Using jekyll-archives to create category/tag pages.

Gemfile

@@ -7,6 +7,7 @@ group :jekyll_plugins do
   gem "jekyll-paginate"
   gem "jekyll-redirect-from"
   gem "jekyll-seo-tag", "~> 2.6.1"
+  gem "jekyll-archives"
 end
 
 group :test do

_config.yml

@@ -161,7 +161,6 @@ defaults:
           label: Home
           url: /
 
-
 sass:
   sass_dir: /assets/css
   style: compressed
@@ -198,3 +197,13 @@ sitemap_exclude:  # Sitemap will exclude the following items.
     - sitemap.xml
     - robots.txt
     - redirects.json
+
+# see: <https://github.com/jekyll/jekyll-archives/blob/master/docs/configuration.md>
+jekyll-archives:  
+  enabled: [categories, tags]
+  layouts:
+    category: category
+    tag: tag
+  permalinks:
+    tag: '/tags/:name/'
+    category: '/categories/:name/'

_layouts/category.html

@@ -10,11 +10,11 @@ layout: page
   <h1 class="pl-lg-2">
     <i class="far fa-folder-open fa-fw text-muted"></i>
     {{ page.title }}
-    <span class="lead text-muted pl-2">{{ site.categories[page.category] | size }}</span>
+    <span class="lead text-muted pl-2">{{ page.posts | size }}</span>
   </h1>
 
   <ul class="post-content pl-0">
-    {% for post in site.categories[page.category] %}
+    {% for post in page.posts %}
     <li class="d-flex justify-content-between pl-md-3 pr-md-3">
       <a href="{{ post.url | relative_url }}">{{ post.title }}</a>
       <span class="dash flex-grow-1"></span>

_layouts/tag.html

@@ -11,10 +11,10 @@ layout: page
   <h1 class="pl-lg-2">
     <i class="fa fa-tag fa-fw text-muted"></i>
     {{ page.title }}
-    <span class="lead text-muted pl-2">{{ site.tags[page.tag] | size }}</span>
+    <span class="lead text-muted pl-2">{{ page.posts | size }}</span>
   </h1>
   <ul class="post-content pl-0">
-    {% for post in site.tags[page.tag] %}
+    {% for post in page.posts %}
     <li class="d-flex justify-content-between pl-md-3 pr-md-3">
       <a href="{{ post.url | relative_url }}">{{ post.title }}</a>
       <span class="dash flex-grow-1"></span>