Use jekyll-last-modified-at

Gemfile

@@ -5,6 +5,7 @@ gem 'jekyll-paginate', group: :jekyll_plugins
 gem 'jekyll-compose', group: :jekyll_plugins
 gem 'jekyll-minifier', group: :jekyll_plugins
 gem 'jekyll-sitemap', group: :jekyll_plugins
+gem 'jekyll-last-modified-at', group: :jekyll_plugins
 gem 'jekyll-tagging', group: :jekyll_plugins
 gem 'nokogiri'
 gem 'fastimage'

Gemfile.lock

@@ -33,6 +33,9 @@ GEM
       safe_yaml (~> 1.0)
     jekyll-compose (0.7.0)
       jekyll (~> 3.0)
+    jekyll-last-modified-at (1.0.1)
+      jekyll (~> 3.3)
+      posix-spawn (~> 0.3.9)
     jekyll-minifier (0.1.5)
       cssminify2 (~> 2.0)
       htmlcompressor (~> 0.3)
@@ -60,6 +63,7 @@ GEM
     nuggets (1.5.0)
     pathutil (0.16.1)
       forwardable-extended (~> 2.6)
+    posix-spawn (0.3.13)
     public_suffix (3.0.2)
     rb-fsevent (0.10.3)
     rb-inotify (0.9.10)
@@ -82,6 +86,7 @@ DEPENDENCIES
   fastimage
   jekyll
   jekyll-compose
+  jekyll-last-modified-at
   jekyll-minifier
   jekyll-paginate
   jekyll-sitemap

_config.yml

@@ -44,10 +44,17 @@ kramdown:
 
 plugins:
 - jekyll-paginate
+- jekyll-last-modified-at
 
 permalink: /:categories/:year-:month-:day-:title.html
 strict_front_matter: true
 
+defaults:
+- scope:
+    path: "tag/"
+  values:
+    sitemap: false
+
 # jekyll-tagging
 tag_page_layout: tag_page
 tag_page_dir: tag

_includes/metadata.json

@@ -5,7 +5,7 @@
   "mainEntityOfPage": "{{ page.url | replace:'index.html','' | prepend: site.baseurl | prepend: site.url }}",
   "headline": "{% if page.title %}{{ page.title | escape }}{% else %}{{ site.title | escape }}{% endif %}",
   "datePublished": "{% if page.date %}{{ page.date | date_to_xmlschema }}{% else %}{{ site.time | date_to_xmlschema }}{% endif %}",
-  "dateModified": "{% if page.date %}{{ page.date | date_to_xmlschema }}{% else %}{{ site.time | date_to_xmlschema }}{% endif %}",
+  "dateModified": "{% if page.last_modified_at %}{{ page.last_modified_at | date_to_xmlschema }}{% elsif page.date %}{{ page.date | date_to_xmlschema }}{% else %}{{ site.time | date_to_xmlschema }}{% endif %}",
   "description": "{% if page.excerpt %}{{ page.excerpt | strip_html | strip_newlines | truncate: 160 }}{% else %}{{ site.description }}{% endif %}",
   "author": {
     "@type": "Person",

_layouts/post.html

@@ -7,6 +7,7 @@
       <h1 class="post-title">{{ page.title }}</h1>
       <div>Tags: {{ page | tags }}</div>
       <div>Created at: {{ page.date | date: "%Y-%m-%d %H:%M:%S" }}</div>
+      <div>Last modified at: {{ page.last_modified_at | date: "%Y-%m-%d %H:%M:%S" }}</div>
     </div>
 
     <section class="post-content">

_plugins/skip_last_modified_at.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+require 'jekyll-last-modified-at/determinator'
+
+module SkipLastModifiedAt
+  def last_modified_at_time
+    return if page_path == 'index.html' # jekyll-paginate
+    return if %r!\Atag/! =~ page_path # jekyll-tagging
+    super
+  end
+end
+class Jekyll::LastModifiedAt::Determinator
+  prepend SkipLastModifiedAt
+end