diff --git a/ChangeLog.md b/ChangeLog.md
index 68d001175..be5a7add6 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,5 +1,9 @@
 # Revision history for haskell-lsp
 
+## 0.9.0.0
+
+* Add `MarkupContent` to `HoverResponse`, and (some) json roundtrip tests.
+
 ## 0.8.2.0 -- 2019-04-11
 
 * Add `applyTextEdit` and `editTextEdit` helpers
diff --git a/example/Main.hs b/example/Main.hs
index cf7667c6a..c99151d78 100644
--- a/example/Main.hs
+++ b/example/Main.hs
@@ -238,7 +238,7 @@ reactor lf inp = do
 
         let
           ht = Just $ J.Hover ms (Just range)
-          ms = J.List [J.CodeString $ J.LanguageString "lsp-hello" "TYPE INFO" ]
+          ms = J.HoverContentsMS $ J.List [J.CodeString $ J.LanguageString "lsp-hello" "TYPE INFO" ]
           range = J.Range pos pos
         reactorSend $ RspHover $ Core.makeResponseMessage req ht
 
diff --git a/haskell-lsp-types/ChangeLog.md b/haskell-lsp-types/ChangeLog.md
index 34f4e035d..aafe65116 100644
--- a/haskell-lsp-types/ChangeLog.md
+++ b/haskell-lsp-types/ChangeLog.md
@@ -1,5 +1,9 @@
 # Revision history for haskell-lsp-types
 
+## 0.8.3.0
+
+* Add `MarkupContent` to `HoverResponse`, and (some) json roundtrip tests.
+
 ## 0.8.2.0 -- 2019-04-11
 
 * Add `applyTextEdit` and `editTextEdit` helpers
diff --git a/haskell-lsp-types/haskell-lsp-types.cabal b/haskell-lsp-types/haskell-lsp-types.cabal
index ec5f16973..4a1b85901 100644
--- a/haskell-lsp-types/haskell-lsp-types.cabal
+++ b/haskell-lsp-types/haskell-lsp-types.cabal
@@ -1,5 +1,5 @@
 name:                haskell-lsp-types
-version:             0.8.2.0
+version:             0.9.0.0
 synopsis:            Haskell library for the Microsoft Language Server Protocol, data types
 
 description:         An implementation of the types to allow language implementors to
diff --git a/haskell-lsp-types/src/Language/Haskell/LSP/Types/DataTypesJSON.hs b/haskell-lsp-types/src/Language/Haskell/LSP/Types/DataTypesJSON.hs
index 7fd2d965e..a1d05e86e 100644
--- a/haskell-lsp-types/src/Language/Haskell/LSP/Types/DataTypesJSON.hs
+++ b/haskell-lsp-types/src/Language/Haskell/LSP/Types/DataTypesJSON.hs
@@ -5,7 +5,6 @@
 {-# LANGUAGE FlexibleInstances          #-}
 {-# LANGUAGE FunctionalDependencies     #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
-{-# LANGUAGE MultiParamTypeClasses      #-}
 {-# LANGUAGE OverloadedStrings          #-}
 {-# LANGUAGE TemplateHaskell            #-}
 {-# LANGUAGE TypeSynonymInstances       #-}
@@ -18,14 +17,15 @@ import           Data.Aeson.TH
 import           Data.Aeson.Types
 import           Data.Text                                  (Text)
 import qualified Data.Text                                  as T
+import           Language.Haskell.LSP.Types.ClientCapabilities
 import           Language.Haskell.LSP.Types.Command
 import           Language.Haskell.LSP.Types.Constants
-import           Language.Haskell.LSP.Types.ClientCapabilities
 import           Language.Haskell.LSP.Types.Diagnostic
 import           Language.Haskell.LSP.Types.DocumentFilter
 import           Language.Haskell.LSP.Types.List
-import           Language.Haskell.LSP.Types.Message
 import           Language.Haskell.LSP.Types.Location
+import           Language.Haskell.LSP.Types.MarkupContent
+import           Language.Haskell.LSP.Types.Message
 import           Language.Haskell.LSP.Types.Symbol
 import           Language.Haskell.LSP.Types.TextDocument
 import           Language.Haskell.LSP.Types.Uri
@@ -499,7 +499,7 @@ interface ServerCapabilities {
          *
          * Since 3.10.0
          */
-        foldingRangeProvider?: boolean | FoldingRangeProviderOptions | (FoldingRangeProviderOptions & TextDocumentRegistrationOptions & StaticRegistrationOptions);     
+        foldingRangeProvider?: boolean | FoldingRangeProviderOptions | (FoldingRangeProviderOptions & TextDocumentRegistrationOptions & StaticRegistrationOptions);
         /**
          * The server provides execute command support.
          */
@@ -544,7 +544,7 @@ data TDS = TDSOptions TextDocumentSyncOptions
 
 instance FromJSON TDS where
     parseJSON x = TDSOptions <$> parseJSON x <|> TDSKind <$> parseJSON x
-    
+
 instance ToJSON TDS where
     toJSON (TDSOptions x) = toJSON x
     toJSON (TDSKind x) = toJSON x
@@ -553,7 +553,7 @@ data GotoOptions = GotoOptionsStatic Bool
                  | GotoOptionsDynamic
                     { -- | A document selector to identify the scope of the registration. If set to null
                       -- the document selector provided on the client side will be used.
-                      _documentSelector :: Maybe DocumentSelector 
+                      _documentSelector :: Maybe DocumentSelector
                       -- | The id used to register the request. The id can be used to deregister
                       -- the request again. See also Registration#id.
                     , _id :: Maybe Text
@@ -624,7 +624,7 @@ data WorkspaceOptions =
   deriving (Show, Read, Eq)
 
 deriveJSON lspOptions ''WorkspaceOptions
-      
+
 data InitializeResponseCapabilitiesInner =
   InitializeResponseCapabilitiesInner
     { -- | Defines how text documents are synced. Is either a detailed structure
@@ -1232,19 +1232,19 @@ Request:
 method: ‘workspace/configuration’
 params: ConfigurationParams defined as follows
 export interface ConfigurationParams {
-	items: ConfigurationItem[];
+        items: ConfigurationItem[];
 }
 
 export interface ConfigurationItem {
-	/**
-	 * The scope to get the configuration section for.
-	 */
-	scopeUri?: string;
-
-	/**
-	 * The configuration section asked for.
-	 */
-	section?: string;
+        /**
+         * The scope to get the configuration section for.
+         */
+        scopeUri?: string;
+
+        /**
+         * The configuration section asked for.
+         */
+        section?: string;
 }
 Response:
 
@@ -1731,26 +1731,28 @@ Response
 
     result: Hover | null defined as follows:
 
+
 /**
- * The result of a hove request.
+ * The result of a hover request.
  */
 interface Hover {
-    /**
-     * The hover's content
-     */
-    contents: MarkedString | MarkedString[];
+        /**
+         * The hover's content
+         */
+        contents: MarkedString | MarkedString[] | MarkupContent;
 
-    /**
-     * An optional range
-     */
-    range?: Range;
+        /**
+         * An optional range is a range inside a text document
+         * that is used to visualize a hover, e.g. by changing the background color.
+         */
+        range?: Range;
 }
 
-Where MarkedString is defined as follows:
+
 /**
  * MarkedString can be used to render human readable text. It is either a markdown string
  * or a code-block that provides a language and a code snippet. The language identifier
- * is sematically equal to the optional language identifier in fenced code blocks in GitHub
+ * is semantically equal to the optional language identifier in fenced code blocks in GitHub
  * issues. See https://help.github.com/articles/creating-and-highlighting-code-blocks/#syntax-highlighting
  *
  * The pair of a language and a value is an equivalent to markdown:
@@ -1759,7 +1761,8 @@ Where MarkedString is defined as follows:
  * ```
  *
  * Note that markdown strings will be sanitized - that means html will be escaped.
- */
+* @deprecated use MarkupContent instead.
+*/
 type MarkedString = string | { language: string; value: string };
 
     error: code and message set in case an exception happens during the hover
@@ -1777,6 +1780,7 @@ data LanguageString =
 
 deriveJSON lspOptions ''LanguageString
 
+{-# DEPRECATED MarkedString, PlainString, CodeString "Use MarkupContent instead, since 3.3.0 (11/24/2017)" #-}
 data MarkedString =
     PlainString T.Text
   | CodeString LanguageString
@@ -1789,9 +1793,52 @@ instance FromJSON MarkedString where
   parseJSON (A.String t) = pure $ PlainString t
   parseJSON o            = CodeString <$> parseJSON o
 
+-- -------------------------------------
+
+data HoverContents =
+    HoverContentsMS (List MarkedString)
+  | HoverContents   MarkupContent
+  | HoverContentsEmpty
+  deriving (Read,Show,Eq)
+
+instance ToJSON HoverContents where
+  toJSON (HoverContentsMS  x) = toJSON x
+  toJSON (HoverContents    x) = toJSON x
+  toJSON (HoverContentsEmpty) = A.Null
+instance FromJSON HoverContents where
+  parseJSON v@(A.String _) = HoverContentsMS <$> parseJSON v
+  parseJSON   (A.Null)     = pure HoverContentsEmpty
+  parseJSON v@(A.Array _)  = HoverContentsMS <$> parseJSON v
+  parseJSON v@(A.Object _) = HoverContents   <$> parseJSON v
+                         <|> HoverContentsMS <$> parseJSON v
+  parseJSON _ = mempty
+
+-- -------------------------------------
+
+#if __GLASGOW_HASKELL__ >= 804
+instance Semigroup HoverContents where
+  (<>) = mappend
+#endif
+
+instance Monoid HoverContents where
+  mempty = HoverContentsEmpty
+
+  HoverContentsEmpty `mappend` hc = hc
+  hc `mappend` HoverContentsEmpty = hc
+  HoverContents h1   `mappend` HoverContents         h2   = HoverContents (h1 `mappend` h2)
+  HoverContents h1   `mappend` HoverContentsMS (List h2s) = HoverContents (mconcat (h1: (map toMarkupContent h2s)))
+  HoverContentsMS (List h1s) `mappend` HoverContents         h2    = HoverContents (mconcat ((map toMarkupContent h1s) ++ [h2]))
+  HoverContentsMS (List h1s) `mappend` HoverContentsMS (List h2s) = HoverContentsMS (List (h1s `mappend` h2s))
+
+toMarkupContent :: MarkedString -> MarkupContent
+toMarkupContent (PlainString s) = unmarkedUpContent s
+toMarkupContent (CodeString (LanguageString lang s)) = markedUpContent lang s
+
+-- -------------------------------------
+
 data Hover =
   Hover
-    { _contents :: List MarkedString
+    { _contents :: HoverContents
     , _range    :: Maybe Range
     } deriving (Read,Show,Eq)
 
@@ -2852,4 +2899,3 @@ data TraceNotification =
   } deriving (Show, Read, Eq)
 
 deriveJSON lspOptions ''TraceNotification
-
diff --git a/haskell-lsp-types/src/Language/Haskell/LSP/Types/MarkupContent.hs b/haskell-lsp-types/src/Language/Haskell/LSP/Types/MarkupContent.hs
index 03f3538a7..46e5d97de 100644
--- a/haskell-lsp-types/src/Language/Haskell/LSP/Types/MarkupContent.hs
+++ b/haskell-lsp-types/src/Language/Haskell/LSP/Types/MarkupContent.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP                        #-}
 {-# LANGUAGE DuplicateRecordFields      #-}
 {-# LANGUAGE OverloadedStrings          #-}
 {-# LANGUAGE TemplateHaskell            #-}
@@ -11,6 +12,7 @@ module Language.Haskell.LSP.Types.MarkupContent where
 
 import           Data.Aeson
 import           Data.Aeson.TH
+import           Data.Semigroup
 import           Data.Text                                      (Text)
 import           Language.Haskell.LSP.Types.Constants
 
@@ -23,15 +25,15 @@ import           Language.Haskell.LSP.Types.Constants
  * are reserved for internal usage.
  */
 export namespace MarkupKind {
-	/**
-	 * Plain text is supported as a content format
-	 */
-	export const PlainText: 'plaintext' = 'plaintext';
-
-	/**
-	 * Markdown is supported as a content format
-	 */
-	export const Markdown: 'markdown' = 'markdown';
+        /**
+         * Plain text is supported as a content format
+         */
+        export const PlainText: 'plaintext' = 'plaintext';
+
+        /**
+         * Markdown is supported as a content format
+         */
+        export const Markdown: 'markdown' = 'markdown';
 }
 export type MarkupKind = 'plaintext' | 'markdown';
 -}
@@ -78,15 +80,15 @@ instance FromJSON MarkupKind where
  * remove HTML from the markdown to avoid script execution.
  */
 export interface MarkupContent {
-	/**
-	 * The type of the Markup
-	 */
-	kind: MarkupKind;
-
-	/**
-	 * The content itself
-	 */
-	value: string;
+        /**
+         * The type of the Markup
+         */
+        kind: MarkupKind;
+
+        /**
+         * The content itself
+         */
+        value: string;
 }
 -}
 
@@ -120,3 +122,37 @@ data MarkupContent =
   deriving (Read, Show, Eq)
 
 deriveJSON lspOptions ''MarkupContent
+
+-- ---------------------------------------------------------------------
+
+-- | Create a 'MarkupContent' containing a quoted language string only.
+markedUpContent :: Text -> Text -> MarkupContent
+markedUpContent lang quote
+ = MarkupContent MkMarkdown ("```" <> lang <> "\n" <> quote <> "\n```\n")
+
+-- ---------------------------------------------------------------------
+
+-- | Create a 'MarkupContent' containing unquoted text
+unmarkedUpContent :: Text -> MarkupContent
+unmarkedUpContent str = MarkupContent MkPlainText str
+
+-- ---------------------------------------------------------------------
+
+-- | Markdown for a section separator in Markdown, being a horizontal line
+sectionSeparator :: Text
+sectionSeparator = "*\t*\t*\n"
+
+-- ---------------------------------------------------------------------
+
+#if __GLASGOW_HASKELL__ >= 804
+instance Semigroup MarkupContent where
+  (<>) = mappend
+#endif
+
+instance Monoid MarkupContent where
+  mempty = MarkupContent MkPlainText ""
+  MarkupContent MkPlainText s1 `mappend` MarkupContent MkPlainText s2 = MarkupContent MkPlainText (s1 `mappend` s2)
+  MarkupContent MkMarkdown  s1 `mappend` MarkupContent _           s2 = MarkupContent MkMarkdown  (s1 `mappend` s2)
+  MarkupContent _           s1 `mappend` MarkupContent MkMarkdown  s2 = MarkupContent MkMarkdown  (s1 `mappend` s2)
+
+-- ---------------------------------------------------------------------
diff --git a/haskell-lsp.cabal b/haskell-lsp.cabal
index 0dd464192..b0e32c3f2 100644
--- a/haskell-lsp.cabal
+++ b/haskell-lsp.cabal
@@ -1,5 +1,5 @@
 name:                haskell-lsp
-version:             0.8.2.0
+version:             0.9.0.0
 synopsis:            Haskell library for the Microsoft Language Server Protocol
 
 description:         An implementation of the types, and basic message server to
@@ -44,7 +44,7 @@ library
                      , filepath
                      , hslogger
                      , hashable
-                     , haskell-lsp-types >= 0.8
+                     , haskell-lsp-types >= 0.8.3
                      , lens >= 4.15.2
                      , mtl
                      , network-uri
@@ -94,30 +94,34 @@ test-suite haskell-lsp-test
   main-is:             Main.hs
   other-modules:       Spec
                        CapabilitiesSpec
+                       JsonSpec
                        DiagnosticsSpec
                        MethodSpec
                        ServerCapabilitiesSpec
+                       TypesSpec
                        URIFilePathSpec
                        VspSpec
                        WorkspaceEditSpec
                        WorkspaceFoldersSpec
   build-depends:       base
+                     , QuickCheck
                      , aeson
                      , bytestring
                      , containers
                      , data-default
                      , directory
                      , filepath
-                     , hspec
                      , hashable
+                     , haskell-lsp
+                     , hspec
                      -- , hspec-jenkins
                      , lens >= 4.15.2
                      , network-uri
+                     , quickcheck-instances
                      , sorted-list == 0.2.1.*
-                     , yi-rope
-                     , haskell-lsp
-                     , text
                      , stm
+                     , text
+                     , yi-rope
   ghc-options:         -threaded -rtsopts -with-rtsopts=-N -Wall
   default-language:    Haskell2010
 
diff --git a/test/JsonSpec.hs b/test/JsonSpec.hs
new file mode 100644
index 000000000..a69b8d3a3
--- /dev/null
+++ b/test/JsonSpec.hs
@@ -0,0 +1,71 @@
+{-# LANGUAGE DataKinds            #-}
+{-# LANGUAGE FlexibleInstances    #-}
+{-# LANGUAGE OverloadedStrings    #-}
+{-# LANGUAGE TypeSynonymInstances #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+-- | Test for JSON serialization
+module JsonSpec where
+
+import           Language.Haskell.LSP.Types
+
+import           Data.Aeson
+import           Test.Hspec
+import           Test.Hspec.QuickCheck
+import           Test.QuickCheck               hiding (Success)
+import           Test.QuickCheck.Instances     ()
+
+-- import Debug.Trace
+-- ---------------------------------------------------------------------
+
+{-# ANN module ("HLint: ignore Redundant do"       :: String) #-}
+
+main :: IO ()
+main = hspec spec
+
+spec :: Spec
+spec = describe "dispatcher" jsonSpec
+
+-- ---------------------------------------------------------------------
+
+jsonSpec :: Spec
+jsonSpec = do
+  describe "General JSON instances round trip" $ do
+  -- DataTypesJSON
+    prop "LanguageString"    (propertyJsonRoundtrip :: LanguageString -> Bool)
+    prop "MarkedString"      (propertyJsonRoundtrip :: MarkedString -> Bool)
+    prop "MarkupContent"     (propertyJsonRoundtrip :: MarkupContent -> Bool)
+    prop "HoverContents"     (propertyJsonRoundtrip :: HoverContents -> Bool)
+
+
+-- ---------------------------------------------------------------------
+
+propertyJsonRoundtrip :: (Eq a, ToJSON a, FromJSON a) => a -> Bool
+propertyJsonRoundtrip a = Success a == fromJSON (toJSON a)
+
+-- ---------------------------------------------------------------------
+
+instance Arbitrary LanguageString where
+  arbitrary = LanguageString <$> arbitrary <*> arbitrary
+
+instance Arbitrary MarkedString where
+  arbitrary = oneof [PlainString <$> arbitrary, CodeString <$> arbitrary]
+
+instance Arbitrary MarkupContent where
+  arbitrary = MarkupContent <$> arbitrary <*> arbitrary
+
+instance Arbitrary MarkupKind where
+  arbitrary = oneof [pure MkPlainText,pure MkMarkdown]
+
+instance Arbitrary HoverContents where
+  arbitrary = oneof [ HoverContentsMS <$> arbitrary
+                    , HoverContents <$> arbitrary
+                    , pure HoverContentsEmpty]
+
+-- | make lists of maximum length 3 for test performance
+smallList :: Gen a -> Gen [a]
+smallList = resize 3 . listOf
+
+instance (Arbitrary a) => Arbitrary (List a) where
+  arbitrary = List <$> arbitrary
+
+-- ---------------------------------------------------------------------
diff --git a/test/ServerCapabilitiesSpec.hs b/test/ServerCapabilitiesSpec.hs
index 2f2142b4b..6f4790d13 100644
--- a/test/ServerCapabilitiesSpec.hs
+++ b/test/ServerCapabilitiesSpec.hs
@@ -24,7 +24,7 @@ spec = describe "server capabilities" $ do
     describe "encodes" $
       it "just id" $
         encode (FoldingRangeOptionsDynamicDocument Nothing (Just "foo")) `shouldBe` "{\"id\":\"foo\"}"
-  it "decodes" $ 
+  it "decodes" $
     let input = "{\"hoverProvider\": true, \"colorProvider\": {\"id\": \"abc123\", \"documentSelector\": " <> documentFiltersJson <> "}}"
         Just caps = decode input :: Maybe InitializeResponseCapabilitiesInner
       in caps ^. colorProvider `shouldBe` Just (ColorOptionsDynamicDocument (Just documentFilters) (Just "abc123"))
diff --git a/test/TypesSpec.hs b/test/TypesSpec.hs
new file mode 100644
index 000000000..42b473986
--- /dev/null
+++ b/test/TypesSpec.hs
@@ -0,0 +1,31 @@
+{-# LANGUAGE OverloadedStrings #-}
+module TypesSpec where
+
+import           Data.Monoid
+import qualified Language.Haskell.LSP.Types as J
+import           Test.Hspec
+
+-- ---------------------------------------------------------------------
+
+main :: IO ()
+main = hspec spec
+
+spec :: Spec
+spec = diagnosticsSpec
+
+-- ---------------------------------------------------------------------
+
+diagnosticsSpec :: Spec
+diagnosticsSpec = do
+  describe "MarkupContent" $ do
+    it "appends two plainstrings" $ do
+      J.unmarkedUpContent "string1\n" <> J.unmarkedUpContent "string2\n"
+        `shouldBe` J.unmarkedUpContent "string1\nstring2\n"
+    it "appends a marked up and a plain string" $ do
+      J.markedUpContent "haskell" "foo :: Int" <> J.unmarkedUpContent "string2\n"
+        `shouldBe` J.MarkupContent J.MkMarkdown "```haskell\nfoo :: Int\n```\nstring2\n"
+    it "appends a plain string and a marked up string" $ do
+       J.unmarkedUpContent "string2\n" <> J.markedUpContent "haskell" "foo :: Int"
+        `shouldBe` J.MarkupContent J.MkMarkdown "string2\n```haskell\nfoo :: Int\n```\n"
+
+-- ---------------------------------------------------------------------
diff --git a/test/WorkspaceEditSpec.hs b/test/WorkspaceEditSpec.hs
index 481ca7994..1ae19002c 100644
--- a/test/WorkspaceEditSpec.hs
+++ b/test/WorkspaceEditSpec.hs
@@ -20,6 +20,6 @@ spec = do
   describe "editTextEdit" $
     it "edits a multiline text edit" $
       let orig = TextEdit (Range (Position 1 1) (Position 2 2)) "hello\nworld"
-          inner = TextEdit (Range (Position 0 3) (Position 1 3)) "ios\ngo" 
+          inner = TextEdit (Range (Position 0 3) (Position 1 3)) "ios\ngo"
           expected = TextEdit (Range (Position 1 1) (Position 2 2)) "helios\ngold"
          in editTextEdit orig inner `shouldBe` expected
diff --git a/test/WorkspaceFoldersSpec.hs b/test/WorkspaceFoldersSpec.hs
index 747904bf1..9f176d6ef 100644
--- a/test/WorkspaceFoldersSpec.hs
+++ b/test/WorkspaceFoldersSpec.hs
@@ -32,7 +32,7 @@ spec = describe "workspace folders" $
             in handleMessage initCb tvarCtx clStr jsonStr
 
     let starterWorkspaces = List [wf0]
-        initParams = InitializeParams 
+        initParams = InitializeParams
           Nothing Nothing (Just (Uri "/foo")) Nothing fullCaps Nothing (Just starterWorkspaces)
         initMsg :: InitializeRequest
         initMsg = RequestMessage "2.0" (IdInt 0) Initialize initParams