diff --git a/lib/bds/generation/data.ex b/lib/bds/generation/data.ex
index 9bcf2f6..962053f 100644
--- a/lib/bds/generation/data.ex
+++ b/lib/bds/generation/data.ex
@@ -175,6 +175,7 @@ defmodule BDS.Generation.Data do
         end)
       end
     )
+    |> sort_generation_index_posts()
   end
 
   ## --- internals -----------------------------------------------------------
@@ -398,4 +399,17 @@ defmodule BDS.Generation.Data do
   defp append_generation_index(index, field, key, post) do
     update_in(index[field], fn grouped -> Map.update(grouped, key, [post], &[post | &1]) end)
   end
+
+  # Archive listings (categories, tags, dates) must render newest first. The
+  # index is built by prepending, so each grouped list is sorted explicitly by
+  # creation date (descending) to guarantee a stable newest-first order.
+  defp sort_generation_index_posts(index) do
+    Map.new(index, fn {field, grouped} ->
+      {field, Map.new(grouped, fn {key, posts} -> {key, sort_index_posts_desc(posts)} end)}
+    end)
+  end
+
+  defp sort_index_posts_desc(posts) do
+    Enum.sort_by(posts, &{-(&1.created_at || 0), -(&1.published_at || 0), to_string(&1.slug)})
+  end
 end
diff --git a/lib/bds/rendering/list_archive.ex b/lib/bds/rendering/list_archive.ex
index 2c52868..8c2edde 100644
--- a/lib/bds/rendering/list_archive.ex
+++ b/lib/bds/rendering/list_archive.ex
@@ -273,7 +273,7 @@ defmodule BDS.Rendering.ListArchive do
           |> DateTime.to_date()
           |> Date.to_iso8601())
       )
-      |> Enum.sort_by(fn {label, _posts} -> label end)
+      |> Enum.sort_by(fn {label, _posts} -> label end, :desc)
 
     last_index = length(grouped_blocks) - 1
 
@@ -284,7 +284,7 @@ defmodule BDS.Rendering.ListArchive do
         date_label: date_label,
         show_date_marker: true,
         show_separator: index < last_index,
-        posts: Enum.sort_by(grouped_posts, &Map.get(&1, :created_at))
+        posts: Enum.sort_by(grouped_posts, &Map.get(&1, :created_at), :desc)
       }
     end)
     |> case do
diff --git a/test/bds/generation/archive_ordering_test.exs b/test/bds/generation/archive_ordering_test.exs
new file mode 100644
index 0000000..28e9c47
--- /dev/null
+++ b/test/bds/generation/archive_ordering_test.exs
@@ -0,0 +1,39 @@
+defmodule BDS.Generation.ArchiveOrderingTest do
+  @moduledoc """
+  Category, tag and date archive listings must render newest first. The
+  generation post index is built by prepending, so this guards against the
+  regression where grouped archive lists came out in an unstable/oldest-first
+  order.
+  """
+  use ExUnit.Case, async: true
+
+  alias BDS.Generation.Data
+
+  defp post(slug, created_at, categories, tags) do
+    %{
+      id: slug,
+      slug: slug,
+      created_at: created_at,
+      published_at: created_at,
+      categories: categories,
+      tags: tags
+    }
+  end
+
+  test "categories, tags and dates are ordered newest first regardless of input order" do
+    older = post("older", 1_700_000_000_000, ["article"], ["elixir"])
+    newest = post("newest", 1_700_000_200_000, ["article"], ["elixir"])
+    middle = post("middle", 1_700_000_100_000, ["article"], ["elixir"])
+
+    # Deliberately unordered input.
+    index = Data.build_generation_post_index([older, newest, middle])
+
+    expected = ["newest", "middle", "older"]
+
+    assert Enum.map(index.posts_by_category["article"], & &1.slug) == expected
+    assert Enum.map(index.posts_by_tag["elixir"], & &1.slug) == expected
+
+    {year, _month, _day} = BDS.Generation.Paths.local_date_parts!(newest.created_at)
+    assert Enum.map(index.posts_by_year[year], & &1.slug) == expected
+  end
+end
diff --git a/test/bds/rendering_test.exs b/test/bds/rendering_test.exs
index 65b846f..f17dbbb 100644
--- a/test/bds/rendering_test.exs
+++ b/test/bds/rendering_test.exs
@@ -246,7 +246,7 @@ defmodule BDS.RenderingTest do
                title: "Render Day Blocks",
                kind: :list,
                content:
-                 "range={{ min_date }}-{{ max_date }}|heading={{ show_archive_range_heading }}|blocks={% for block in day_blocks %}[{{ block.date_label }}:{{ block.posts.size }}:{{ block.show_date_marker }}]{% endfor %}|archive={{ archive_context.kind }}:{{ archive_context.year }}:{{ archive_context.month }}"
+                 "range={{ min_date }}-{{ max_date }}|heading={{ show_archive_range_heading }}|blocks={% for block in day_blocks %}[{{ block.date_label }}:{% for p in block.posts %}{{ p.slug }};{% endfor %}:{{ block.show_date_marker }}]{% endfor %}|archive={{ archive_context.kind }}:{{ archive_context.year }}:{{ archive_context.month }}"
              })
 
     assert {:ok, published_list_template} = BDS.Templates.publish_template(list_template.id)
@@ -289,6 +289,19 @@ defmodule BDS.RenderingTest do
         tags: [],
         categories: [],
         href: "/2024/04/01/second/"
+      },
+      %{
+        id: "second-b",
+        slug: "second-b",
+        title: "Second B",
+        excerpt: "two-b",
+        language: "en",
+        created_at: second_day + 3_600,
+        updated_at: second_day + 3_600,
+        published_at: second_day + 3_600,
+        tags: [],
+        categories: [],
+        href: "/2024/04/01/second-b/"
       }
     ]
 
@@ -311,9 +324,9 @@ defmodule BDS.RenderingTest do
              })
 
     assert rendered =~ "heading=true"
-    assert rendered =~ "blocks=[2024-03-31:1:true][2024-04-01:1:true]"
+    assert rendered =~ "blocks=[2024-04-01:second-b;second;:true][2024-03-31:first;:true]"
     assert rendered =~ "archive=date:2024:4"
-    assert rendered =~ "range=1711843200-1711929600"
+    assert rendered =~ "range=1711843200-1711933200"
   end
 
   test "render_post_page falls back to bundled starter template when the published default template file is missing",
diff --git a/tmp_preview_check.exs b/tmp_preview_check.exs
new file mode 100644
index 0000000..98b112f
--- /dev/null
+++ b/tmp_preview_check.exs
@@ -0,0 +1,38 @@
+Application.ensure_all_started(:ecto_sql)
+Application.ensure_all_started(:exqlite)
+{:ok, _} = BDS.Repo.start_link()
+
+project_id = "aceac6d3-8f3f-4a9c-a2b4-517b59b20f44"
+
+# 1) Replicate the preview data path exactly.
+import Ecto.Query
+alias BDS.Posts.Post
+
+posts =
+  BDS.Repo.all(
+    from p in Post,
+      where: p.project_id == ^project_id and p.status in [:published, :draft],
+      order_by: [desc: p.created_at, desc: p.published_at, asc: p.slug]
+  )
+
+picture = Enum.filter(posts, fn p -> "picture" in (p.categories || []) end)
+
+IO.puts("== preview data path, first 5 (expect newest) ==")
+picture |> Enum.take(5) |> Enum.each(fn p -> IO.puts("  #{p.slug}  #{p.created_at}  #{p.language}") end)
+
+# 2) Call the actual router render and extract the first post links.
+case BDS.Preview.Router.render_route(project_id, "/category/picture") do
+  {:ok, %{body: body}} ->
+    body = IO.iodata_to_binary(body)
+
+    links =
+      Regex.scan(~r{href="[^"]*/20\d\d/\d\d/[^"]*"}, body)
+      |> Enum.map(&hd/1)
+      |> Enum.take(6)
+
+    IO.puts("== render_route /category/picture, first link hrefs ==")
+    Enum.each(links, &IO.puts("  #{&1}"))
+
+  other ->
+    IO.inspect(other, label: "render_route returned")
+end