diff --git a/lib/ash.ex b/lib/ash.ex
index fef2446d..608d9af0 100644
--- a/lib/ash.ex
+++ b/lib/ash.ex
@@ -2,11 +2,9 @@ defmodule Ash do
   @moduledoc """
   The primary interface for interrogating apis and resources.
 
-  This is not the code level interface for a resource. Instead, call functions
-  on an `Api` module that contains those resources. This is for retrieving
-  resource/api configurations.
+  These are tools for interrogating resources to derive behavior based on their
+  configuration. This is how all of the behavior of Ash is ultimately configured.
   """
-  alias Ash.Error
   alias Ash.Resource.Actions.{Create, Destroy, Read, Update}
   alias Ash.Resource.Relationships.{BelongsTo, HasMany, HasOne, ManyToMany}
 
@@ -32,77 +30,31 @@ defmodule Ash do
   @type query :: Ash.Query.t()
   @type actor :: Ash.record()
 
-  defmacro partial_resource(do: body) do
-    quote do
-      defmacro __using__(_) do
-        body = unquote(body)
-
-        quote do
-          unquote(body)
-        end
-      end
-    end
-  end
-
-  def ash_error?(value) do
-    !!Ash.Error.impl_for(value)
-  end
-
-  def to_ash_error(values) when is_list(values) do
-    values =
-      Enum.map(values, fn value ->
-        if ash_error?(value) do
-          value
-        else
-          Error.Unknown.exception(error: values)
-        end
-      end)
-
-    Error.choose_error(values)
-  end
-
-  def to_ash_error(value) do
-    to_ash_error([value])
-  end
-
+  @doc "A short description of the resource, to be included in autogenerated documentation"
+  @spec describe(resource()) :: String.t()
   def describe(resource) do
     resource.describe()
   end
 
+  @doc "A list of authorizers to be used when accessing the resource"
+  @spec authorizers(resource()) :: [module]
   def authorizers(resource) do
     resource.authorizers()
   end
 
-  @spec resource_module?(module) :: boolean
-  def resource_module?(module) do
-    :attributes
-    |> module.module_info()
-    |> Keyword.get(:behaviour, [])
-    |> Enum.any?(&(&1 == Ash.Resource))
-  end
-
-  @spec data_layer_can?(resource(), Ash.DataLayer.feature()) :: boolean
-  def data_layer_can?(resource, feature) do
-    data_layer = data_layer(resource)
-
-    data_layer && data_layer.can?(resource, feature)
-  end
-
-  @spec data_layer_filters(resource) :: map
-  def data_layer_filters(resource) do
-    Ash.DataLayer.custom_filters(resource)
-  end
-
+  @doc "A list of resource modules for a given API"
   @spec resources(api) :: list(resource())
   def resources(api) do
     api.resources()
   end
 
+  @doc "A list of field names corresponding to the primary key of a resource"
   @spec primary_key(resource()) :: list(atom)
   def primary_key(resource) do
     resource.primary_key()
   end
 
+  @doc "Gets a relationship by name from the resource"
   @spec relationship(resource(), atom() | String.t()) :: relationship() | nil
   def relationship(resource, relationship_name) when is_bitstring(relationship_name) do
     Enum.find(resource.relationships(), &(to_string(&1.name) == relationship_name))
@@ -112,11 +64,13 @@ defmodule Ash do
     Enum.find(resource.relationships(), &(&1.name == relationship_name))
   end
 
+  @doc "A list of relationships on the resource"
   @spec relationships(resource()) :: list(relationship())
   def relationships(resource) do
     resource.relationships()
   end
 
+  @doc false
   def primary_action!(resource, type) do
     case primary_action(resource, type) do
       nil -> raise "Required primary #{type} action for #{inspect(resource)}"
@@ -124,6 +78,7 @@ defmodule Ash do
     end
   end
 
+  @doc "Returns the primary action of a given type for a resource"
   @spec primary_action(resource(), atom()) :: action() | nil
   def primary_action(resource, type) do
     resource
@@ -135,16 +90,19 @@ defmodule Ash do
     end
   end
 
+  @doc "Returns the action with the matching name and type on the resource"
   @spec action(resource(), atom(), atom()) :: action() | nil
   def action(resource, name, type) do
     Enum.find(resource.actions(), &(&1.name == name && &1.type == type))
   end
 
+  @doc "A list of all actions on the resource"
   @spec actions(resource()) :: list(action())
   def actions(resource) do
     resource.actions()
   end
 
+  @doc "Get an attribute name from the resource"
   @spec attribute(resource(), String.t() | atom) :: attribute() | nil
   def attribute(resource, name) when is_bitstring(name) do
     Enum.find(resource.attributes, &(to_string(&1.name) == name))
@@ -154,23 +112,41 @@ defmodule Ash do
     Enum.find(resource.attributes, &(&1.name == name))
   end
 
+  @doc "A list of all attributes on the resource"
   @spec attributes(resource()) :: list(attribute())
   def attributes(resource) do
     resource.attributes()
   end
 
+  @doc "The name of the resource, e.g 'posts'"
   @spec name(resource()) :: String.t()
   def name(resource) do
     resource.name()
   end
 
+  @doc "The type of the resource, e.g 'post'"
   @spec type(resource()) :: String.t()
   def type(resource) do
     resource.type()
   end
 
+  @doc "The data layer of the resource, or nil if it does not have one"
   @spec data_layer(resource()) :: data_layer()
   def data_layer(resource) do
     resource.data_layer()
   end
+
+  @doc false
+  @spec data_layer_can?(resource(), Ash.DataLayer.feature()) :: boolean
+  def data_layer_can?(resource, feature) do
+    data_layer = data_layer(resource)
+
+    data_layer && Ash.DataLayer.can?(feature, resource)
+  end
+
+  @doc false
+  @spec data_layer_filters(resource) :: map
+  def data_layer_filters(resource) do
+    Ash.DataLayer.custom_filters(resource)
+  end
 end
diff --git a/lib/ash/actions/relationships.ex b/lib/ash/actions/relationships.ex
index ad4cba66..7c4b3272 100644
--- a/lib/ash/actions/relationships.ex
+++ b/lib/ash/actions/relationships.ex
@@ -227,7 +227,7 @@ defmodule Ash.Actions.Relationships do
       !is_map(data) ->
         validate_map_replace(relationship, data)
 
-      Map.get(data, :__struct__) && Ash.resource_module?(data.__struct__) ->
+      Map.get(data, :__struct__) ->
         validate_struct_replace(relationship, data, action_type)
 
       true ->
diff --git a/lib/ash/data_layer/ets.ex b/lib/ash/data_layer/ets.ex
index 32d96791..1bed4c28 100644
--- a/lib/ash/data_layer/ets.ex
+++ b/lib/ash/data_layer/ets.ex
@@ -9,9 +9,12 @@ defmodule Ash.DataLayer.Ets do
 
   alias Ash.Filter.{And, Eq, In, NotEq, NotIn, Or}
 
+  @callback ets_private?() :: boolean
+
   defmacro __using__(opts) do
     quote bind_quoted: [opts: opts] do
       @data_layer Ash.DataLayer.Ets
+      @behaviour Ash.DataLayer.Ets
 
       @ets_private? Keyword.get(opts, :private?, false)
 
@@ -21,6 +24,7 @@ defmodule Ash.DataLayer.Ets do
     end
   end
 
+  @spec private?(Ash.resource()) :: boolean
   def private?(resource) do
     resource.ets_private?()
   end
@@ -31,7 +35,6 @@ defmodule Ash.DataLayer.Ets do
   end
 
   @impl true
-
   def can?(resource, :async_engine) do
     not private?(resource)
   end
diff --git a/lib/ash/engine/engine.ex b/lib/ash/engine/engine.ex
index 673e6e38..f88debe9 100644
--- a/lib/ash/engine/engine.ex
+++ b/lib/ash/engine/engine.ex
@@ -336,7 +336,7 @@ defmodule Ash.Engine do
   end
 
   defp to_ash_error(error) do
-    if Ash.ash_error?(error) do
+    if Ash.Error.ash_error?(error) do
       error
     else
       Unknown.exception(error: error)
diff --git a/lib/ash/engine/runner.ex b/lib/ash/engine/runner.ex
index ec17e4e4..ba71146a 100644
--- a/lib/ash/engine/runner.ex
+++ b/lib/ash/engine/runner.ex
@@ -422,7 +422,7 @@ defmodule Ash.Engine.Runner do
   end
 
   defp to_ash_error(error) do
-    if Ash.ash_error?(error) do
+    if Ash.Error.ash_error?(error) do
       error
     else
       Unknown.exception(error: error)
diff --git a/lib/ash/error.ex b/lib/ash/error.ex
index fc29d6cf..f190df50 100644
--- a/lib/ash/error.ex
+++ b/lib/ash/error.ex
@@ -21,6 +21,27 @@ defmodule Ash.Error do
 
   @error_class_indices @error_classes |> Enum.with_index() |> Enum.into(%{})
 
+  def ash_error?(value) do
+    !!impl_for(value)
+  end
+
+  def to_ash_error(values) when is_list(values) do
+    values =
+      Enum.map(values, fn value ->
+        if ash_error?(value) do
+          value
+        else
+          Error.Unknown.exception(error: values)
+        end
+      end)
+
+    Error.choose_error(values)
+  end
+
+  def to_ash_error(value) do
+    to_ash_error([value])
+  end
+
   def choose_error(errors) do
     [error | _other_errors] = Enum.sort_by(errors, &Map.get(@error_class_indices, &1.class))
 
diff --git a/lib/ash/resource.ex b/lib/ash/resource.ex
index b4cf9a5a..596a2d97 100644
--- a/lib/ash/resource.ex
+++ b/lib/ash/resource.ex
@@ -18,14 +18,36 @@ defmodule Ash.Resource do
 
   Resource DSL documentation: `Ash.Resource.DSL`
 
+  The following options apply to `use Ash.Resource, [...]`
   #{NimbleOptions.docs(@resource_opts_schema)}
 
+  For more information on the resource DSL, see `Ash.Resource.DSL`
+
   Note:
   *Do not* call the functions on a resource, as in `MyResource.type()` as this is a *private*
   API and can change at any time. Instead, use the `Ash` module, for example: `Ash.type(MyResource)`
   """
 
+  @doc "The name of the resource, e.g 'posts'"
+  @callback name() :: String.t()
+  @doc "The type of the resource, e.g 'post'"
+  @callback type() :: String.t()
+  @doc "A list of attribute names that make up the primary key, e.g [:class, :group]"
   @callback primary_key() :: [atom]
+  @doc "A list of relationships to other resources"
+  @callback relationships() :: [Ash.relationship()]
+  @doc "A list of actions available for the resource"
+  @callback actions() :: [Ash.action()]
+  @doc "A list of attributes on the resource"
+  @callback attributes() :: [Ash.attribute()]
+  @doc "A list of extensions implemented by the resource"
+  @callback extensions() :: [module]
+  @doc "The data_layer in use by the resource, or nil if there is not one"
+  @callback data_layer() :: module | nil
+  @doc "A description of the resource, to be showed in generated documentation"
+  @callback describe() :: String.t()
+  @doc "A list of authorizers to be used when accessing the resource"
+  @callback authorizers() :: [module]
 
   defmacro __using__(opts) do
     quote do
diff --git a/lib/ash/type/type.ex b/lib/ash/type/type.ex
index 7bc2fac7..4039ad5d 100644
--- a/lib/ash/type/type.ex
+++ b/lib/ash/type/type.ex
@@ -49,12 +49,13 @@ defmodule Ash.Type do
 
   @spec supports_filter?(Ash.resource(), t(), Ash.DataLayer.filter_type(), Ash.data_layer()) ::
           boolean
-  def supports_filter?(resource, type, filter_type, data_layer) when type in @builtin_names do
-    data_layer.can?(resource, {:filter, filter_type}) and filter_type in @builtins[type][:filters]
+  def supports_filter?(resource, type, filter_type, _data_layer) when type in @builtin_names do
+    Ash.data_layer_can?(resource, {:filter, filter_type}) and
+      filter_type in @builtins[type][:filters]
   end
 
   def supports_filter?(resource, type, filter_type, data_layer) do
-    data_layer.can?(resource, {:filter, filter_type}) and
+    Ash.data_layer_can?(resource, {:filter, filter_type}) and
       filter_type in type.supported_filter_types(data_layer)
   end