diff --git a/Gemfile b/Gemfile
index 5795448..be260aa 100644
--- a/Gemfile
+++ b/Gemfile
@@ -11,6 +11,7 @@ group :development do
   gem 'html2rss-generator', github: 'html2rss/generator', branch: :main
 
   gem 'nokogiri'
+  gem 'public_suffix'
   gem 'rspec', '~> 3.0'
   gem 'rubocop'
   gem 'rubocop-performance'
diff --git a/Gemfile.lock b/Gemfile.lock
index 7017eb5..aa39ddd 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -111,8 +111,12 @@ GEM
       logger
       mime-types-data (~> 3.2025, >= 3.2025.0507)
     mime-types-data (3.2025.0924)
+    mini_portile2 (2.8.9)
     net-http (0.9.1)
       uri (>= 0.11.1)
+    nokogiri (1.18.8)
+      mini_portile2 (~> 2.8.2)
+      racc (~> 1.4)
     nokogiri (1.18.8-arm64-darwin)
       racc (~> 1.4)
     nokogiri (1.18.8-x86_64-darwin)
@@ -225,6 +229,7 @@ DEPENDENCIES
   html2rss-configs!
   html2rss-generator!
   nokogiri
+  public_suffix
   rspec (~> 3.0)
   rubocop
   rubocop-performance
diff --git a/README.md b/README.md
index ed18d98..9610a96 100644
--- a/README.md
+++ b/README.md
@@ -57,6 +57,8 @@ make test-domain DOMAIN=github.com
 
 **Adding new configs**: Just create the YAML file and run tests. No spec file needed.
 
+**Config folder convention**: Place configs under the registrable domain folder (e.g., `example.com/` or `bbc.co.uk/`). Legacy subdomain folders (e.g., `news.example.com/`) are allowed but not preferred.
+
 ## Documentation
 
 - [Main Documentation](https://html2rss.github.io/html2rss-configs/)
diff --git a/spec/helper_spec.rb b/spec/helper_spec.rb
new file mode 100644
index 0000000..05527c1
--- /dev/null
+++ b/spec/helper_spec.rb
@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+RSpec.describe Helper do
+  describe '.url_to_registrable_domain' do
+    it 'collapses subdomains to the registrable domain' do
+      expect(described_class.url_to_registrable_domain('https://blog.example.com/posts')).to eq('example.com')
+    end
+
+    it 'keeps multi-part TLDs intact for registrable domain' do
+      expect(described_class.url_to_registrable_domain('https://news.bbc.co.uk/world')).to eq('bbc.co.uk')
+    end
+
+    it 'preserves single-host domains' do
+      expect(described_class.url_to_registrable_domain('https://example.com')).to eq('example.com')
+    end
+
+    it 'returns nil for blank or invalid URLs', :aggregate_failures do
+      expect(described_class.url_to_registrable_domain(nil)).to be_nil
+      expect(described_class.url_to_registrable_domain('')).to be_nil
+      expect(described_class.url_to_registrable_domain('not a url')).to be_nil
+    end
+  end
+
+  describe '.url_to_host_name' do
+    it 'returns the full host' do
+      expect(described_class.url_to_host_name('https://news.bbc.co.uk/world')).to eq('news.bbc.co.uk')
+    end
+
+    it 'returns nil for blank or invalid URLs', :aggregate_failures do
+      expect(described_class.url_to_host_name(nil)).to be_nil
+      expect(described_class.url_to_host_name('')).to be_nil
+      expect(described_class.url_to_host_name('not a url')).to be_nil
+    end
+  end
+
+  describe 'legacy naming guardrail' do
+    it 'does not expose url_to_directory_name' do
+      expect(described_class).not_to respond_to(:url_to_directory_name)
+    end
+  end
+
+  describe '.registrable_domain' do
+    it 'falls back to host when PublicSuffix returns nil' do
+      allow(PublicSuffix).to receive(:domain).with('example.local').and_return(nil)
+
+      expect(described_class.send(:registrable_domain, 'example.local')).to eq('example.local')
+    end
+
+    it 'falls back to host when PublicSuffix raises DomainInvalid' do
+      allow(PublicSuffix).to receive(:domain).with('invalid..host')
+                                             .and_raise(PublicSuffix::DomainInvalid)
+
+      expect(described_class.send(:registrable_domain, 'invalid..host')).to eq('invalid..host')
+    end
+  end
+end
diff --git a/spec/support/helper.rb b/spec/support/helper.rb
index 76ccc32..e97e88a 100644
--- a/spec/support/helper.rb
+++ b/spec/support/helper.rb
@@ -3,16 +3,37 @@
 require 'json'
 require 'nokogiri'
 require 'yaml'
-require 'uri'
+require 'public_suffix'
 
 ##
 # A collection of helper methods.
 module Helper
   ##
   # @param url [String]
+  # @return [String, nil]
+  def self.url_to_registrable_domain(url)
+    host = url_to_host_name(url)
+    return host unless host
+
+    registrable_domain(host)
+  end
+
+  ##
+  # @param url [String]
+  # @return [String, nil]
+  def self.url_to_host_name(url)
+    Html2rss::Url.for_channel(url)&.host
+  rescue ArgumentError
+    nil
+  end
+
+  ##
+  # @param host [String]
   # @return [String]
-  def self.url_to_directory_name(url)
-    URI(url.split('/')[0..2].join('/')).host.gsub(/^(api|www|webapp)\./, '')
+  def self.registrable_domain(host)
+    PublicSuffix.domain(host) || host
+  rescue PublicSuffix::DomainInvalid
+    host
   end
 
   ##
diff --git a/spec/support/shared_examples/config.yml_spec.rb b/spec/support/shared_examples/config.yml_spec.rb
index fa57427..0b7a788 100644
--- a/spec/support/shared_examples/config.yml_spec.rb
+++ b/spec/support/shared_examples/config.yml_spec.rb
@@ -41,16 +41,17 @@
     config
   end
 
-  context 'with the file' do
-    let(:host_name) { Helper.url_to_directory_name yaml['channel']['url'] }
+  context 'with the file' do # rubocop:disable RSpec/MultipleMemoizedHelpers
+    let(:host_name) { Helper.url_to_host_name yaml['channel']['url'] }
+    let(:domain_name) { Helper.url_to_registrable_domain yaml['channel']['url'] }
     let(:dirname) { File.dirname(file_path).split(File::Separator).last }
 
     it 'is parseable' do
       expect { yaml }.not_to raise_error
     end
 
-    it "resides in a folder named after channel.url's host" do
-      expect(dirname).to eq(host_name)
+    it "resides in a folder named after channel.url's host or domain" do
+      expect([domain_name, host_name]).to include(dirname)
     end
   end