diff --git a/morpheus-graphql-app.cabal b/morpheus-graphql-app.cabal
--- a/morpheus-graphql-app.cabal
+++ b/morpheus-graphql-app.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           morpheus-graphql-app
-version:        0.21.0
+version:        0.22.0
 synopsis:       Morpheus GraphQL App
 description:    Build GraphQL APIs with your favourite functional language!
 category:       web, graphql
@@ -21,6 +21,11 @@
     README.md
     changelog.md
 data-files:
+    test/api-constraints/forbidden/query.gql
+    test/api-constraints/over-limit/query.gql
+    test/api-constraints/schema.gql
+    test/api-constraints/success/query.gql
+    test/api-constraints/under-limit/query.gql
     test/api/deity/interface/query.gql
     test/api/deity/schema.gql
     test/api/deity/simple/query.gql
@@ -57,6 +62,10 @@
     test/named-resolvers/realm-simple/query.gql
     test/named-resolvers/realms.gql
     test/named-resolvers/realms/query.gql
+    test/api-constraints/forbidden/response.json
+    test/api-constraints/over-limit/response.json
+    test/api-constraints/success/response.json
+    test/api-constraints/under-limit/response.json
     test/api/deity/interface/response.json
     test/api/deity/resolvers.json
     test/api/deity/simple/response.json
@@ -123,7 +132,7 @@
     , containers >=0.4.2.1 && <0.7.0
     , hashable >=1.0.0 && <2.0.0
     , megaparsec >=7.0.0 && <10.0.0
-    , morpheus-graphql-core >=0.21.0 && <0.22.0
+    , morpheus-graphql-core >=0.22.0 && <0.23.0
     , mtl >=2.0.0 && <3.0.0
     , relude >=0.3.0 && <2.0.0
     , scientific >=0.3.6.2 && <0.4.0
@@ -139,6 +148,7 @@
   type: exitcode-stdio-1.0
   main-is: Spec.hs
   other-modules:
+      APIConstraints
       NamedResolvers
       Paths_morpheus_graphql_app
   hs-source-dirs:
@@ -153,8 +163,8 @@
     , hashable >=1.0.0 && <2.0.0
     , megaparsec >=7.0.0 && <10.0.0
     , morpheus-graphql-app
-    , morpheus-graphql-core >=0.21.0 && <0.22.0
-    , morpheus-graphql-tests >=0.21.0 && <0.22.0
+    , morpheus-graphql-core >=0.22.0 && <0.23.0
+    , morpheus-graphql-tests >=0.22.0 && <0.23.0
     , mtl >=2.0.0 && <3.0.0
     , relude >=0.3.0 && <2.0.0
     , scientific >=0.3.6.2 && <0.4.0
diff --git a/src/Data/Morpheus/App.hs b/src/Data/Morpheus/App.hs
--- a/src/Data/Morpheus/App.hs
+++ b/src/Data/Morpheus/App.hs
@@ -19,9 +19,12 @@
     runAppStream,
     MapAPI (..),
     eitherSchema,
+    withConstraint,
+    APIConstraint,
   )
 where
 
+import Control.Monad.Except (throwError)
 import qualified Data.Aeson as A
 import Data.ByteString.Lazy (ByteString)
 import Data.Morpheus.App.Internal.Resolving
@@ -45,7 +48,7 @@
     parseRequestWith,
     render,
   )
-import Data.Morpheus.Internal.Ext ((<:>))
+import Data.Morpheus.Internal.Ext (GQLResult, (<:>))
 import Data.Morpheus.Internal.Utils
   ( empty,
     prop,
@@ -75,7 +78,7 @@
 mkApp appSchema appResolvers =
   resultOr
     FailApp
-    (App . AppData defaultConfig appResolvers)
+    (App . AppData defaultConfig [] appResolvers)
     (validateSchema True defaultConfig appSchema)
 
 data App event (m :: Type -> Type)
@@ -92,8 +95,11 @@
   App {} <> FailApp {appErrors} = FailApp appErrors
   (App x) <> (App y) = resultOr FailApp App (stitch x y)
 
+type APIConstraint = Schema VALID -> Operation VALID -> Either String ()
+
 data AppData event (m :: Type -> Type) s = AppData
   { appConfig :: Config,
+    constraints :: [APIConstraint],
     appResolvers :: RootResolverValue event m,
     appSchema :: Schema s
   }
@@ -103,33 +109,44 @@
 
 instance Monad m => Stitching (AppData e m s) where
   stitch x y =
-    AppData (appConfig y)
+    AppData
+      (appConfig y)
+      (constraints x <> constraints y)
       <$> prop stitch appResolvers x y
       <*> prop stitch appSchema x y
 
+checkConstraints :: Schema VALID -> Operation VALID -> [APIConstraint] -> GQLResult ()
+checkConstraints appSchema validRequest constraints =
+  either
+    (throwError . fromString . ("API Constraint: " <>))
+    (const $ pure ())
+    (traverse (\f -> f appSchema validRequest) constraints)
+
 runAppData ::
   (Monad m, ValidateSchema s) =>
   AppData event m s ->
   GQLRequest ->
   ResponseStream event m (Value VALID)
-runAppData AppData {appConfig, appSchema, appResolvers} request = do
-  validRequest <- validateReq appSchema appConfig request
+runAppData AppData {appConfig, appSchema, appResolvers, constraints} request = do
+  validRequest <- validateReq constraints appSchema appConfig request
   runRootResolverValue appResolvers validRequest
 
 validateReq ::
   ( Monad m,
     ValidateSchema s
   ) =>
+  [APIConstraint] ->
   Schema s ->
   Config ->
   GQLRequest ->
   ResponseStream event m ResolverContext
-validateReq inputSchema config request = ResultT $
+validateReq constraints inputSchema config request = ResultT $
   pure $
     do
       validSchema <- validateSchema True config inputSchema
       schema <- internalSchema <:> validSchema
       operation <- parseRequestWith config validSchema request
+      checkConstraints schema operation constraints
       pure
         ( [],
           ResolverContext
@@ -171,10 +188,20 @@
 runApp :: (MapAPI a b, Monad m) => App e m -> a -> m b
 runApp app = mapAPI (stateless . runAppStream app)
 
+mapApp :: (AppData e m VALID -> AppData e m VALID) -> App e m -> App e m
+mapApp f App {app} =
+  App {app = f app}
+mapApp _ x = x
+
 withDebugger :: App e m -> App e m
-withDebugger App {app = AppData {appConfig = Config {..}, ..}} =
-  App {app = AppData {appConfig = Config {debug = True, ..}, ..}, ..}
-withDebugger x = x
+withDebugger = mapApp f
+  where
+    f AppData {appConfig = Config {..}, ..} = AppData {appConfig = Config {debug = True, ..}, ..}
+
+withConstraint :: APIConstraint -> App e m -> App e m
+withConstraint constraint = mapApp f
+  where
+    f AppData {..} = AppData {constraints = constraint : constraints, ..}
 
 eitherSchema :: App event m -> Either [GQLError] ByteString
 eitherSchema (App AppData {appSchema}) = Right (render appSchema)
diff --git a/src/Data/Morpheus/App/Internal/Resolving/Resolver.hs b/src/Data/Morpheus/App/Internal/Resolving/Resolver.hs
--- a/src/Data/Morpheus/App/Internal/Resolving/Resolver.hs
+++ b/src/Data/Morpheus/App/Internal/Resolving/Resolver.hs
@@ -175,6 +175,7 @@
 -- Using the 'ResolverContext' itself is unsafe because it exposes internal structures
 -- of the AST, but you can use the "Data.Morpheus.Types.SelectionTree" typeClass to manipulate
 -- the internal AST with a safe interface.
+{-# DEPRECATED unsafeInternalContext "use asks" #-}
 unsafeInternalContext :: (Monad m, LiftOperation o) => Resolver o e m ResolverContext
 unsafeInternalContext = ask
 
diff --git a/src/Data/Morpheus/App/Internal/Stitching.hs b/src/Data/Morpheus/App/Internal/Stitching.hs
--- a/src/Data/Morpheus/App/Internal/Stitching.hs
+++ b/src/Data/Morpheus/App/Internal/Stitching.hs
@@ -31,7 +31,8 @@
     prop,
   )
 import Data.Morpheus.Types.Internal.AST
-  ( Directives,
+  ( DirectiveDefinition,
+    Directives,
     DirectivesDefinition,
     FieldDefinition,
     FieldsDefinition,
@@ -74,7 +75,7 @@
   stitch x y = runResolutionT (mergeT x y) unsafeFromList (resolveWith stitch)
 
 instance Stitching (DirectivesDefinition s) where
-  stitch = merge
+  stitch x y = runResolutionT (mergeT x y) unsafeFromList (resolveWith stitch)
 
 instance Stitching (Directives s) where
   stitch = merge
@@ -95,6 +96,11 @@
     <*> prop fstM typeName x y
     <*> prop stitch typeDirectives x y
     <*> prop stitch typeContent x y
+
+instance Stitching (DirectiveDefinition s) where
+  stitch x y
+    | x == y = pure x
+    | otherwise = throwError "only directives with same structure can be merged"
 
 instance Stitching (TypeDefinition cat s) where
   stitch x y =
diff --git a/src/Data/Morpheus/App/RenderIntrospection.hs b/src/Data/Morpheus/App/RenderIntrospection.hs
--- a/src/Data/Morpheus/App/RenderIntrospection.hs
+++ b/src/Data/Morpheus/App/RenderIntrospection.hs
@@ -19,7 +19,6 @@
 import Data.Morpheus.App.Internal.Resolving.Resolver
   ( Resolver,
     ResolverContext (..),
-    unsafeInternalContext,
   )
 import Data.Morpheus.App.Internal.Resolving.Types
   ( ResolverValue,
@@ -86,7 +85,7 @@
   getSchema :: m (Schema VALID)
 
 instance Monad m => WithSchema (Resolver QUERY e m) where
-  getSchema = schema <$> unsafeInternalContext
+  getSchema = schema <$> ask
 
 selectType ::
   WithSchema m =>
diff --git a/test/APIConstraints.hs b/test/APIConstraints.hs
new file mode 100644
--- /dev/null
+++ b/test/APIConstraints.hs
@@ -0,0 +1,83 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE NoImplicitPrelude #-}
+
+module APIConstraints
+  ( runAPIConstraints,
+  )
+where
+
+import Data.Aeson (Value (..))
+import qualified Data.ByteString.Lazy.Char8 as LBS
+import Data.Morpheus.App
+  ( APIConstraint,
+    App,
+    mkApp,
+    runApp,
+    withConstraint,
+  )
+import Data.Morpheus.App.Internal.Resolving (resultOr)
+import Data.Morpheus.App.NamedResolvers
+  ( RootResolverValue,
+    object,
+    queryResolvers,
+  )
+import Data.Morpheus.Core
+  ( parseSchema,
+  )
+import Data.Morpheus.Types.IO
+  ( GQLRequest,
+    GQLResponse,
+  )
+import Data.Morpheus.Types.Internal.AST
+  ( Schema,
+    VALID,
+  )
+import Data.Morpheus.Types.SelectionTree
+  ( SelectionTree (..),
+  )
+import Relude hiding (ByteString)
+import Test.Morpheus
+  ( FileUrl,
+    testApi,
+  )
+import Test.Tasty
+  ( TestTree,
+  )
+
+resolvers :: Monad m => RootResolverValue e m
+resolvers =
+  queryResolvers
+    [ ( "Query",
+        const $
+          object
+            [ ("success", pure "success"),
+              ("forbidden", pure "forbidden!"),
+              ("limited", pure "num <= 5")
+            ]
+      )
+    ]
+
+getSchema :: String -> IO (Schema VALID)
+getSchema url = LBS.readFile url >>= resultOr (fail . show) pure . parseSchema
+
+getApp :: FileUrl -> IO (App e IO)
+getApp _ = (`mkApp` resolvers) <$> getSchema "test/api-constraints/schema.gql"
+
+forbidden :: APIConstraint
+forbidden _ query
+  | hasChild ("forbidden" :: String) query = Left "no forbidden field!"
+  | otherwise = Right ()
+
+max5 :: APIConstraint
+max5 _ query =
+  case getChild ("limited" :: Text) query >>= getArgument ("num" :: Text) of
+    Just (Number n) | n > 5 -> Left ("num " <> show n <> " is greater then 5! but found ")
+    _ -> pure ()
+
+runAPIConstraints :: FileUrl -> FileUrl -> TestTree
+runAPIConstraints url = testApi api
+  where
+    api :: GQLRequest -> IO GQLResponse
+    api req = do
+      app <- withConstraint max5 . withConstraint forbidden <$> getApp url
+      runApp app req
diff --git a/test/Spec.hs b/test/Spec.hs
--- a/test/Spec.hs
+++ b/test/Spec.hs
@@ -7,6 +7,7 @@
   )
 where
 
+import APIConstraints (runAPIConstraints)
 import Data.Morpheus.App
   ( App (..),
     eitherSchema,
@@ -62,5 +63,6 @@
     "App Tests"
     [ deepScan runMergeTest (mkUrl "merge"),
       deepScan runApiTest (mkUrl "api"),
-      deepScan (map . runNamedResolversTest) (mkUrl "named-resolvers")
+      deepScan (map . runNamedResolversTest) (mkUrl "named-resolvers"),
+      deepScan (map . runAPIConstraints) (mkUrl "api-constraints")
     ]
diff --git a/test/api-constraints/forbidden/query.gql b/test/api-constraints/forbidden/query.gql
new file mode 100644
--- /dev/null
+++ b/test/api-constraints/forbidden/query.gql
@@ -0,0 +1,3 @@
+query {
+  forbidden
+}
diff --git a/test/api-constraints/forbidden/response.json b/test/api-constraints/forbidden/response.json
new file mode 100644
--- /dev/null
+++ b/test/api-constraints/forbidden/response.json
@@ -0,0 +1,7 @@
+{
+  "errors": [
+    {
+      "message": "API Constraint: no forbidden field!"
+    }
+  ]
+}
diff --git a/test/api-constraints/over-limit/query.gql b/test/api-constraints/over-limit/query.gql
new file mode 100644
--- /dev/null
+++ b/test/api-constraints/over-limit/query.gql
@@ -0,0 +1,3 @@
+query {
+  limited(num: 7)
+}
diff --git a/test/api-constraints/over-limit/response.json b/test/api-constraints/over-limit/response.json
new file mode 100644
--- /dev/null
+++ b/test/api-constraints/over-limit/response.json
@@ -0,0 +1,7 @@
+{
+  "errors": [
+    {
+      "message": "API Constraint: num 7.0 is greater then 5! but found "
+    }
+  ]
+}
diff --git a/test/api-constraints/schema.gql b/test/api-constraints/schema.gql
new file mode 100644
--- /dev/null
+++ b/test/api-constraints/schema.gql
@@ -0,0 +1,5 @@
+type Query {
+  success: String
+  forbidden: String
+  limited(num: Int): String
+}
diff --git a/test/api-constraints/success/query.gql b/test/api-constraints/success/query.gql
new file mode 100644
--- /dev/null
+++ b/test/api-constraints/success/query.gql
@@ -0,0 +1,3 @@
+query {
+  success
+}
diff --git a/test/api-constraints/success/response.json b/test/api-constraints/success/response.json
new file mode 100644
--- /dev/null
+++ b/test/api-constraints/success/response.json
@@ -0,0 +1,5 @@
+{
+  "data": {
+    "success": "success"
+  }
+}
diff --git a/test/api-constraints/under-limit/query.gql b/test/api-constraints/under-limit/query.gql
new file mode 100644
--- /dev/null
+++ b/test/api-constraints/under-limit/query.gql
@@ -0,0 +1,3 @@
+query {
+  limited(num: 4)
+}
diff --git a/test/api-constraints/under-limit/response.json b/test/api-constraints/under-limit/response.json
new file mode 100644
--- /dev/null
+++ b/test/api-constraints/under-limit/response.json
@@ -0,0 +1,5 @@
+{
+  "data": {
+    "limited": "num <= 5"
+  }
+}