diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Revision history for taskwarrior
 
+## 0.3.1.0
+
+* Add support with the JSON Format of taskwarrior 2.6.
+
 ## 0.3.0.0
 
 * Only export `id` and `urgency` when non default.
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -1,8 +1,8 @@
 # taskwarrior
 
-[![Hackage](https://img.shields.io/hackage/v/taskwarrior.svg)](https://hackage.haskell.org/package/taskwarrior)
-[![Build Status](https://img.shields.io/endpoint.svg?url=https%3A%2F%2Factions-badge.atrox.dev%2Fmaralorn%2Fhaskell-taskwarrior%2Fbadge%3Fref%3Dmaster)](https://actions-badge.atrox.dev/maralorn/haskell-taskwarrior/goto?ref=master)
 [![Hackage Deps](https://img.shields.io/hackage-deps/v/taskwarrior.svg)](http://packdeps.haskellers.com/reverse/taskwarrior)
+[![CI](https://github.com/maralorn/haskell-taskwarrior/actions/workflows/haskell.yml/badge.svg)](https://github.com/maralorn/haskell-taskwarrior/actions)
+[![Packaging status](https://repology.org/badge/vertical-allrepos/haskell:taskwarrior.svg?columns=3&header=)](https://repology.org/project/haskell:taskwarrior/versions)
 
 ## About
 
diff --git a/src/Taskwarrior/Annotation.hs b/src/Taskwarrior/Annotation.hs
--- a/src/Taskwarrior/Annotation.hs
+++ b/src/Taskwarrior/Annotation.hs
@@ -1,26 +1,26 @@
 -- | Provides the 'Annotation' type with 'Data.Aeson.ToJSON' and 'Data.Aeson.FromJSON' instances.
-module Taskwarrior.Annotation
-  ( Annotation(..)
-  )
-where
+module Taskwarrior.Annotation (
+  Annotation (..),
+) where
 
-import qualified Taskwarrior.Time              as Time
-import           Data.Time                      ( UTCTime )
-import           Data.Text                      ( Text )
-import           Data.Aeson                     ( (.:)
-                                                , (.=)
-                                                )
-import qualified Data.Aeson                    as Aeson
+import Data.Aeson (
+  (.:),
+  (.=),
+ )
+import qualified Data.Aeson as Aeson
+import Data.Text (Text)
+import Data.Time (UTCTime)
+import qualified Taskwarrior.Time as Time
 
 -- | A taskwarrior 'Taskwarrior.Task.Task' can have multiple annotations. They contain a timestamp 'entry' and a 'description'.
-data Annotation = Annotation { entry :: UTCTime, description :: Text } deriving (Eq, Show, Read, Ord)
+data Annotation = Annotation {entry :: UTCTime, description :: Text} deriving (Eq, Show, Read, Ord)
 
 instance Aeson.FromJSON Annotation where
   parseJSON = Aeson.withObject "Annotation" $ \o -> do
     description <- o .: "description"
-    entry       <- o .: "entry" >>= Time.parse
-    pure Annotation { .. }
+    entry <- o .: "entry" >>= Time.parse
+    pure Annotation{..}
 
 instance Aeson.ToJSON Annotation where
-  toJSON Annotation {..} =
+  toJSON Annotation{..} =
     Aeson.object ["description" .= description, "entry" .= Time.toValue entry]
diff --git a/src/Taskwarrior/IO.hs b/src/Taskwarrior/IO.hs
--- a/src/Taskwarrior/IO.hs
+++ b/src/Taskwarrior/IO.hs
@@ -1,106 +1,117 @@
--- | This modules contains IO actions to interact with the taskwarrior application.
--- The taskwarrior documentation very explicitly disallows accessing the files by itself.
--- So all functions here work via calling the @task@ binary which needs to be in the PATH.
-module Taskwarrior.IO
-  ( getTasks
-  , saveTasks
-  , createTask
-  , getUUIDs
-  , onAdd
-  , onAddPure
-  , onModify
-  , onModifyPure
-  )
-where
+{- | This modules contains IO actions to interact with the taskwarrior application.
+ The taskwarrior documentation very explicitly disallows accessing the files by itself.
+ So all functions here work via calling the @task@ binary which needs to be in the PATH.
+-}
+module Taskwarrior.IO (
+  getTasks,
+  saveTasks,
+  createTask,
+  getUUIDs,
+  onAdd,
+  onAddPure,
+  onModify,
+  onModifyPure,
+) where
 
-import           Taskwarrior.Task               ( Task
-                                                , makeTask
-                                                )
-import           Data.Text                      ( Text )
-import qualified Data.Text                     as Text
-import qualified Data.ByteString               as BS
-import qualified Data.ByteString.Lazy          as LBS
-                                         hiding ( putStrLn )
-import qualified Data.ByteString.Lazy.Char8    as LBS
-import qualified Data.Aeson                    as Aeson
-import           System.Process                 ( withCreateProcess
-                                                , CreateProcess(..)
-                                                , proc
-                                                , StdStream(..)
-                                                , waitForProcess
-                                                )
-import           System.IO                      ( hClose )
-import           System.Exit                    ( ExitCode(..) )
-import           Control.Monad                  ( when )
-import           System.Random                  ( getStdRandom
-                                                , random
-                                                )
-import           Data.Time                      ( getCurrentTime )
-import           Data.UUID                      ( UUID )
-import qualified Data.UUID                     as UUID
+import Control.Monad (when)
+import qualified Data.Aeson as Aeson
+import qualified Data.ByteString as BS
+import qualified Data.ByteString.Lazy as LBS hiding (
+  putStrLn,
+ )
+import qualified Data.ByteString.Lazy.Char8 as LBS
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Data.Time (getCurrentTime)
+import Data.UUID (UUID)
+import qualified Data.UUID as UUID
+import System.Exit (ExitCode (..))
+import System.IO (hClose)
+import System.Process (
+  CreateProcess (..),
+  StdStream (..),
+  proc,
+  waitForProcess,
+  withCreateProcess,
+ )
+import System.Random (
+  getStdRandom,
+  random,
+ )
+import Taskwarrior.Task (
+  Task,
+  makeTask,
+ )
 
 -- | Uses @task export@ with a given filter like @["description:Milk", "+PENDING"]@.
 getTasks :: [Text] -> IO [Task]
 getTasks args =
   withCreateProcess
-      ((proc "task" (fmap Text.unpack . (++ ["export"]) $ args))
+    ( (proc "task" (fmap Text.unpack . (++ ["export"]) $ args))
         { std_out = CreatePipe
         }
-      )
+    )
     $ \_ stdoutMay _ _ -> do
-        stdout <- maybe
+      stdout <-
+        maybe
           (fail "Couldn‘t create stdout handle for `task export`")
           pure
           stdoutMay
-        input <- LBS.hGetContents stdout
-        either fail return . Aeson.eitherDecode $ input
+      input <- LBS.hGetContents stdout
+      either fail return . Aeson.eitherDecode $ input
 
 -- | Gives all uuids matching the given filter (e.g. @["description:Milk", "+PENDING"]@). This calls the @task@ binary.
 getUUIDs :: [Text] -> IO [UUID]
 getUUIDs args =
   withCreateProcess
-      ((proc "task" (fmap Text.unpack . (++ ["_uuid"]) $ args)) { std_out = CreatePipe
-                                                                }
-      )
+    ( (proc "task" (fmap Text.unpack . (++ ["_uuid"]) $ args))
+        { std_out = CreatePipe
+        }
+    )
     $ \_ stdoutMay _ _ -> do
-        stdout <- maybe
+      stdout <-
+        maybe
           (fail "Couldn‘t create stdout handle for `task _uuid`")
           pure
           stdoutMay
-        input <- LBS.hGetContents stdout
-        maybe (fail "Couldn't parse UUIDs") return
-          . traverse UUID.fromLazyASCIIBytes
-          . LBS.lines
-          $ input
+      input <- LBS.hGetContents stdout
+      maybe (fail "Couldn't parse UUIDs") return
+        . traverse UUID.fromLazyASCIIBytes
+        . LBS.lines
+        $ input
 
 -- | Uses @task import@ to save the given tasks.
 saveTasks :: [Task] -> IO ()
 saveTasks tasks =
-  withCreateProcess ((proc "task" ["import"]) { std_in = CreatePipe })
-    $ \stdinMay _ _ process -> do
-        stdin <- maybe (fail "Couldn‘t create stdin handle for `task import`")
-                       pure
-                       stdinMay
-        LBS.hPut stdin . Aeson.encode $ tasks
-        hClose stdin
-        exitCode <- waitForProcess process
-        when (exitCode /= ExitSuccess) $ fail . show $ exitCode
+  withCreateProcess ((proc "task" ["import"]){std_in = CreatePipe}) $
+    \stdinMay _ _ process -> do
+      stdin <-
+        maybe
+          (fail "Couldn‘t create stdin handle for `task import`")
+          pure
+          stdinMay
+      LBS.hPut stdin . Aeson.encode $ tasks
+      hClose stdin
+      exitCode <- waitForProcess process
+      when (exitCode /= ExitSuccess) $ fail . show $ exitCode
 
--- | This will create a @'Task'@. I runs in @'IO'@ to create a @'UUID'@ and get the current time. This will not save the @'Task'@ to taskwarrior.
--- If you want to create a task with certain fields and save it you could do that like this:
---
--- @
--- newTask <- 'createTask' "Buy Milk"
--- 'saveTasks' [newTask { 'Taskwarrior.Task.tags' = ["groceries"] }]
--- @
+{- | This will create a @'Task'@. I runs in @'IO'@ to create a @'UUID'@ and get the current time. This will not save the @'Task'@ to taskwarrior.
+ If you want to create a task with certain fields and save it you could do that like this:
+
+ @
+ newTask <- 'createTask' "Buy Milk"
+ 'saveTasks' [newTask { 'Taskwarrior.Task.tags' = ["groceries"] }]
+ @
+-}
 createTask :: Text -> IO Task
 createTask description = do
-  uuid  <- getStdRandom random
+  uuid <- getStdRandom random
   entry <- getCurrentTime
   pure $ makeTask uuid entry description
 
--- | Takes a function @f originalTask modifiedTask = taskToSave@.
--- The resulting IO action can be run as the `main :: IO ()` of a taskwarrior on-modify hook.
+{- | Takes a function @f originalTask modifiedTask = taskToSave@.
+ The resulting IO action can be run as the `main :: IO ()` of a taskwarrior on-modify hook.
+-}
 onModifyPure :: (Task -> Task -> Task) -> IO ()
 onModifyPure f = onModify (\x y -> pure (f x y))
 
@@ -124,5 +135,7 @@
 
 -- | Like onAddPure with side effects.
 onAdd :: (Task -> IO Task) -> IO ()
-onAdd f = LBS.putStrLn . Aeson.encode =<< f =<< readTaskLine
-  "OnAdd hook couldn‘t parse task."
+onAdd f =
+  LBS.putStrLn . Aeson.encode =<< f
+    =<< readTaskLine
+      "OnAdd hook couldn‘t parse task."
diff --git a/src/Taskwarrior/Mask.hs b/src/Taskwarrior/Mask.hs
--- a/src/Taskwarrior/Mask.hs
+++ b/src/Taskwarrior/Mask.hs
@@ -1,13 +1,12 @@
 -- | The Mask module models the state a recurring parent saves about its child tasks.
-module Taskwarrior.Mask
-  ( Mask(..)
-  , MaskState
-  )
-where
+module Taskwarrior.Mask (
+  Mask (..),
+  MaskState,
+) where
 
-import qualified Data.Text                     as Text
-import qualified Data.Aeson                    as Aeson
-import qualified Data.Aeson.Types              as Aeson.Types
+import qualified Data.Aeson as Aeson
+import qualified Data.Aeson.Types as Aeson.Types
+import qualified Data.Text as Text
 
 -- | Represents the state of a child in a 'Status.Recurring' 'Task.Task'.
 data MaskState = Pending | Completed | Deleted | Waiting deriving (Eq, Show, Enum, Read, Ord, Bounded)
@@ -17,10 +16,10 @@
 
 toChar :: MaskState -> Char
 toChar = \case
-  Pending   -> '-'
+  Pending -> '-'
   Completed -> '+'
-  Deleted   -> 'X'
-  Waiting   -> 'W'
+  Deleted -> 'X'
+  Waiting -> 'W'
 
 instance Aeson.FromJSON Mask where
   parseJSON =
@@ -28,10 +27,10 @@
 
 parseChar :: Char -> Aeson.Types.Parser MaskState
 parseChar = \case
-  '-'  -> pure Pending
-  '+'  -> pure Completed
-  'X'  -> pure Deleted
-  'W'  -> pure Waiting
+  '-' -> pure Pending
+  '+' -> pure Completed
+  'X' -> pure Deleted
+  'W' -> pure Waiting
   char -> fail $ "Not a Mask Char: '" ++ [char] ++ "'"
 
 instance Aeson.ToJSON Mask where
diff --git a/src/Taskwarrior/Priority.hs b/src/Taskwarrior/Priority.hs
--- a/src/Taskwarrior/Priority.hs
+++ b/src/Taskwarrior/Priority.hs
@@ -1,23 +1,21 @@
 -- | This module provides the type for the 'Priority' of a task.
-module Taskwarrior.Priority
-  ( parseMay
-  , Priority(..)
-  )
-where
-
-import qualified Data.Aeson                    as Aeson
-import           Data.Aeson.Types               ( Parser )
+module Taskwarrior.Priority (
+  parseMay,
+  Priority (..),
+) where
 
+import qualified Data.Aeson as Aeson
+import Data.Aeson.Types (Parser)
 
 -- | A 'Taskwarrior.Task.Task' can have the priorities 'High', 'Medium', 'Low' or none, which is modeled via a 'Maybe' 'Priority'.
 data Priority = High | Medium | Low
-        deriving (Eq, Show, Read, Enum, Ord, Bounded)
+  deriving (Eq, Show, Read, Enum, Ord, Bounded)
 
 instance Aeson.ToJSON Priority where
   toJSON = \case
-    High   -> "H"
+    High -> "H"
     Medium -> "M"
-    Low    -> "L"
+    Low -> "L"
 
 -- | Parses a JSON string to a 'Maybe' 'Priority', fails on anything else.
 parseMay :: Aeson.Value -> Parser (Maybe Priority)
@@ -25,16 +23,17 @@
   "H" -> pure $ Just High
   "M" -> pure $ Just Medium
   "L" -> pure $ Just Low
-  ""  -> pure Nothing
+  "" -> pure Nothing
   s ->
-    fail
-      $  "parsing Priority failed, unexpected "
-      ++ show s
-      ++ " (expected \"H\", \"M\", \"L\", or \"\")"
+    fail $
+      "parsing Priority failed, unexpected "
+        ++ show s
+        ++ " (expected \"H\", \"M\", \"L\", or \"\")"
 
 instance Aeson.FromJSON Priority where
-  parseJSON val = parseMay val >>= \case
-    Nothing ->
-      fail
-        "parsing Priority failed, unexpected null (expected \"H\", \"M\", or \"L\")"
-    Just p -> pure p
+  parseJSON val =
+    parseMay val >>= \case
+      Nothing ->
+        fail
+          "parsing Priority failed, unexpected null (expected \"H\", \"M\", or \"L\")"
+      Just p -> pure p
diff --git a/src/Taskwarrior/RecurringChild.hs b/src/Taskwarrior/RecurringChild.hs
--- a/src/Taskwarrior/RecurringChild.hs
+++ b/src/Taskwarrior/RecurringChild.hs
@@ -1,36 +1,39 @@
--- | This Module provides the RecurringChild type with
--- FromJSON and ToJSON instances.
-module Taskwarrior.RecurringChild
-  ( RecurringChild(..)
-  , parseFromObjectMay
-  , toPairs
-  )
-where
+{- | This Module provides the RecurringChild type with
+ FromJSON and ToJSON instances.
+-}
+module Taskwarrior.RecurringChild (
+  RecurringChild (..),
+  parseFromObjectMay,
+  toPairs,
+) where
 
-import           Control.Applicative            ( optional )
-import           Data.Aeson                     ( Object
-                                                , (.:)
-                                                , (.=)
-                                                , ToJSON
-                                                , FromJSON
-                                                , pairs
-                                                , object
-                                                , withObject
-                                                )
-import qualified Data.Aeson                    as Aeson
-import           Data.Aeson.Types               ( Parser
-                                                , Pair
-                                                )
-import           Data.Text                      ( Text )
-import           Data.UUID                      ( UUID )
+import Control.Applicative (optional)
+import Data.Aeson (
+  FromJSON,
+  Object,
+  ToJSON,
+  object,
+  pairs,
+  withObject,
+  (.:),
+  (.=),
+ )
+import qualified Data.Aeson as Aeson
+import Data.Aeson.Types (
+  Pair,
+  Parser,
+ )
+import Data.Text (Text)
+import Data.UUID (UUID)
 
--- | The 'RecurringChild' type saves information about how a 'Taskwarrior.Task.Task'
--- is child of another 'Taskwarrior.Task.Task' wich is recurring.
-data RecurringChild =
-  RecurringChild {
-  recur :: Text,
-  imask :: Integer,
-  parent :: UUID }
+{- | The 'RecurringChild' type saves information about how a 'Taskwarrior.Task.Task'
+ is child of another 'Taskwarrior.Task.Task' wich is recurring.
+-}
+data RecurringChild = RecurringChild
+  { recur :: Text
+  , imask :: Integer
+  , parent :: UUID
+  }
   deriving (Eq, Show, Read, Ord)
 
 -- | Gathers all fields for a 'RecurringChild' status.
@@ -43,12 +46,12 @@
 
 -- | Can be used to serialize 'RecurringChild' to JSON.
 toPairs :: RecurringChild -> [Pair]
-toPairs RecurringChild {..} =
+toPairs RecurringChild{..} =
   ["recur" .= recur, "imask" .= imask, "parent" .= parent]
 
 instance FromJSON RecurringChild where
   parseJSON = withObject "RecurringChild" parseFromObject
 
 instance ToJSON RecurringChild where
-  toJSON     = object . toPairs
+  toJSON = object . toPairs
   toEncoding = pairs . mconcat . map (uncurry (.=)) . toPairs
diff --git a/src/Taskwarrior/Status.hs b/src/Taskwarrior/Status.hs
--- a/src/Taskwarrior/Status.hs
+++ b/src/Taskwarrior/Status.hs
@@ -1,60 +1,64 @@
 -- | This module deals with information of a task which is dependent on the status.
-module Taskwarrior.Status
-  ( Status(..)
-  , parseFromObject
-  , toPairs
-  )
-where
+module Taskwarrior.Status (
+  Status (..),
+  parseFromObject,
+  toPairs,
+) where
 
-import           Taskwarrior.Mask               ( Mask )
-import qualified Taskwarrior.Time              as Time
-import           Data.Aeson                     ( Object
-                                                , (.:)
-                                                , (.=)
-                                                , ToJSON
-                                                , FromJSON
-                                                , pairs
-                                                , object
-                                                , withObject
-                                                )
-import qualified Data.Aeson                    as Aeson
-import           Data.Text                      ( Text )
-import           Data.Time                      ( UTCTime )
-import           Data.Aeson.Types               ( Parser
-                                                , typeMismatch
-                                                , Pair
-                                                )
+import Data.Aeson (
+  FromJSON,
+  Object,
+  ToJSON,
+  object,
+  pairs,
+  withObject,
+  (.:),
+  (.=),
+ )
+import qualified Data.Aeson as Aeson
+import Data.Aeson.Types (
+  Pair,
+  Parser,
+  typeMismatch,
+ )
+import Data.Text (Text)
+import Data.Time (UTCTime)
+import Taskwarrior.Mask (Mask)
+import qualified Taskwarrior.Time as Time
 
--- | A task can be pending, deleted, completed, waiting or recurring.
--- It is recommended to access the fields only by pattern matching since the getters are partial.
-data Status =
-  Pending |
-  Deleted {  end :: UTCTime } |
-  Completed {  end :: UTCTime } |
-  Waiting { wait :: UTCTime } |
-  Recurring {
-    recur :: Text,
-    mask :: Mask}
+{- | A task can be pending, deleted, completed, waiting or recurring.
+ It is recommended to access the fields only by pattern matching since the getters are partial.
+-}
+data Status
+  = Pending
+  | Deleted {end :: UTCTime}
+  | Completed {end :: UTCTime}
+  | Waiting {wait :: UTCTime}
+  | Recurring
+      { recur :: Text
+      , mask :: Mask
+      }
   deriving (Eq, Show, Read, Ord)
 
 -- | Takes all information that is dependent on the status from a JSON object.
 parseFromObject :: Object -> Parser Status
-parseFromObject o = (o .: "status") >>= \case
-  "pending"   -> pure Pending
-  "deleted"   -> Deleted <$> (o .: "end" >>= Time.parse)
-  "completed" -> Completed <$> (o .: "end" >>= Time.parse)
-  "waiting"   -> Waiting <$> (o .: "wait" >>= Time.parse)
-  "recurring" -> Recurring <$> o .: "recur" <*> o .: "mask"
-  str         -> typeMismatch "status" (Aeson.String str)
+parseFromObject o =
+  (o .: "status") >>= \case
+    "pending" -> pure Pending
+    "deleted" -> Deleted <$> (o .: "end" >>= Time.parse)
+    "completed" -> Completed <$> (o .: "end" >>= Time.parse)
+    "waiting" -> Waiting <$> (o .: "wait" >>= Time.parse)
+    "recurring" -> Recurring <$> o .: "recur" <*> o .: "mask"
+    str -> typeMismatch "status" (Aeson.String str)
 
 -- | A list of Pairs can be used to construct a JSON object later. The result of 'toPairs' is supposed to be combined with the rest of the fields of a task.
 toPairs :: Status -> [Pair]
 toPairs = \case
-  Pending        -> [statusLabel "pending"]
-  Deleted {..}   -> [statusLabel "deleted", "end" .= Time.toValue end]
-  Completed {..} -> [statusLabel "completed", "end" .= Time.toValue end]
-  Waiting {..}   -> [statusLabel "waiting", "wait" .= Time.toValue wait]
-  Recurring {..} -> [statusLabel "recurring", "recur" .= recur, "mask" .= mask]
+  Pending -> [statusLabel "pending"]
+  Deleted{..} -> [statusLabel "deleted", "end" .= Time.toValue end]
+  Completed{..} -> [statusLabel "completed", "end" .= Time.toValue end]
+  Waiting{..} -> [statusLabel "waiting", "wait" .= Time.toValue wait]
+  Recurring{..} -> [statusLabel "recurring", "recur" .= recur, "mask" .= mask]
  where
   statusLabel :: Text -> Pair
   statusLabel = ("status" .=)
@@ -63,5 +67,5 @@
   parseJSON = withObject "Status" parseFromObject
 
 instance ToJSON Status where
-  toJSON     = object . toPairs
+  toJSON = object . toPairs
   toEncoding = pairs . mconcat . map (uncurry (.=)) . toPairs
diff --git a/src/Taskwarrior/Task.hs b/src/Taskwarrior/Task.hs
--- a/src/Taskwarrior/Task.hs
+++ b/src/Taskwarrior/Task.hs
@@ -1,93 +1,98 @@
--- | This Module exports the main datatype of this library: Task.
--- It is provided with FromJSON and ToJSON instances.
---
-module Taskwarrior.Task
-  ( Task(..)
-  , Tag
-  , makeTask
-  -- | == Adherence to specification
-  -- This library uses the [taskwarrior specification for the JSON serialisation format](https://taskwarrior.org/docs/design/task.html).
-  -- But it deviates in a small number of ways to be more pragmatic.
-  --
-  -- * 'Task' has the fields 'id' and 'urgency' although they are technically UDAs.
-  -- * There are two invalid states which are not prevented via the Haskell type system by the chosen modeling:
-  --
-  --   1. A 'Task' with a 'Just' value for 'recurringChild' should not have the 'Status' 'Taskwarrior.Status.Recurring'.
-  --   2. The 'due' field needs to be a 'Just' value on a 'Task' with 'Status' 'Taskwarrior.Status.Recurring'.
-  )
-where
+{- | This Module exports the main datatype of this library: Task.
+ It is provided with FromJSON and ToJSON instances.
+-}
+module Taskwarrior.Task (
+  Task (..),
+  Tag,
+  makeTask,
+  {-
+   | == Adherence to specification
+   This library uses the [taskwarrior specification for the JSON serialisation format](https://taskwarrior.org/docs/design/task.html).
+   But it deviates in a small number of ways to be more pragmatic.
 
-import           Prelude                 hiding ( id )
+   * 'Task' has the fields 'id' and 'urgency' although they are technically UDAs.
+   * There are two invalid states which are not prevented via the Haskell type system by the chosen modeling:
 
-import qualified Data.Text                     as Text
-import           Data.Text                      ( Text )
-import           Data.Time                      ( UTCTime )
-import qualified Data.UUID                     as UUID
-import           Data.UUID                      ( UUID )
-import qualified Data.Aeson                    as Aeson
-import qualified Data.Aeson.Types              as Aeson.Types
-import           Data.Aeson                     ( withObject
-                                                , withText
-                                                , FromJSON
-                                                , ToJSON
-                                                , parseJSON
-                                                , (.:)
-                                                , (.=)
-                                                , (.:?)
-                                                , Value
-                                                )
-import qualified Data.Semigroup                as Semigroup
-import           Data.Maybe                     ( fromMaybe )
-import qualified Data.Maybe                    as Maybe
-import           Control.Monad                  ( join )
-import qualified Data.Foldable                 as Foldable
-import           Taskwarrior.Status             ( Status )
-import qualified Taskwarrior.Status            as Status
-import           Taskwarrior.RecurringChild     ( RecurringChild )
-import qualified Taskwarrior.RecurringChild    as RecurringChild
-import           Taskwarrior.Priority           ( Priority )
-import qualified Taskwarrior.Priority          as Priority
-import           Taskwarrior.UDA                ( UDA )
-import           Taskwarrior.Annotation         ( Annotation )
-import qualified Taskwarrior.Time              as Time
-import qualified Data.HashMap.Strict           as HashMap
-import           Data.Set                       ( Set )
-import qualified Data.Set                      as Set
-import           Foreign.Marshal.Utils          ( fromBool )
+     1. A 'Task' with a 'Just' value for 'recurringChild' should not have the 'Status' 'Taskwarrior.Status.Recurring'.
+     2. The 'due' field needs to be a 'Just' value on a 'Task' with 'Status' 'Taskwarrior.Status.Recurring'.
+  -}
+) where
 
--- | A 'Task' represents a task from taskwarrior.
--- The specification demands, that the existence of some fields is dependent on the status of the task.
--- Those fields are therefore bundled in 'Status' as a sum-type.
---
--- All fields in an imported task which are not part of the specification will be put in the 'UDA' (user defined attributes) 'Data.HashMap.Strict.HashMap'.
---
--- Since the json can have multiple semantically equivalent representations of a task first serializing and then deserializing is not identity.
--- But deserializing and then serializing should be. (Thus making serializing and deserializing idempotent.)
-data Task = Task {
-        status         :: Status,
-        recurringChild :: Maybe RecurringChild,
-        uuid           :: UUID,
-        id             :: Maybe Integer,
-        entry          :: UTCTime,
-        description    :: Text,
-        start          :: Maybe UTCTime,
-        modified       :: Maybe UTCTime,
-        due            :: Maybe UTCTime,
-        until          :: Maybe UTCTime,
-        annotations    :: Set Annotation,
-        scheduled      :: Maybe UTCTime,
-        project        :: Maybe Text,
-        priority       :: Maybe Priority,
-        depends        :: Set UUID,
-        tags           :: Set Tag,
-        urgency        :: Double,
-        uda            :: UDA
-} deriving (Eq, Show, Read)
+import Prelude hiding (id)
 
+import Control.Monad (join)
+import Data.Aeson (
+  FromJSON,
+  ToJSON,
+  Value,
+  parseJSON,
+  withObject,
+  withText,
+  (.:),
+  (.:?),
+  (.=), withArray
+ )
+import qualified Data.Aeson as Aeson
+import qualified Data.Aeson.Types as Aeson.Types
+import qualified Data.Foldable as Foldable
+import qualified Data.HashMap.Strict as HashMap
+import Data.Maybe (fromMaybe)
+import qualified Data.Maybe as Maybe
+import qualified Data.Semigroup as Semigroup
+import Data.Set (Set)
+import qualified Data.Set as Set
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Data.Time (UTCTime)
+import Data.UUID (UUID)
+import qualified Data.UUID as UUID
+import Foreign.Marshal.Utils (fromBool)
+import Taskwarrior.Annotation (Annotation)
+import Taskwarrior.Priority (Priority)
+import qualified Taskwarrior.Priority as Priority
+import Taskwarrior.RecurringChild (RecurringChild)
+import qualified Taskwarrior.RecurringChild as RecurringChild
+import Taskwarrior.Status (Status)
+import qualified Taskwarrior.Status as Status
+import qualified Taskwarrior.Time as Time
+import Taskwarrior.UDA (UDA)
+import Data.Foldable (toList)
+import Control.Applicative ((<|>))
+
+{- | A 'Task' represents a task from taskwarrior.
+ The specification demands, that the existence of some fields is dependent on the status of the task.
+ Those fields are therefore bundled in 'Status' as a sum-type.
+
+ All fields in an imported task which are not part of the specification will be put in the 'UDA' (user defined attributes) 'Data.HashMap.Strict.HashMap'.
+
+ Since the json can have multiple semantically equivalent representations of a task first serializing and then deserializing is not identity.
+ But deserializing and then serializing should be. (Thus making serializing and deserializing idempotent.)
+-}
+data Task = Task
+  { status :: Status
+  , recurringChild :: Maybe RecurringChild
+  , uuid :: UUID
+  , id :: Maybe Integer
+  , entry :: UTCTime
+  , description :: Text
+  , start :: Maybe UTCTime
+  , modified :: Maybe UTCTime
+  , due :: Maybe UTCTime
+  , until :: Maybe UTCTime
+  , annotations :: Set Annotation
+  , scheduled :: Maybe UTCTime
+  , project :: Maybe Text
+  , priority :: Maybe Priority
+  , depends :: Set UUID
+  , tags :: Set Tag
+  , urgency :: Double
+  , uda :: UDA
+  }
+  deriving (Eq, Show, Read)
+
 -- | A Tag can be basically any string. But beware: Special symbols work but might clash with @task@ cli syntax. As an example you can use a space in a @'Tag'@. But then you cannot use @task +my tag@ on the command line.
 type Tag = Text
 
-
 reservedKeys :: [Text]
 reservedKeys =
   [ "status"
@@ -118,102 +123,108 @@
   parseJSON = withObject "Task" $ \object -> do
     let parseTimeFromFieldMay = parseFromFieldWithMay Time.parse object
         uda = HashMap.filterWithKey (\k _ -> k `notElem` reservedKeys) object
-    status         <- Status.parseFromObject object
+    status <- Status.parseFromObject object
     recurringChild <- RecurringChild.parseFromObjectMay object
-    uuid           <- object .: "uuid"
-    idRaw          <- object .:? "id"
+    uuid <- object .: "uuid"
+    idRaw <- object .:? "id"
     let id = if idRaw == Just 0 then Nothing else idRaw
-    entry       <- object .: "entry" >>= Time.parse
+    entry <- object .: "entry" >>= Time.parse
     description <- object .: "description"
-    start       <- parseTimeFromFieldMay "start"
-    modified    <- parseTimeFromFieldMay "modified"
-    due         <- parseTimeFromFieldMay "due"
-    until_      <- parseTimeFromFieldMay "until"
-    scheduled   <- parseTimeFromFieldMay "scheduled"
+    start <- parseTimeFromFieldMay "start"
+    modified <- parseTimeFromFieldMay "modified"
+    due <- parseTimeFromFieldMay "due"
+    until_ <- parseTimeFromFieldMay "until"
+    scheduled <- parseTimeFromFieldMay "scheduled"
     annotations <- Foldable.fold <$> object .:? "annotations"
-    project     <- object .:? "project"
-    priority    <- join
-      <$> parseFromFieldWithMay Priority.parseMay object "priority"
-    depends <- maybe (pure mempty)
-                     parseUuidList
-                     (HashMap.lookup "depends" object)
-    tags    <- Foldable.fold <$> object .:? "tags"
+    project <- object .:? "project"
+    priority <-
+      join
+        <$> parseFromFieldWithMay Priority.parseMay object "priority"
+    depends <-
+      maybe
+        (pure mempty)
+        parseUuidList
+        (HashMap.lookup "depends" object)
+    tags <- Foldable.fold <$> object .:? "tags"
     urgency <- fromMaybe 0 <$> object .:? "urgency"
-    pure Task { until = until_, .. }
+    pure Task{until = until_, ..}
 
-parseFromFieldWithMay
-  :: (Value -> Aeson.Types.Parser a)
-  -> Aeson.Object
-  -> Text
-  -> Aeson.Types.Parser (Maybe a)
+parseFromFieldWithMay ::
+  (Value -> Aeson.Types.Parser a) ->
+  Aeson.Object ->
+  Text ->
+  Aeson.Types.Parser (Maybe a)
 parseFromFieldWithMay parser object name =
   traverse parser (HashMap.lookup name object)
 
 parseUuidList :: Aeson.Value -> Aeson.Types.Parser (Set UUID)
-parseUuidList =
-  withText "Text"
-    $ fmap Set.fromList
-    . mapM (parseJSON . Aeson.String)
-    . Text.splitOn ","
+parseUuidList val =
+  (withArray "Array of uuid strings" $ fmap Set.fromList . mapM parseJSON . toList) val <|>
+  (withText "Comma separated list of uuids" $
+    fmap Set.fromList
+      . mapM (parseJSON . Aeson.String)
+      . Text.splitOn ",") val
 
 instance ToJSON Task where
-  toJSON Task { until = until_, ..} =
-    Aeson.object
-      $  Status.toPairs status
-      <> [ "uuid" .= uuid
-         , "entry" .= Time.toValue entry
-         , "description" .= description
-         ]
-      <> [ "urgency" .= urgency | urgency /= 0 ]
-      <> maybe [] RecurringChild.toPairs recurringChild
-      <> ifNotNullSet annotations ("annotations" .=)
-      <> Maybe.mapMaybe
-           (\(name, value) -> (name .=) . Time.toValue <$> value)
-           [ ("start"    , start)
-           , ("modified" , modified)
-           , ("due"      , due)
-           , ("scheduled", scheduled)
-           , ("until"    , until_)
-           ]
-      <> Maybe.catMaybes
-           [ ("id" .=) <$> id
-           , ("project" .=) <$> project
-           , ("priority" .=) <$> priority
+  toJSON Task{until = until_, ..} =
+    Aeson.object $
+      Status.toPairs status
+        <> [ "uuid" .= uuid
+           , "entry" .= Time.toValue entry
+           , "description" .= description
            ]
-      <> ifNotNullSet
-           depends
-           ( ("depends" .=)
-           . Text.intercalate ","
-           . fmap UUID.toText
-           . Set.toList
-           )
-      <> ifNotNullSet tags ("tags" .=)
-      <> HashMap.toList uda
+        <> ["urgency" .= urgency | urgency /= 0]
+        <> maybe [] RecurringChild.toPairs recurringChild
+        <> ifNotNullSet annotations ("annotations" .=)
+        <> Maybe.mapMaybe
+          (\(name, value) -> (name .=) . Time.toValue <$> value)
+          [ ("start", start)
+          , ("modified", modified)
+          , ("due", due)
+          , ("scheduled", scheduled)
+          , ("until", until_)
+          ]
+        <> Maybe.catMaybes
+          [ ("id" .=) <$> id
+          , ("project" .=) <$> project
+          , ("priority" .=) <$> priority
+          ]
+        <> ifNotNullSet
+          depends
+          ( ("depends" .=)
+              . Text.intercalate ","
+              . fmap UUID.toText
+              . Set.toList
+          )
+        <> ifNotNullSet tags ("tags" .=)
+        <> HashMap.toList uda
 
 ifNotNullSet :: (Ord b) => Set b -> (Set b -> a) -> [a]
 ifNotNullSet set f =
-  (Semigroup.stimesMonoid . (fromBool :: Bool -> Integer) . not . Set.null $ set
-    )
+  ( Semigroup.stimesMonoid . (fromBool :: Bool -> Integer) . not . Set.null $ set
+  )
     [f set]
 
 -- | Makes a Task with the given mandatory fields uuid, entry time and description. See createTask for a non-pure version which needs less parameters.
 makeTask :: UUID -> UTCTime -> Text -> Task
-makeTask uuid entry description = Task { uuid
-                                       , description
-                                       , entry
-                                       , id             = Nothing
-                                       , modified       = Just entry
-                                       , status         = Status.Pending
-                                       , recurringChild = Nothing
-                                       , due            = Nothing
-                                       , priority       = Nothing
-                                       , project        = Nothing
-                                       , start          = Nothing
-                                       , scheduled      = Nothing
-                                       , until          = Nothing
-                                       , annotations    = mempty
-                                       , depends        = mempty
-                                       , tags           = mempty
-                                       , urgency        = 0
-                                       , uda            = HashMap.empty
-                                       }
+makeTask uuid entry description =
+  Task
+    { uuid
+    , description
+    , entry
+    , id = Nothing
+    , modified = Just entry
+    , status = Status.Pending
+    , recurringChild = Nothing
+    , due = Nothing
+    , priority = Nothing
+    , project = Nothing
+    , start = Nothing
+    , scheduled = Nothing
+    , until = Nothing
+    , annotations = mempty
+    , depends = mempty
+    , tags = mempty
+    , urgency = 0
+    , uda = HashMap.empty
+    }
diff --git a/src/Taskwarrior/Time.hs b/src/Taskwarrior/Time.hs
--- a/src/Taskwarrior/Time.hs
+++ b/src/Taskwarrior/Time.hs
@@ -1,34 +1,39 @@
 -- | This module provides no own time type for taskwarrior rather it only gives deserialisation and serialisation support.
-module Taskwarrior.Time
-  ( parse
-  , toValue
-  )
-where
-import           Data.Aeson                     ( withText )
-import qualified Data.Aeson                    as Aeson
-import           Data.Aeson.Types               ( Parser
-                                                , typeMismatch
-                                                )
-import           Data.Time                      ( UTCTime
-                                                , parseTimeM
-                                                , defaultTimeLocale
-                                                )
-import qualified Data.Time.Format              as Time.Format
-import qualified Data.Text                     as Text
+module Taskwarrior.Time (
+  parse,
+  toValue,
+) where
 
+import Data.Aeson (withText)
+import qualified Data.Aeson as Aeson
+import Data.Aeson.Types (
+  Parser,
+  typeMismatch,
+ )
+import qualified Data.Text as Text
+import Data.Time (
+  UTCTime,
+  defaultTimeLocale,
+  parseTimeM,
+ )
+import qualified Data.Time.Format as Time.Format
+
 -- | Converts a time to the taskwarrior time format.
 toValue :: UTCTime -> Aeson.Value
-toValue time = Aeson.String . Text.pack $ Time.Format.formatTime
-  defaultTimeLocale
-  "%Y%m%dT%H%M%SZ"
-  time
+toValue time =
+  Aeson.String . Text.pack $
+    Time.Format.formatTime
+      defaultTimeLocale
+      "%Y%m%dT%H%M%SZ"
+      time
 
 -- | Parses a JSON string from the taskwarrior time format.
 parse :: Aeson.Value -> Parser UTCTime
-parse value = withText
-  "Date"
-  ( maybe (typeMismatch "Date" value) pure
-  . parseTimeM False defaultTimeLocale "%Y%m%dT%H%M%SZ"
-  . Text.unpack
-  )
-  value
+parse value =
+  withText
+    "Date"
+    ( maybe (typeMismatch "Date" value) pure
+        . parseTimeM False defaultTimeLocale "%Y%m%dT%H%M%SZ"
+        . Text.unpack
+    )
+    value
diff --git a/src/Taskwarrior/UDA.hs b/src/Taskwarrior/UDA.hs
--- a/src/Taskwarrior/UDA.hs
+++ b/src/Taskwarrior/UDA.hs
@@ -1,12 +1,11 @@
 -- | User defined attributes are stored in a 'HashMap' from 'Text' to json 'Value's because we have no type information about them.
-module Taskwarrior.UDA
-  ( UDA
-  )
-where
+module Taskwarrior.UDA (
+  UDA,
+) where
 
-import           Data.Text                      ( Text )
-import           Data.HashMap.Strict            ( HashMap )
-import           Data.Aeson                     ( Value )
+import Data.Aeson (Value)
+import Data.HashMap.Strict (HashMap)
+import Data.Text (Text)
 
 -- | A field will in practice only be a number or a string.
 type UDA = HashMap Text Value
diff --git a/taskwarrior.cabal b/taskwarrior.cabal
--- a/taskwarrior.cabal
+++ b/taskwarrior.cabal
@@ -4,7 +4,7 @@
 -- PVP summary:     +-+------- breaking API changes
 --                  | | +----- non-breaking API additions
 --                  | | | +--- code changes with no API change
-version: 0.3.0.0
+version: 0.3.1.0
 synopsis:           Types and aeson instances for taskwarrior tasks
 description:
   Types and aeson instances for the https://taskwarrior.org task import/export feature
@@ -45,14 +45,14 @@
     StrictData
 
   build-depends:
-    , aeson                 ^>=1.4.2.0
-    , base                  >=4.11     && <4.15
-    , bytestring            ^>=0.10.8.2
-    , containers            >=0.5.0.0  && <0.7
+    , aeson                 >=1.4.2.0  && < 1.6
+    , base                  >=4.11     && < 4.16
+    , bytestring            >=0.10.8.2 && < 0.12
+    , containers            >=0.5.0.0  && < 0.7
     , process               ^>=1.6.5.0
-    , random                ^>=1.1
+    , random                >=1.1      && < 1.3
     , text                  ^>=1.2.3.0
-    , time                  >=1.8.0.2  && <1.11
+    , time                  >=1.8.0.2  && < 1.13
     , unordered-containers  ^>=0.2.9.0
     , uuid                  ^>=1.3.13
 
@@ -69,7 +69,7 @@
   build-depends:
     , aeson
     , base
-    , hspec                 ^>=2.7.1
+    , hspec                 >=2.7.1 && < 2.9
     , QuickCheck            >=2.13.2 && <2.15
     , quickcheck-instances  ^>=0.3.22
     , taskwarrior
diff --git a/test/TaskSpec.hs b/test/TaskSpec.hs
--- a/test/TaskSpec.hs
+++ b/test/TaskSpec.hs
@@ -1,28 +1,29 @@
 {-# LANGUAGE RecordWildCards #-}
-module TaskSpec
-  ( spec
-  )
-where
 
-import           Prelude                 hiding ( id )
-import           Control.Arrow                  ( second )
+module TaskSpec (
+  spec,
+) where
 
-import           Test.Hspec
-import           Test.QuickCheck
-import           Data.Aeson
-import           Taskwarrior.Task
-import           Taskwarrior.Mask
-import           Taskwarrior.Status
-import           Taskwarrior.RecurringChild
-import           Taskwarrior.Annotation
-import           Taskwarrior.Priority
-import           Data.Time
-import qualified Data.HashMap.Strict           as HashMap
-import           Test.QuickCheck.Instances.Text ( )
-import           Test.QuickCheck.Instances.UUID ( )
-import           Test.QuickCheck.Instances.UnorderedContainers
-                                                ( )
+import Control.Arrow (second)
+import Prelude hiding (id)
 
+import Data.Aeson
+import qualified Data.HashMap.Strict as HashMap
+import Data.Time
+import Taskwarrior.Annotation
+import Taskwarrior.Mask
+import Taskwarrior.Priority
+import Taskwarrior.RecurringChild
+import Taskwarrior.Status
+import Taskwarrior.Task
+import Test.Hspec
+import Test.QuickCheck
+import Test.QuickCheck.Instances.Text ()
+import Test.QuickCheck.Instances.UUID ()
+import Test.QuickCheck.Instances.UnorderedContainers (
+
+ )
+
 prop_taskDeEncode :: Task -> Property
 prop_taskDeEncode task = Just task === decode (encode task)
 
@@ -32,8 +33,8 @@
 spec :: Spec
 spec = do
   it "will be the same after read . show" $ property prop_taskReadShow
-  it "will be the same after encoding to JSON and decoding"
-    $ property prop_taskDeEncode
+  it "will be the same after encoding to JSON and decoding" $
+    property prop_taskDeEncode
 
 instance Arbitrary MaskState where
   arbitrary = arbitraryBoundedEnum
@@ -42,52 +43,53 @@
   arbitrary = Mask <$> (arbitrary :: Gen [MaskState])
 
 instance Arbitrary Status where
-  arbitrary = oneof
-    [ pure Pending
-    , Deleted <$> arbitrary
-    , Completed <$> arbitrary
-    , Waiting <$> arbitrary
-    , Recurring <$> arbitrary <*> arbitrary
-    ]
+  arbitrary =
+    oneof
+      [ pure Pending
+      , Deleted <$> arbitrary
+      , Completed <$> arbitrary
+      , Waiting <$> arbitrary
+      , Recurring <$> arbitrary <*> arbitrary
+      ]
 
 instance Arbitrary RecurringChild where
   arbitrary = RecurringChild <$> arbitrary <*> arbitrary <*> arbitrary
 
 instance Arbitrary UTCTime where
   arbitrary = do
-    day     <- ModifiedJulianDay <$> arbitrary
+    day <- ModifiedJulianDay <$> arbitrary
     dayTime <- secondsToDiffTime <$> choose (0, 86400)
     pure $ UTCTime day dayTime
 
 instance Arbitrary Annotation where
   arbitrary = do
-    entry       <- arbitrary
+    entry <- arbitrary
     description <- arbitrary
-    pure Annotation { .. }
+    pure Annotation{..}
 
 instance Arbitrary Priority where
   arbitrary = arbitraryBoundedEnum
 
 instance Arbitrary Task where
   arbitrary = do
-    status         <- arbitrary
+    status <- arbitrary
     recurringChild <- case status of
       Recurring{} -> pure Nothing -- A task cannot be both a parent and child recurrence
-      _           -> arbitrary
-    uuid        <- arbitrary
-    id          <- arbitrary `suchThat` maybe True (>= 1) -- IDs can't be negative, and 0 is used as "not present"
-    entry       <- arbitrary
+      _ -> arbitrary
+    uuid <- arbitrary
+    id <- arbitrary `suchThat` maybe True (>= 1) -- IDs can't be negative, and 0 is used as "not present"
+    entry <- arbitrary
     description <- arbitrary
-    start       <- arbitrary
-    modified    <- arbitrary
-    due         <- arbitrary
-    until_      <- arbitrary
+    start <- arbitrary
+    modified <- arbitrary
+    due <- arbitrary
+    until_ <- arbitrary
     annotations <- arbitrary
-    scheduled   <- arbitrary
-    project     <- arbitrary
-    priority    <- arbitrary
-    depends     <- arbitrary
-    tags        <- arbitrary
-    urgency     <- arbitrary
-    uda         <- HashMap.fromList . fmap (second String) <$> arbitrary
-    pure Task { until = until_, .. }
+    scheduled <- arbitrary
+    project <- arbitrary
+    priority <- arbitrary
+    depends <- arbitrary
+    tags <- arbitrary
+    urgency <- arbitrary
+    uda <- HashMap.fromList . fmap (second String) <$> arbitrary
+    pure Task{until = until_, ..}