Add a rake docs:preview task serving the docs site locally

.gitignore

@@ -9,3 +9,7 @@
 /spec/reports/
 /tmp/
 Gemfile.lock
+docs/_site/
+docs/.jekyll-cache/
+docs/.jekyll-metadata
+docs/_data/versions.yml

AGENTS.md

@@ -17,6 +17,7 @@ This is the official Ruby SDK for the Model Context Protocol (MCP), implementing
 - `rake rubocop` - Run linter
 - `rake` - Run tests and linting (default task)
 - `bundle exec rake conformance` - Run the MCP conformance suite (see conformance/README.md)
+- `bundle exec rake docs:preview` - Serve the documentation site locally at http://localhost:4000 (PORT to override)
 - `ruby -I lib -I test test/path/to/specific_test.rb` - Run single test file
 - `gem build mcp.gemspec` - Build the gem
 

Rakefile

@@ -51,6 +51,42 @@ task :conformance_server do
   Conformance::Server.new(**options).start
 end
 
+namespace :docs do
+  desc "Serve the documentation site locally at http://localhost:4000 (PORT)"
+  task :preview do
+    docs_dir = File.expand_path("docs", __dir__)
+    generate_docs_versions_data(docs_dir)
+
+    env = {
+      "BUNDLE_GEMFILE" => File.join(docs_dir, "Gemfile"),
+      "RUBYOPT" => "-r#{File.join(docs_dir, "_preview", "taint_shim.rb")}",
+    }
+    port = ENV.fetch("PORT", "4000")
+
+    Bundler.with_unbundled_env do
+      system(env, "bundle", "install", "--quiet", chdir: docs_dir, exception: true)
+      system(env, "bundle", "exec", "jekyll", "serve", "--port", port, chdir: docs_dir, exception: true)
+    rescue Interrupt
+      # Ctrl-C is the way to stop the preview, not an error.
+    end
+  end
+end
+
+# Mirrors bin/generate-gh-pages.sh: the released site receives `_data/versions.yml` from
+# the version tags at deploy time, and the preview generates the same data so the nav footer
+# shows the released-gem version line.
+def generate_docs_versions_data(docs_dir)
+  versions = %x(git tag --list).split("\n").filter_map { |tag|
+    tag[/\A[^0-9]*(\d+\.\d+\.\d+(?:-[a-zA-Z0-9.-]+)?)\z/, 1]
+  }.sort_by { |version|
+    Gem::Version.new(version)
+  }.reverse
+  return if versions.empty?
+
+  mkdir_p(File.join(docs_dir, "_data"))
+  File.write(File.join(docs_dir, "_data", "versions.yml"), versions.map { |version| "- #{version}\n" }.join)
+end
+
 def npx_available?(task_name)
   return true if system("which", "npx", out: File::NULL, err: File::NULL)
 

docs/Gemfile

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+# Dependencies for the local docs preview (`rake docs:preview`), kept out of the gem's own Gemfile:
+# github-pages mirrors the GitHub Pages runtime that builds the released site
+# (jekyll-remote-theme, jekyll-redirect-from, and the Jekyll version Pages actually runs).
+source "https://rubygems.org"
+
+gem "github-pages", group: :jekyll_plugins
+gem "webrick"
+
+# Former default gems that the Jekyll version pinned by github-pages still requires on Ruby 4.0.
+gem "base64"
+gem "bigdecimal"
+gem "csv"
+gem "logger"

docs/_preview/taint_shim.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+# Liquid 4.0.3 (pinned by github-pages) still calls the taint API that Ruby 3.2 removed.
+# Restore it as a no-op for the local docs preview only; `rake docs:preview` loads
+# this file via `RUBYOPT`, so nothing outside the preview process is affected.
+class Object
+  def tainted?
+    false
+  end
+
+  def taint
+    self
+  end
+
+  def untaint
+    self
+  end
+end