diff --git a/_plugins/llms.rb b/_plugins/llms.rb
new file mode 100644
index 0000000000..fec7c0ab0d
--- /dev/null
+++ b/_plugins/llms.rb
@@ -0,0 +1,98 @@
+# frozen_string_literal: true
+
+# Generates /llms.txt and /llms-full.txt (llmstxt.org) from the site
+# itself, so neither can drift from the published pages. llms.txt lists
+# every English page grouped by top-level section, with the title from
+# the front matter and the first sentence of the page as description.
+# llms-full.txt inlines the full Markdown of the same pages for tools
+# that want the whole site in one fetch. News posts appear only as the
+# ten latest links, because two decades of announcements would add over
+# 1 MB of archival text. Rendering is shared with the .md alternates so
+# the outputs stay identical to what those routes serve.
+module LlmsTxt
+  SITE_NAME = "Ruby Programming Language"
+  TAGLINE = "Ruby is a dynamic, open source programming language " \
+            "with a focus on simplicity and productivity. It has an " \
+            "elegant syntax that is natural to read and easy to write."
+
+  # Pages without a title (layout: null fragments such as the homepage
+  # code examples) are not standalone documents and are left out.
+  def self.pages(site)
+    site.pages.select do |page|
+      page.url.start_with?("/en/") && page.data["markdown_url"] && page.data["title"]
+    end.sort_by(&:url)
+  end
+
+  def self.posts(site)
+    site.posts.docs.select {|post| post.data["lang"] == "en" }.last(10).reverse
+  end
+
+  def self.header(site)
+    stable = site.data["downloads"]["stable"].first
+    "# #{SITE_NAME}\n\n> #{TAGLINE} The current stable version is Ruby #{stable}.\n"
+  end
+
+  # First sentence of the first prose paragraph, with images, links,
+  # HTML tags, emphasis and kramdown attribute lines stripped.
+  def self.description(markdown)
+    markdown.split(/\n\s*\n/).each do |block|
+      block = block.strip
+      next if block.empty? || block.start_with?("<", "#", ">", "{%", "|", "*", "-", "!")
+
+      text = block.lines.map(&:strip).reject {|line| line.start_with?("{:") }.join(" ")
+      text = text.gsub(/!\[[^\]]*\](\([^)]*\)|\[[^\]]*\])?/, "")
+                 .gsub(/\[([^\]]*)\](\([^)]*\)|\[[^\]]*\])/, '\1')
+                 .gsub(/<[^>]+>/, " ")
+                 .gsub(/[*_`]/, "")
+                 .squeeze(" ").strip
+      next if text.empty?
+
+      return text[/\A.{10,}?[.!?](?=\s|\z)/m] || text[0, 200]
+    end
+    nil
+  end
+
+  def self.index(site, rendered)
+    out = +header(site)
+
+    pages(site).group_by {|page| page.url.split("/")[2] }.each do |slug, section|
+      front = section.find {|page| page.url == "/en/#{slug}/" }
+      out << "\n## #{front ? front.data["title"] : slug.capitalize}\n\n"
+      section.each do |page|
+        desc = description(rendered[page])
+        out << "- [#{page.data["title"]}](#{site.config["url"]}#{page.data["markdown_url"]})"
+        out << ": #{desc}" if desc
+        out << "\n"
+      end
+    end
+
+    out << "\n## Recent News\n\n"
+    posts(site).each do |post|
+      url = site.config["url"] + post.data["markdown_url"]
+      out << "- [#{post.data["title"]}](#{url}): #{post.date.strftime("%Y-%m-%d")}\n"
+    end
+
+    out << "\n## Optional\n\n"
+    out << "- [llms-full.txt](#{site.config["url"]}/llms-full.txt): " \
+           "All English pages of this site concatenated into a single Markdown file\n"
+  end
+
+  def self.full(site, rendered)
+    sections = pages(site).map do |page|
+      "# #{page.data["title"]}\n\n" \
+      "Source: #{site.config["url"]}#{page.data["markdown_url"]}\n\n" \
+      "#{rendered[page]}\n"
+    end
+
+    ([header(site)] + sections).join("\n---\n\n")
+  end
+end
+
+Jekyll::Hooks.register :site, :post_write do |site|
+  rendered = LlmsTxt.pages(site).to_h do |page|
+    [page, MarkdownAlternates.markdown_for(site, page).strip]
+  end
+
+  File.write(site.in_dest_dir("llms.txt"), LlmsTxt.index(site, rendered))
+  File.write(site.in_dest_dir("llms-full.txt"), LlmsTxt.full(site, rendered))
+end
diff --git a/lib/linter.rb b/lib/linter.rb
index 4296e39c41..925b75ab9a 100644
--- a/lib/linter.rb
+++ b/lib/linter.rb
@@ -18,6 +18,7 @@ class Linter
     %r{\Aadmin/index\.md},
     %r{\A[^/]*/examples/},
     %r{\A_includes/},
+    %r{\A_site/},
     %r{\Atest/},
     %r{\Anode_modules/}
   ].freeze