diff --git a/colorless.cabal b/colorless.cabal
--- a/colorless.cabal
+++ b/colorless.cabal
@@ -3,7 +3,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           colorless
-version:        2.2.8
+version:        2.2.9
 synopsis:       Colorless
 description:    Colorless
 category:       Web
@@ -47,9 +47,11 @@
       Colorless.Endpoint
       Colorless.Imports
       Colorless.Prim
+      Colorless.RuntimeThrower
       Colorless.Server
       Colorless.Server.Exchange
       Colorless.Server.Expr
+      Colorless.ServiceThrower
       Colorless.Types
       Colorless.Val
   default-language: Haskell2010
diff --git a/library/Colorless/Endpoint.hs b/library/Colorless/Endpoint.hs
--- a/library/Colorless/Endpoint.hs
+++ b/library/Colorless/Endpoint.hs
@@ -7,6 +7,7 @@
 import qualified Data.Map as Map
 import qualified Data.HashMap.Lazy as HML
 import Control.Monad.IO.Class (MonadIO(..))
+import Control.Monad.Except
 import Control.Concurrent.Async.Lifted ()
 import Data.Aeson
 import Data.Aeson.Types (parseMaybe)
@@ -15,39 +16,42 @@
 
 import Colorless.Types
 import Colorless.Server.Exchange
+import Colorless.RuntimeThrower
 
 runColorlessSingleton
-  :: (MonadIO m, RuntimeThrower m)
+  :: MonadIO m
   => Version
-  -> (Request -> m Response)
+  -> (Request -> m (Either Response Response))
   -> Value
   -> m Value
 runColorlessSingleton Version{major,minor} handleRequest = runColorless (Map.singleton major (minor, handleRequest))
 
 runColorless
-  :: (MonadIO m, RuntimeThrower m)
-  => Map Major (Minor, Request -> m Response)
+  :: MonadIO m
+  => Map Major (Minor, Request -> m (Either Response Response))
   -> Value
   -> m Value
 runColorless handleRequestMap v = do
-  colorlessVersion <- getColorlessVersion v
-  assertColorlessVersionCompatiability colorlessVersion
-  apiVersion <- getApiVersion v
-  let apiMajor = major apiVersion
-  case Map.lookup apiMajor handleRequestMap of
-    Nothing -> case leastAndGreatest (Map.keys handleRequestMap) of
-      Nothing -> runtimeThrow RuntimeError'NoImplementation
-      Just (minMajor, maxMajor) ->
-        if minMajor > apiMajor
-          then runtimeThrow RuntimeError'ApiMajorVersionTooLow
-          else if maxMajor < apiMajor
-            then runtimeThrow RuntimeError'ApiMajorVersionTooHigh
-            else runtimeThrow RuntimeError'NoImplementation
-    Just (maxMinor, handleRequest) -> if minor apiVersion > maxMinor
-      then runtimeThrow RuntimeError'ApiMinorVersionTooHigh
-      else case parseRequest v of
-        Nothing -> runtimeThrow RuntimeError'UnparsableFormat
-        Just req -> toJSON <$> handleRequest req
+  e <- runExceptT $ do
+    colorlessVersion <- getColorlessVersion v
+    assertColorlessVersionCompatiability colorlessVersion
+    apiVersion <- getApiVersion v
+    let apiMajor = major apiVersion
+    case Map.lookup apiMajor handleRequestMap of
+      Nothing -> case leastAndGreatest (Map.keys handleRequestMap) of
+        Nothing -> runtimeThrow RuntimeError'NoImplementation
+        Just (minMajor, maxMajor) ->
+          if minMajor > apiMajor
+            then runtimeThrow RuntimeError'ApiMajorVersionTooLow
+            else if maxMajor < apiMajor
+              then runtimeThrow RuntimeError'ApiMajorVersionTooHigh
+              else runtimeThrow RuntimeError'NoImplementation
+      Just (maxMinor, handleRequest) -> if minor apiVersion > maxMinor
+        then runtimeThrow RuntimeError'ApiMinorVersionTooHigh
+        else case parseRequest v of
+          Nothing -> runtimeThrow RuntimeError'UnparsableFormat
+          Just req -> toJSON <$> ExceptT (handleRequest req)
+  return $ either toJSON id e
 
 leastAndGreatest :: Ord a => [a] -> Maybe (a,a)
 leastAndGreatest [] = Nothing
diff --git a/library/Colorless/RuntimeThrower.hs b/library/Colorless/RuntimeThrower.hs
new file mode 100644
--- /dev/null
+++ b/library/Colorless/RuntimeThrower.hs
@@ -0,0 +1,17 @@
+module Colorless.RuntimeThrower
+  ( RuntimeThrower(..)
+  ) where
+
+import Control.Monad.Except
+
+import qualified Colorless.Server.Exchange as Server
+import Colorless.Types
+
+class Monad m => RuntimeThrower m where
+  runtimeThrow :: RuntimeError -> m a
+
+instance RuntimeThrower IO where
+  runtimeThrow err = error $ "Runtime error - " ++ show err
+
+instance Monad m => RuntimeThrower (ExceptT Server.Response m) where
+  runtimeThrow = throwError . Server.Response'Error . Server.ResponseError'Runtime
diff --git a/library/Colorless/Server.hs b/library/Colorless/Server.hs
--- a/library/Colorless/Server.hs
+++ b/library/Colorless/Server.hs
@@ -3,9 +3,13 @@
   , module Colorless.Val
   , module Colorless.Server.Expr
   , module Colorless.Server.Exchange
+  , module Colorless.RuntimeThrower
+  , module Colorless.ServiceThrower
   ) where
 
 import Colorless.Val (ToVal(..), FromVal(..), getMember, fromValFromJson, combineObjects)
 import Colorless.Types
 import Colorless.Server.Expr
 import Colorless.Server.Exchange
+import Colorless.RuntimeThrower
+import Colorless.ServiceThrower
diff --git a/library/Colorless/Server/Expr.hs b/library/Colorless/Server/Expr.hs
--- a/library/Colorless/Server/Expr.hs
+++ b/library/Colorless/Server/Expr.hs
@@ -58,6 +58,7 @@
 import Colorless.Ast (Ast(..))
 import Colorless.Val
 import Colorless.Prim
+import Colorless.RuntimeThrower
 
 data EvalConfig m = EvalConfig
   { options :: Options
diff --git a/library/Colorless/ServiceThrower.hs b/library/Colorless/ServiceThrower.hs
new file mode 100644
--- /dev/null
+++ b/library/Colorless/ServiceThrower.hs
@@ -0,0 +1,18 @@
+module Colorless.ServiceThrower
+  ( ServiceThrower(..)
+  ) where
+
+import Control.Monad.Except
+import Data.Aeson
+
+import qualified Colorless.Server.Exchange as Server
+import Colorless.Types
+
+class Monad m => ServiceThrower m where
+  serviceThrow :: Value -> m a
+
+instance ServiceThrower IO where
+  serviceThrow err = error $ "Service error - " ++ show err
+
+instance Monad m => ServiceThrower (ExceptT Server.Response m) where
+  serviceThrow = throwError . Server.Response'Error . Server.ResponseError'Service
diff --git a/library/Colorless/Types.hs b/library/Colorless/Types.hs
--- a/library/Colorless/Types.hs
+++ b/library/Colorless/Types.hs
@@ -6,8 +6,8 @@
   , Pull(..)
   , pullAddress
   , RuntimeError(..)
-  , RuntimeThrower(..)
   , Options(..)
+  , defOptions
   --
   , Symbol(..)
   , Type(..)
@@ -133,15 +133,14 @@
       _ -> mzero
   parseJSON _ = mzero
 
-class Monad m => RuntimeThrower m where
-  runtimeThrow :: RuntimeError -> m a
-
-instance RuntimeThrower IO where
-  runtimeThrow err = error $ "Runtime error - " ++ show err
-
 data Options = Options
   { variableLimit :: Maybe Int
   } deriving (Show, Eq)
+
+defOptions :: Options
+defOptions = Options
+  { variableLimit = Just 100
+  }
 
 --
 
diff --git a/package.yaml b/package.yaml
--- a/package.yaml
+++ b/package.yaml
@@ -1,5 +1,5 @@
 name: colorless
-version: '2.2.8'
+version: '2.2.9'
 category: Web
 synopsis: Colorless
 description: Colorless