
+abort "No app for #{BUNDLE_ID}." unless app
+
+group = app.get_beta_groups.find { |g| g.name == GROUP }
+abort "No group named #{GROUP.inspect}." unless group
+puts "#{app.name}: #{group.name} (#{group.is_internal_group ? 'internal' : 'external'})"
+
+existing = Spaceship::ConnectAPI::BetaTester
+  .all(filter: { betaGroups: group.id })
+  .map { |t| t.email.to_s.downcase }
+
+emails.each do |email|
+  if existing.include?(email.downcase)
+    puts "  #{email} is already in this group"
+    next
+  end
+
+  Spaceship::ConnectAPI.post_bulk_beta_tester_assignments(
+    beta_group_id: group.id,
+    beta_testers: [{ email: email }],
+  )
+  puts "  invited #{email}"
+end
+
+puts
+if group.is_internal_group
+  puts "Internal testers can install as soon as a build finishes processing."
+else
+  puts "External testers get the invitation once beta app review passes."
+  puts "Anyone can also join through #{group.public_link}" if group.public_link
+end