diff --git a/lib/berrypod/application.ex b/lib/berrypod/application.ex
index 2fa3a05..72cace1 100644
--- a/lib/berrypod/application.ex
+++ b/lib/berrypod/application.ex
@@ -44,7 +44,9 @@ defmodule Berrypod.Application do
       # Theme CSS cache - must start after Endpoint for static_path/1 to work
       Berrypod.Theme.CSSCache,
       # Page definition cache - loads page block lists into ETS
-      Berrypod.Pages.PageCache
+      Berrypod.Pages.PageCache,
+      # URL routes cache - custom slugs and prefixes
+      BerrypodWeb.R
     ]
 
     # See https://hexdocs.pm/elixir/Supervisor.html
diff --git a/lib/berrypod_web/r.ex b/lib/berrypod_web/r.ex
new file mode 100644
index 0000000..551c32f
--- /dev/null
+++ b/lib/berrypod_web/r.ex
@@ -0,0 +1,322 @@
+defmodule BerrypodWeb.R do
+  @moduledoc """
+  Runtime URL paths with ETS caching. Short name for ergonomic use.
+
+  This module provides functions for generating URLs that respect custom URL slugs
+  and route prefixes configured by the shop owner.
+
+  ## Usage
+
+      R.cart()              # => "/basket" (if cart is renamed to basket)
+      R.product(123)        # => "/p/123" (if products prefix is "p")
+      R.url(R.product(123)) # => "https://shop.com/p/123"
+
+  ## Page slugs vs route prefixes
+
+  - **Page slugs** are single-segment paths like `/cart`, `/about`, `/contact`
+  - **Route prefixes** are multi-segment paths like `/products/:id`, `/collections/:slug`
+
+  Page slugs are stored on individual Page records. Route prefixes are stored in Settings.
+
+  ## Routing
+
+  The router uses three catch-all routes (`/`, `/:prefix/:id_or_slug`, `/:slug`) that
+  delegate to `Shop.Page`, which resolves the actual page type at runtime using
+  `page_type_from_slug/1` and `prefix_type_from_segment/1`. See the router's
+  "Dynamic Shop Routes" comment block for the full list of handled pages.
+
+  To add a new system page type:
+  1. Add a clause to `default_page_type/1` and `default_slug/1`
+  2. Add the page module to `@page_modules` in `Shop.Page`
+  """
+
+  use GenServer
+
+  alias Berrypod.{Pages, Settings}
+
+  @table __MODULE__
+
+  # =============================================================================
+  # Client API - Path functions
+  # =============================================================================
+
+  @doc "Returns the home page path (always /)."
+  def home, do: "/"
+
+  @doc "Returns the cart page path."
+  def cart, do: "/" <> page_slug(:cart)
+
+  @doc "Returns the about page path."
+  def about, do: "/" <> page_slug(:about)
+
+  @doc "Returns the contact page path."
+  def contact, do: "/" <> page_slug(:contact)
+
+  @doc "Returns the search page path."
+  def search, do: "/" <> page_slug(:search)
+
+  @doc "Returns the delivery page path."
+  def delivery, do: "/" <> page_slug(:delivery)
+
+  @doc "Returns the privacy page path."
+  def privacy, do: "/" <> page_slug(:privacy)
+
+  @doc "Returns the terms page path."
+  def terms, do: "/" <> page_slug(:terms)
+
+  @doc "Returns the checkout success page path."
+  def checkout_success, do: "/" <> page_slug(:checkout_success)
+
+  @doc "Returns the orders page path."
+  def orders, do: "/" <> page_slug(:orders)
+
+  @doc """
+  Returns the path for any page by slug.
+
+  This is a generic version that works with any page slug, including custom pages.
+  Prefer the specific functions (cart/0, about/0, etc.) when the page is known.
+  """
+  def page("home"), do: "/"
+  def page("cart"), do: cart()
+  def page("about"), do: about()
+  def page("contact"), do: contact()
+  def page("search"), do: search()
+  def page("delivery"), do: delivery()
+  def page("privacy"), do: privacy()
+  def page("terms"), do: terms()
+  def page("checkout_success"), do: checkout_success()
+  def page("orders"), do: orders()
+  def page(slug) when is_binary(slug), do: "/" <> slug
+
+  @doc "Returns the path for a specific product."
+  def product(id), do: "/" <> prefix(:products) <> "/" <> to_string(id)
+
+  @doc "Returns the path for a specific collection."
+  def collection(slug), do: "/" <> prefix(:collections) <> "/" <> slug
+
+  @doc "Returns the path for a specific order."
+  def order(order_number), do: "/" <> prefix(:orders) <> "/" <> order_number
+
+  @doc "Returns a full URL (with scheme and host) for the given path."
+  def url(path), do: BerrypodWeb.Endpoint.url() <> path
+
+  # =============================================================================
+  # Reverse lookups (for router)
+  # =============================================================================
+
+  @doc """
+  Given a URL slug, returns the page type it maps to.
+
+  Returns:
+  - `{:page, :cart}` for system pages
+  - `{:custom, page}` for custom pages
+  - `nil` if not found
+  """
+  def page_type_from_slug(slug) do
+    # First check if it's a custom URL slug for a system page
+    case lookup({:reverse_slug, slug}) do
+      {:ok, page_type} ->
+        {:page, page_type}
+
+      :not_found ->
+        # Check if it's a default slug for a system page
+        case default_page_type(slug) do
+          nil ->
+            # Check if it's a custom page
+            case Pages.get_published_page_by_effective_url(slug) do
+              nil -> nil
+              page -> {:custom, page}
+            end
+
+          page_type ->
+            {:page, page_type}
+        end
+    end
+  end
+
+  @doc """
+  Given a URL segment, returns the prefix type it maps to.
+
+  Returns `:products`, `:collections`, `:orders`, or `nil`.
+  """
+  def prefix_type_from_segment(segment) do
+    case lookup({:reverse_prefix, segment}) do
+      {:ok, type} -> type
+      :not_found -> default_prefix_type(segment)
+    end
+  end
+
+  @doc """
+  Returns the current prefix for a given type.
+
+  Used by the DynamicRoutes plug to check if a custom prefix is set.
+
+  ## Examples
+
+      R.prefix(:products)     # => "p" (if customised) or "products" (default)
+      R.prefix(:collections)  # => "c" (if customised) or "collections" (default)
+  """
+  def prefix(prefix_type) do
+    key = {:prefix, prefix_type}
+
+    case lookup(key) do
+      {:ok, prefix} -> prefix
+      :not_found -> default_prefix(prefix_type)
+    end
+  end
+
+  # =============================================================================
+  # Cache management
+  # =============================================================================
+
+  @doc "Invalidates a specific cache key."
+  def invalidate(key) do
+    GenServer.cast(__MODULE__, {:invalidate, key})
+  end
+
+  @doc "Invalidates all cache entries (use after prefix changes)."
+  def invalidate_all do
+    GenServer.cast(__MODULE__, :invalidate_all)
+  end
+
+  @doc "Invalidates all cache entries synchronously. Use when you need the cache refreshed before proceeding."
+  def invalidate_all_sync do
+    GenServer.call(__MODULE__, :invalidate_all)
+  end
+
+  @doc "Clears all cache entries without re-warming. Used in tests to reset to defaults."
+  def clear do
+    GenServer.call(__MODULE__, :clear)
+  end
+
+  @doc "Warms the cache with current values from the database."
+  def warm_cache do
+    GenServer.cast(__MODULE__, :warm_cache)
+  end
+
+  # =============================================================================
+  # GenServer
+  # =============================================================================
+
+  def start_link(_opts) do
+    GenServer.start_link(__MODULE__, [], name: __MODULE__)
+  end
+
+  @impl GenServer
+  def init(_) do
+    :ets.new(@table, [:named_table, :public, read_concurrency: true])
+    do_warm_cache()
+    {:ok, %{}}
+  end
+
+  @impl GenServer
+  def handle_cast({:invalidate, key}, state) do
+    :ets.delete(@table, key)
+    {:noreply, state}
+  end
+
+  def handle_cast(:invalidate_all, state) do
+    :ets.delete_all_objects(@table)
+    do_warm_cache()
+    {:noreply, state}
+  end
+
+  def handle_cast(:warm_cache, state) do
+    do_warm_cache()
+    {:noreply, state}
+  end
+
+  @impl GenServer
+  def handle_call(:invalidate_all, _from, state) do
+    :ets.delete_all_objects(@table)
+    do_warm_cache()
+    {:reply, :ok, state}
+  end
+
+  def handle_call(:clear, _from, state) do
+    :ets.delete_all_objects(@table)
+    {:reply, :ok, state}
+  end
+
+  # =============================================================================
+  # Private - Cache operations
+  # =============================================================================
+
+  defp page_slug(page_type) do
+    key = {:slug, page_type}
+
+    case lookup(key) do
+      {:ok, slug} -> slug
+      :not_found -> default_slug(page_type)
+    end
+  end
+
+  defp lookup(key) do
+    case :ets.lookup(@table, key) do
+      [{^key, value}] -> {:ok, value}
+      [] -> :not_found
+    end
+  rescue
+    ArgumentError -> :not_found
+  end
+
+  defp do_warm_cache do
+    # Load page slugs
+    Pages.list_pages_with_custom_urls()
+    |> Enum.each(fn page ->
+      page_type = String.to_existing_atom(page.slug)
+      :ets.insert(@table, {{:slug, page_type}, page.url_slug})
+      :ets.insert(@table, {{:reverse_slug, page.url_slug}, page_type})
+    end)
+
+    # Load route prefixes from settings
+    prefixes = Settings.get_setting("url_prefixes") || %{}
+
+    Enum.each(prefixes, fn {type_str, prefix} ->
+      type = String.to_existing_atom(type_str)
+      :ets.insert(@table, {{:prefix, type}, prefix})
+      :ets.insert(@table, {{:reverse_prefix, prefix}, type})
+    end)
+  rescue
+    # During startup, tables/atoms might not exist yet
+    _ -> :ok
+  end
+
+  # =============================================================================
+  # Defaults
+  # =============================================================================
+
+  defp default_slug(:cart), do: "cart"
+  defp default_slug(:about), do: "about"
+  defp default_slug(:contact), do: "contact"
+  defp default_slug(:search), do: "search"
+  defp default_slug(:delivery), do: "delivery"
+  defp default_slug(:privacy), do: "privacy"
+  defp default_slug(:terms), do: "terms"
+  defp default_slug(:checkout_success), do: "checkout/success"
+  defp default_slug(:orders), do: "orders"
+  defp default_slug(_), do: nil
+
+  defp default_prefix(:products), do: "products"
+  defp default_prefix(:collections), do: "collections"
+  defp default_prefix(:orders), do: "orders"
+  defp default_prefix(_), do: nil
+
+  # Map default slugs back to page types (for router)
+  defp default_page_type("cart"), do: :cart
+  defp default_page_type("about"), do: :about
+  defp default_page_type("contact"), do: :contact
+  defp default_page_type("search"), do: :search
+  defp default_page_type("delivery"), do: :delivery
+  defp default_page_type("privacy"), do: :privacy
+  defp default_page_type("terms"), do: :terms
+  defp default_page_type("orders"), do: :orders
+  defp default_page_type("checkout/success"), do: :checkout_success
+  defp default_page_type(_), do: nil
+
+  # Map default prefixes back to types
+  defp default_prefix_type("products"), do: :products
+  defp default_prefix_type("collections"), do: :collections
+  defp default_prefix_type("orders"), do: :orders
+  defp default_prefix_type(_), do: nil
+end
diff --git a/test/berrypod_web/r_test.exs b/test/berrypod_web/r_test.exs
new file mode 100644
index 0000000..20a88a0
--- /dev/null
+++ b/test/berrypod_web/r_test.exs
@@ -0,0 +1,89 @@
+defmodule BerrypodWeb.RTest do
+  use Berrypod.DataCase, async: false
+
+  alias BerrypodWeb.R
+  alias Berrypod.Pages
+
+  setup do
+    # Clear caches between tests
+    R.invalidate_all_sync()
+    Berrypod.Pages.PageCache.invalidate_all()
+    :ok
+  end
+
+  describe "page path functions" do
+    test "returns default paths when no custom slugs set" do
+      assert R.cart() == "/cart"
+      assert R.about() == "/about"
+      assert R.contact() == "/contact"
+      assert R.search() == "/search"
+    end
+
+    test "returns custom path after url_slug is set" do
+      {:ok, _} = Pages.update_page_url_slug("cart", "basket")
+
+      assert R.cart() == "/basket"
+    end
+
+    test "returns default path after url_slug is cleared" do
+      {:ok, _} = Pages.update_page_url_slug("about", "our-story")
+      assert R.about() == "/our-story"
+
+      {:ok, _} = Pages.update_page_url_slug("about", "")
+      assert R.about() == "/about"
+    end
+  end
+
+  describe "page/1 generic function" do
+    test "routes through specific functions for system pages" do
+      {:ok, _} = Pages.update_page_url_slug("cart", "basket")
+
+      assert R.page("cart") == "/basket"
+      assert R.page("home") == "/"
+    end
+
+    test "returns /slug for custom pages" do
+      assert R.page("my-custom-page") == "/my-custom-page"
+    end
+  end
+
+  describe "reverse lookups" do
+    test "page_type_from_slug finds system page by custom url" do
+      {:ok, _} = Pages.update_page_url_slug("about", "our-story")
+
+      assert R.page_type_from_slug("our-story") == {:page, :about}
+    end
+
+    test "page_type_from_slug finds system page by default url" do
+      assert R.page_type_from_slug("cart") == {:page, :cart}
+      assert R.page_type_from_slug("about") == {:page, :about}
+    end
+
+    test "page_type_from_slug returns nil for unknown slug" do
+      assert R.page_type_from_slug("nonexistent") == nil
+    end
+
+    test "page_type_from_slug finds custom page" do
+      {:ok, _} = Pages.create_custom_page(%{slug: "faq", title: "FAQ", published: true})
+
+      assert {:custom, page} = R.page_type_from_slug("faq")
+      assert page.slug == "faq"
+    end
+  end
+
+  describe "prefix functions" do
+    test "returns default prefixes" do
+      assert R.product(123) == "/products/123"
+      assert R.collection("art") == "/collections/art"
+      assert R.order("ORD-123") == "/orders/ORD-123"
+    end
+  end
+
+  describe "url/1" do
+    test "prepends endpoint URL to path" do
+      url = R.url("/cart")
+      assert String.starts_with?(url, "http")
+      assert String.ends_with?(url, "/cart")
+    end
+  end
+end