diff --git a/.yardopts b/.yardopts
new file mode 100644
index 0000000..505c853
--- /dev/null
+++ b/.yardopts
@@ -0,0 +1,4 @@
+--markup markdown
+--readme README.md
+--protected
+--private
diff --git a/Rakefile b/Rakefile
index 1061dcb..5ae7307 100644
--- a/Rakefile
+++ b/Rakefile
@@ -2,11 +2,14 @@
 
 require 'bundler/gem_tasks'
 
+CLEAN << '.yardoc'
+CLEAN << 'doc'
+
 desc 'Run default checks'
 task default: %i[lint]
 
 desc 'Run code analysis tools'
-task lint: %i[rubocop]
+task lint: %i[rubocop yard:cov]
 
 desc 'Fix code style (rubocop --auto-correct)'
 task fix: 'rubocop:auto_correct'
@@ -18,7 +21,27 @@ rescue LoadError
   nil
 end
 
+begin
+  require 'yard'
+  YARD::Rake::YardocTask.new
+rescue LoadError
+  nil
+end
+
 desc 'Open development console'
 task :console do
   exec 'bundle', 'exec', File.expand_path(File.join('bin', 'console'), __dir__)
 end
+
+namespace :yard do
+  desc 'Measure documentation coverage'
+  task :cov do
+    result = `bundle exec yard stats`.lines.last.strip.freeze
+    m = result.match(/\A(\d+(\.\d+)?)% documented\z/)
+    raise 'Invalid result' if m.nil?
+
+    coverage = m[1].to_f.round(2)
+    puts "Documentation coverage: #{coverage}%"
+    # TODO: raise 'Not fully documented!' if coverage != 100
+  end
+end
diff --git a/diversipub.gemspec b/diversipub.gemspec
index e1c0e38..4725d41 100644
--- a/diversipub.gemspec
+++ b/diversipub.gemspec
@@ -52,4 +52,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'rake',                '~> 13.0'
   spec.add_development_dependency 'rubocop-performance', '~> 1.13'
   spec.add_development_dependency 'rubocop-rake',        '~> 0.6'
+  spec.add_development_dependency 'yard',                '~> 0.9'
 end
diff --git a/lib/diversipub.rb b/lib/diversipub.rb
index f25f413..d60b032 100644
--- a/lib/diversipub.rb
+++ b/lib/diversipub.rb
@@ -25,3 +25,9 @@ require_relative 'diversipub/puma_task'
 require_relative 'diversipub/rack_app'
 require_relative 'diversipub/sinatra_app'
 require_relative 'diversipub/version'
+
+##
+# A publishing platform for HTTP, Gemini, ActivityPub, RSS, Atom, and others.
+#
+module Diversipub
+end
diff --git a/lib/diversipub/version.rb b/lib/diversipub/version.rb
index 82c96ae..b50501f 100644
--- a/lib/diversipub/version.rb
+++ b/lib/diversipub/version.rb
@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 
 module Diversipub
+  # Gem version.
   VERSION = '0.0.0'
 end