diff --git a/src/Internal/Config/Text.elm b/src/Internal/Config/Text.elm
index 745b15b..1159868 100644
--- a/src/Internal/Config/Text.elm
+++ b/src/Internal/Config/Text.elm
@@ -1,8 +1,9 @@
 module Internal.Config.Text exposing
-    ( accessTokenFoundLocally, accessTokenExpired, accessTokenInvalid
+    ( docs, failures, fields
+    , accessTokenFoundLocally, accessTokenExpired, accessTokenInvalid
     , versionsFoundLocally, versionsReceived, versionsFailedToDecode
     , unsupportedVersionForEndpoint
-    , decodedDictSize, leakingValueFound
+    , decodedDictSize, invalidHashInHashdict, invalidHashInMashdict, leakingValueFound
     )
 
 {-| Throughout the Elm SDK, there are lots of pieces of text being used for
@@ -24,6 +25,11 @@ This is a risky feature, keep in mind that even a patch update might break this!
 You should only do this if you know what you're doing.
 
 
+## Type documentation
+
+@docs docs, failures, fields
+
+
 ## API Authentication
 
 Messages sent as API logs during the authentication phase of the API
@@ -53,11 +59,19 @@ Messages sent as API logs during communication with the API.
 
 Messages sent as API logs when a JSON value is being decoded.
 
-@docs decodedDictSize, leakingValueFound
+@docs decodedDictSize, invalidHashInHashdict, invalidHashInMashdict, leakingValueFound
 
 -}
 
 
+type alias Desc =
+    List String
+
+
+type alias TypeDocs =
+    { name : String, description : Desc }
+
+
 {-| Logs when the Matrix API returns that an access token is no longer valid.
 -}
 accessTokenExpired : String
@@ -95,6 +109,117 @@ decodedDictSize from to =
         ]
 
 
+{-| Documentation used for all functions and data types in JSON coders
+-}
+docs :
+    { event : TypeDocs
+    , hashdict : TypeDocs
+    , mashdict : TypeDocs
+    , stateManager : TypeDocs
+    , unsigned : TypeDocs
+    }
+docs =
+    { event =
+        { name = "Event"
+        , description =
+            [ "The Event type represents a single value that contains all the information for a single event in the room."
+            ]
+        }
+    , hashdict =
+        { name = "Hashdict"
+        , description =
+            [ "This allows you to store values based on an externally defined identifier."
+            , "For example, the hashdict can store events and use their event id as their key."
+            ]
+        }
+    , mashdict =
+        { name = "Mashdict"
+        , description =
+            [ "The mashdict exclusively stores values for which the hashing algorithm returns a value, and it ignores the outcome for all other scenarios."
+            ]
+        }
+    , stateManager =
+        { name = "StateManager"
+        , description =
+            [ "The StateManager tracks the room state based on events, their event types and the optional state keys they provide."
+            , "Instead of making the user loop through the room's timeline of events, the StateManager offers the user a dictionary-like experience to navigate through the Matrix room state."
+            ]
+        }
+    , unsigned =
+        { name = "Unsigned Data"
+        , description =
+            [ "Unsigned data is optional data that might come along with the event."
+            , "This information is often supportive but not necessary to the context."
+            ]
+        }
+    }
+
+
+{-| Description of all edge cases where a JSON decoder can fail.
+-}
+failures : { hashdict : Desc, mashdict : Desc }
+failures =
+    { hashdict =
+        [ "Not all values map to thir respected hash with the given hash function."
+        ]
+    , mashdict =
+        [ "Not all values map to thir respected hash with the given hash function."
+        ]
+    }
+
+
+
+-- TODO
+
+
+fields :
+    { event :
+        { content : Desc
+        , eventId : Desc
+        , originServerTs : Desc
+        , roomId : Desc
+        , sender : Desc
+        , stateKey : Desc
+        , eventType : Desc
+        , unsigned : Desc
+        }
+    , unsigned :
+        { age : Desc
+        , prevContent : Desc
+        , redactedBecause : Desc
+        , transactionId : Desc
+        }
+    }
+fields =
+    { event =
+        { content = []
+        , eventId = []
+        , originServerTs = []
+        , roomId = []
+        , sender = []
+        , stateKey = []
+        , eventType = []
+        , unsigned = []
+        }
+    , unsigned =
+        { age = []
+        , prevContent = []
+        , redactedBecause = []
+        , transactionId = []
+        }
+    }
+
+
+invalidHashInHashdict : String
+invalidHashInHashdict =
+    "Invalid hash function: not all elements hash to their JSON-stored hashes"
+
+
+invalidHashInMashdict : String
+invalidHashInMashdict =
+    "Invalid hash function: not all elements hash to their JSON-stored hashes"
+
+
 {-| The Elm SDK occassionally uses [leaking values](Internal-Config-Leaks),
 which might indicate exceptional behaviour. As such, this log is sent when one
 of those leaking values is found: to alert the user that something fishy might
diff --git a/src/Internal/Tools/Hashdict.elm b/src/Internal/Tools/Hashdict.elm
index f2e4fdb..3b46f30 100644
--- a/src/Internal/Tools/Hashdict.elm
+++ b/src/Internal/Tools/Hashdict.elm
@@ -4,7 +4,7 @@ module Internal.Tools.Hashdict exposing
     , isEmpty, member, memberKey, get, size, isEqual
     , keys, values, toList, fromList
     , rehash, union
-    , encode, decoder, softDecoder
+    , coder, encode, decoder, softDecoder
     )
 
 {-| This module abstracts the `Dict` type with one function that assigns a
@@ -40,13 +40,14 @@ This allows you to store values based on an externally defined identifier.
 
 ## JSON coders
 
-@docs encode, decoder, softDecoder
+@docs coder, encode, decoder, softDecoder
 
 -}
 
 import FastDict as Dict exposing (Dict)
-import Json.Decode as D
-import Json.Encode as E
+import Internal.Config.Log as Log
+import Internal.Config.Text as Text
+import Internal.Tools.Json as Json
 
 
 {-| A dictionary of keys and values where each key is defined by its value. For
@@ -80,25 +81,41 @@ type Hashdict a
         }
 
 
+coder : (a -> String) -> Json.Coder a -> Json.Coder (Hashdict a)
+coder f c1 =
+    Json.andThen
+        { name = Text.docs.hashdict.name
+        , description = Text.docs.hashdict.description
+        , forth =
+            -- TODO: Implement fastDictWithFilter function
+            \items ->
+                case List.filter (\( k, v ) -> f v /= k) (Dict.toList items) of
+                    [] ->
+                        { hash = f, values = items }
+                            |> Hashdict
+                            |> Json.succeed
+                            |> (|>) []
+
+                    wrongHashes ->
+                        wrongHashes
+                            |> List.map Tuple.first
+                            |> List.map ((++) "Invalid hash")
+                            |> List.map Log.log.error
+                            |> Json.fail Text.invalidHashInHashdict
+        , back = \(Hashdict h) -> h.values
+        , failure =
+            Text.failures.hashdict
+        }
+        (Json.fastDict c1)
+
+
 {-| Decode a hashdict from a JSON value. To create a hashdict, you are expected
 to insert a hash function. If the hash function doesn't properly hash the values
 as expected, the decoder will fail to decode the hashdict.
 -}
-decoder : (a -> String) -> D.Decoder a -> D.Decoder (Hashdict a)
-decoder f xDecoder =
-    D.keyValuePairs xDecoder
-        |> D.andThen
-            (\items ->
-                if List.all (\( hash, value ) -> f value == hash) items then
-                    items
-                        |> Dict.fromList
-                        |> (\d -> { hash = f, values = d })
-                        |> Hashdict
-                        |> D.succeed
-
-                else
-                    D.fail "Hash function fails to properly hash all values"
-            )
+decoder : (a -> String) -> Json.Coder a -> Json.Decoder (Hashdict a)
+decoder f c1 =
+    Json.decode (coder f c1)
 
 
 {-| Create an empty hashdict.
@@ -112,12 +129,9 @@ empty hash =
 cannot be universally converted to JSON, so it is up to you to preserve that
 hash function!
 -}
-encode : (a -> E.Value) -> Hashdict a -> E.Value
-encode encodeX (Hashdict h) =
-    h.values
-        |> Dict.toList
-        |> List.map (Tuple.mapSecond encodeX)
-        |> E.object
+encode : Json.Coder a -> Json.Encoder (Hashdict a)
+encode c1 (Hashdict h) =
+    Json.encode (coder h.hash c1) (Hashdict h)
 
 
 {-| Convert an association list into a hashdict.
@@ -240,10 +254,20 @@ size (Hashdict h) =
 used hash function, (or if you simply do not care) you can use this function to
 decode and rehash the Hashdict using your new hash function.
 -}
-softDecoder : (a -> String) -> D.Decoder a -> D.Decoder (Hashdict a)
-softDecoder f xDecoder =
-    D.keyValuePairs xDecoder
-        |> D.map (List.map Tuple.second >> fromList f)
+softDecoder : (a -> String) -> Json.Coder a -> Json.Decoder (Hashdict a)
+softDecoder f c1 =
+    c1
+        |> Json.fastDict
+        |> Json.map
+            { name = Text.docs.hashdict.name
+            , description = Text.docs.hashdict.description
+            , forth =
+                \items ->
+                    Hashdict { hash = f, values = items }
+                        |> rehash f
+            , back = \(Hashdict h) -> h.values
+            }
+        |> Json.decode
 
 
 {-| Convert a hashdict into an association list of key-value pairs, sorted by
diff --git a/src/Internal/Tools/Mashdict.elm b/src/Internal/Tools/Mashdict.elm
index 22c27a8..7ede8c3 100644
--- a/src/Internal/Tools/Mashdict.elm
+++ b/src/Internal/Tools/Mashdict.elm
@@ -4,7 +4,7 @@ module Internal.Tools.Mashdict exposing
     , isEmpty, member, memberKey, get, size, isEqual
     , keys, values, toList, fromList
     , rehash, union
-    , encode, decoder, softDecoder
+    , coder, encode, decoder, softDecoder
     )
 
 {-|
@@ -48,13 +48,14 @@ In general, you are advised to learn more about the
 
 ## JSON coders
 
-@docs encode, decoder, softDecoder
+@docs coder, encode, decoder, softDecoder
 
 -}
 
 import FastDict as Dict exposing (Dict)
-import Json.Decode as D
-import Json.Encode as E
+import Internal.Config.Log as Log
+import Internal.Config.Text as Text
+import Internal.Tools.Json as Json
 
 
 {-| A dictionary of keys and values where each key is defined by its value, but
@@ -92,25 +93,39 @@ type Mashdict a
         }
 
 
+coder : (a -> Maybe String) -> Json.Coder a -> Json.Coder (Mashdict a)
+coder f c1 =
+    Json.andThen
+        { name = Text.docs.mashdict.name
+        , description = Text.docs.mashdict.description
+        , forth =
+            \items ->
+                case List.filter (\( k, v ) -> f v /= Just k) (Dict.toList items) of
+                    [] ->
+                        { hash = f, values = items }
+                            |> Mashdict
+                            |> Json.succeed
+                            |> (|>) []
+
+                    wrongHashes ->
+                        wrongHashes
+                            |> List.map Tuple.first
+                            |> List.map ((++) "Invalid hash")
+                            |> List.map Log.log.error
+                            |> Json.fail Text.invalidHashInMashdict
+        , back = \(Mashdict h) -> h.values
+        , failure = Text.failures.mashdict
+        }
+        (Json.fastDict c1)
+
+
 {-| Decode a mashdict from a JSON value. To create a mashdict, you are expected
 to insert a hash function. If the hash function doesn't properly hash the values
 as expected, the decoder will fail to decode the mashdict.
 -}
-decoder : (a -> Maybe String) -> D.Decoder a -> D.Decoder (Mashdict a)
-decoder f xDecoder =
-    D.keyValuePairs xDecoder
-        |> D.andThen
-            (\items ->
-                if List.all (\( hash, value ) -> f value == Just hash) items then
-                    items
-                        |> Dict.fromList
-                        |> (\d -> { hash = f, values = d })
-                        |> Mashdict
-                        |> D.succeed
-
-                else
-                    D.fail "Hash function fails to properly hash all values"
-            )
+decoder : (a -> Maybe String) -> Json.Coder a -> Json.Decoder (Mashdict a)
+decoder f c1 =
+    Json.decode (coder f c1)
 
 
 {-| Create an empty mashdict.
@@ -124,12 +139,9 @@ empty hash =
 cannot be universally converted to JSON, so it is up to you to preserve that
 hash function!
 -}
-encode : (a -> E.Value) -> Mashdict a -> E.Value
-encode encodeX (Mashdict h) =
-    h.values
-        |> Dict.toList
-        |> List.map (Tuple.mapSecond encodeX)
-        |> E.object
+encode : Json.Coder a -> Json.Encoder (Mashdict a)
+encode c1 (Mashdict h) =
+    Json.encode (coder h.hash c1) (Mashdict h)
 
 
 {-| Convert an association list into a mashdict.
@@ -266,10 +278,20 @@ size (Mashdict h) =
 used hash function, (or if you simply do not care) you can use this function to
 decode and rehash the Mashdict using your new hash function.
 -}
-softDecoder : (a -> Maybe String) -> D.Decoder a -> D.Decoder (Mashdict a)
-softDecoder f xDecoder =
-    D.keyValuePairs xDecoder
-        |> D.map (List.map Tuple.second >> fromList f)
+softDecoder : (a -> Maybe String) -> Json.Coder a -> Json.Decoder (Mashdict a)
+softDecoder f c1 =
+    c1
+        |> Json.fastDict
+        |> Json.map
+            { name = Text.docs.hashdict.name
+            , description = Text.docs.hashdict.description
+            , forth =
+                \items ->
+                    Mashdict { hash = f, values = items }
+                        |> rehash f
+            , back = \(Mashdict h) -> h.values
+            }
+        |> Json.decode
 
 
 {-| Convert a mashdict into an association list of key-value pairs, sorted by
diff --git a/src/Internal/Tools/Timestamp.elm b/src/Internal/Tools/Timestamp.elm
index a0ed35c..0f96a77 100644
--- a/src/Internal/Tools/Timestamp.elm
+++ b/src/Internal/Tools/Timestamp.elm
@@ -1,6 +1,6 @@
 module Internal.Tools.Timestamp exposing
     ( Timestamp
-    , encode, decoder
+    , coder, encode, decoder
     )
 
 {-| The Timestamp module is a simplification of the Timestamp as delivered by
@@ -14,12 +14,11 @@ elm/time. This module offers ways to work with the timestamp in meaningful ways.
 
 ## JSON coders
 
-@docs encode, decoder
+@docs coder, encode, decoder
 
 -}
 
-import Json.Decode as D
-import Json.Encode as E
+import Internal.Tools.Json as Json
 import Time
 
 
@@ -29,15 +28,30 @@ type alias Timestamp =
     Time.Posix
 
 
+{-| Create a Json coder
+-}
+coder : Json.Coder Timestamp
+coder =
+    Json.map
+        { back = Time.posixToMillis
+        , forth = Time.millisToPosix
+        , name = "Milliseconds to POSIX"
+        , description =
+            [ "Converts the timestamp from milliseconds to a POSIX timestamp."
+            ]
+        }
+        Json.int
+
+
 {-| Encode a timestamp into a JSON value.
 -}
-encode : Timestamp -> E.Value
+encode : Json.Encoder Timestamp
 encode =
-    Time.posixToMillis >> E.int
+    Json.encode coder
 
 
 {-| Decode a timestamp from a JSON value.
 -}
-decoder : D.Decoder Timestamp
+decoder : Json.Decoder Timestamp
 decoder =
-    D.map Time.millisToPosix D.int
+    Json.decode coder
diff --git a/src/Internal/Values/Event.elm b/src/Internal/Values/Event.elm
index b27848d..304e7cb 100644
--- a/src/Internal/Values/Event.elm
+++ b/src/Internal/Values/Event.elm
@@ -1,7 +1,7 @@
 module Internal.Values.Event exposing
     ( Event
     , UnsignedData(..), age, prevContent, redactedBecause, transactionId
-    , encode, decoder
+    , coder, encode, decoder
     )
 
 {-|
@@ -22,22 +22,20 @@ of a room.
 
 ## JSON Coder
 
-@docs encode, decoder
+@docs coder, encode, decoder
 
 -}
 
 import Internal.Config.Default as Default
-import Internal.Tools.DecodeExtra as D
-import Internal.Tools.EncodeExtra as E
+import Internal.Config.Text as Text
+import Internal.Tools.Json as Json
 import Internal.Tools.Timestamp as Timestamp exposing (Timestamp)
-import Json.Decode as D
-import Json.Encode as E
 
 
 {-| The Event type occurs everywhere on a user's timeline.
 -}
 type alias Event =
-    { content : E.Value
+    { content : Json.Value
     , eventId : String
     , originServerTs : Timestamp
     , roomId : String
@@ -54,7 +52,7 @@ helper functions.
 type UnsignedData
     = UnsignedData
         { age : Maybe Int
-        , prevContent : Maybe E.Value
+        , prevContent : Maybe Json.Value
         , redactedBecause : Maybe Event
         , transactionId : Maybe String
         }
@@ -67,66 +65,93 @@ age event =
     Maybe.andThen (\(UnsignedData data) -> data.age) event.unsigned
 
 
+coder : Json.Coder Event
+coder =
+    Json.object8
+        { name = Text.docs.event.name
+        , description = Text.docs.event.description
+        , init = Event
+        }
+        (Json.field.required
+            { fieldName = "content"
+            , toField = .content
+            , description = Text.fields.event.content
+            , coder = Json.value
+            }
+        )
+        (Json.field.required
+            { fieldName = "eventId"
+            , toField = .eventId
+            , description = Text.fields.event.eventId
+            , coder = Json.string
+            }
+        )
+        (Json.field.required
+            { fieldName = "originServerTs"
+            , toField = .originServerTs
+            , description = Text.fields.event.originServerTs
+            , coder = Timestamp.coder
+            }
+        )
+        (Json.field.required
+            { fieldName = "roomId"
+            , toField = .roomId
+            , description = Text.fields.event.roomId
+            , coder = Json.string
+            }
+        )
+        (Json.field.required
+            { fieldName = "sender"
+            , toField = .sender
+            , description = Text.fields.event.sender
+            , coder = Json.string
+            }
+        )
+        (Json.field.optional.value
+            { fieldName = "stateKey"
+            , toField = .stateKey
+            , description = Text.fields.event.stateKey
+            , coder = Json.string
+            }
+        )
+        (Json.field.required
+            -- NOTE! | In JSON we call it `type`, not `eventType`,
+            -- NOTE! | so that the data is easier to read for other non-Elm
+            -- NOTE! | JSON parsers
+            { fieldName = "type"
+            , toField = .eventType
+            , description = Text.fields.event.eventType
+            , coder = Json.string
+            }
+        )
+        (Json.field.optional.value
+            { fieldName = "unsigned"
+            , toField = .unsigned
+            , description = Text.fields.event.unsigned
+            , coder = unsignedCoder
+            }
+        )
+
+
 {-| Decode an Event from a JSON value.
 -}
-decoder : D.Decoder Event
+decoder : Json.Decoder Event
 decoder =
-    D.map8 Event
-        (D.field "content" D.value)
-        (D.field "eventId" D.string)
-        (D.field "originServerTs" Timestamp.decoder)
-        (D.field "roomId" D.string)
-        (D.field "sender" D.string)
-        (D.opField "stateKey" D.string)
-        (D.field "eventType" D.string)
-        (D.opField "unsigned" decoderUnsignedData)
-
-
-{-| Decode Unsigned Data from a JSON value.
--}
-decoderUnsignedData : D.Decoder UnsignedData
-decoderUnsignedData =
-    D.map4 (\a b c d -> UnsignedData { age = a, prevContent = b, redactedBecause = c, transactionId = d })
-        (D.opField "age" D.int)
-        (D.opField "prevContent" D.value)
-        (D.opField "redactedBecause" (D.lazy (\_ -> decoder)))
-        (D.opField "transactionId" D.string)
+    Json.decode coder
 
 
 {-| Encode an Event into a JSON value.
 -}
-encode : Event -> E.Value
-encode event =
-    E.maybeObject
-        [ ( "content", Just event.content )
-        , ( "eventId", Just <| E.string event.eventId )
-        , ( "originServerTs", Just <| Timestamp.encode event.originServerTs )
-        , ( "roomId", Just <| E.string event.roomId )
-        , ( "sender", Just <| E.string event.sender )
-        , ( "stateKey", Maybe.map E.string event.stateKey )
-        , ( "eventType", Just <| E.string event.eventType )
-        , ( "unsigned", Maybe.map encodeUnsignedData event.unsigned )
-        , ( "version", Just <| E.string Default.currentVersion )
-        ]
-
-
-{-| Encode Unsigned Data into a JSON value.
--}
-encodeUnsignedData : UnsignedData -> E.Value
-encodeUnsignedData (UnsignedData data) =
-    E.maybeObject
-        [ ( "age", Maybe.map E.int data.age )
-        , ( "prevContent", data.prevContent )
-        , ( "redactedBecause", Maybe.map encode data.redactedBecause )
-        , ( "transactionId", Maybe.map E.string data.transactionId )
-        ]
+encode : Json.Encoder Event
+encode =
+    Json.encode coder
 
 
 {-| Determine the previous `content` value for this event. This field is only a
 `Just value` if the event is a state event, and the Matrix Vault has permission
 to see the previous content.
 -}
-prevContent : Event -> Maybe E.Value
+prevContent : Event -> Maybe Json.Value
 prevContent event =
     Maybe.andThen (\(UnsignedData data) -> data.prevContent) event.unsigned
 
@@ -145,3 +170,40 @@ display the original transaction id used for the event.
 transactionId : Event -> Maybe String
 transactionId event =
     Maybe.andThen (\(UnsignedData data) -> data.transactionId) event.unsigned
+
+
+unsignedCoder : Json.Coder UnsignedData
+unsignedCoder =
+    Json.object4
+        { name = Text.docs.unsigned.name
+        , description = Text.docs.unsigned.description
+        , init = \a b c d -> UnsignedData { age = a, prevContent = b, redactedBecause = c, transactionId = d }
+        }
+        (Json.field.optional.value
+            { fieldName = "age"
+            , toField = \(UnsignedData data) -> data.age
+            , description = Text.fields.unsigned.age
+            , coder = Json.int
+            }
+        )
+        (Json.field.optional.value
+            { fieldName = "prevContent"
+            , toField = \(UnsignedData data) -> data.prevContent
+            , description = Text.fields.unsigned.prevContent
+            , coder = Json.value
+            }
+        )
+        (Json.field.optional.value
+            { fieldName = "redactedBecause"
+            , toField = \(UnsignedData data) -> data.redactedBecause
+            , description = Text.fields.unsigned.redactedBecause
+            , coder = Json.lazy (\_ -> coder)
+            }
+        )
+        (Json.field.optional.value
+            { fieldName = "transactionId"
+            , toField = \(UnsignedData data) -> data.transactionId
+            , description = Text.fields.unsigned.transactionId
+            , coder = Json.string
+            }
+        )
diff --git a/src/Internal/Values/StateManager.elm b/src/Internal/Values/StateManager.elm
index 46282aa..635470a 100644
--- a/src/Internal/Values/StateManager.elm
+++ b/src/Internal/Values/StateManager.elm
@@ -3,7 +3,7 @@ module Internal.Values.StateManager exposing
     , empty, singleton, insert, remove, append
     , isEmpty, member, memberKey, get, size, isEqual
     , keys, values, fromList, toList
-    , encode, decoder
+    , coder, encode, decoder
     )
 
 {-| The StateManager tracks the room state based on events, their event types
@@ -34,15 +34,15 @@ dictionary-like experience to navigate through the Matrix room state.
 
 ## JSON coders
 
-@docs encode, decoder
+@docs coder, encode, decoder
 
 -}
 
 import FastDict as Dict exposing (Dict)
+import Internal.Config.Text as Text
+import Internal.Tools.Json as Json
 import Internal.Tools.Mashdict as Mashdict exposing (Mashdict)
 import Internal.Values.Event as Event exposing (Event)
-import Json.Decode as D
-import Json.Encode as E
 
 
 {-| The StateManager manages the room state by gathering events and looking at
@@ -93,15 +93,24 @@ cleanKey key (StateManager manager) =
         |> StateManager
 
 
+coder : Json.Coder StateManager
+coder =
+    Event.coder
+        |> Mashdict.coder .stateKey
+        |> Json.fastDict
+        |> Json.map
+            { name = Text.docs.stateManager.name
+            , description = Text.docs.stateManager.description
+            , forth = StateManager
+            , back = \(StateManager manager) -> manager
+            }
+
+
 {-| Decode a StateManager from a JSON value.
 -}
-decoder : D.Decoder StateManager
+decoder : Json.Decoder StateManager
 decoder =
-    Event.decoder
-        |> Mashdict.decoder .stateKey
-        |> D.keyValuePairs
-        |> D.map Dict.fromList
-        |> D.map StateManager
+    Json.decode coder
 
 
 {-| Create an empty StateManager.
@@ -113,11 +122,9 @@ empty =
 
 {-| Encode a StateManager into a JSON value.
 -}
-encode : StateManager -> E.Value
-encode (StateManager manager) =
-    manager
-        |> Dict.toCoreDict
-        |> E.dict identity (Mashdict.encode Event.encode)
+encode : Json.Encoder StateManager
+encode =
+    Json.encode coder
 
 
 {-| Build a StateManager using a list of events.
diff --git a/tests/Test/Tools/Hashdict.elm b/tests/Test/Tools/Hashdict.elm
index 500503c..cdfdf43 100644
--- a/tests/Test/Tools/Hashdict.elm
+++ b/tests/Test/Tools/Hashdict.elm
@@ -3,6 +3,7 @@ module Test.Tools.Hashdict exposing (..)
 import Expect
 import Fuzz exposing (Fuzzer)
 import Internal.Tools.Hashdict as Hashdict exposing (Hashdict)
+import Internal.Tools.Json as Json
 import Internal.Values.Event as Event
 import Json.Decode as D
 import Json.Encode as E
@@ -93,11 +94,11 @@ suite =
                 "JSON encode -> JSON decode"
                 (\indent ->
                     Hashdict.empty identity
-                        |> Hashdict.encode E.string
+                        |> Json.encode (Hashdict.coder identity Json.string)
                         |> E.encode indent
-                        |> D.decodeString (Hashdict.decoder identity D.string)
-                        |> Result.map (Hashdict.isEqual (Hashdict.empty String.toUpper))
-                        |> Expect.equal (Ok True)
+                        |> D.decodeString (Json.decode <| Hashdict.coder identity Json.string)
+                        |> Result.map (Tuple.mapFirst (Hashdict.isEqual (Hashdict.empty String.toUpper)))
+                        |> Expect.equal (Ok ( True, [] ))
                 )
             ]
         , describe "singleton"
@@ -164,11 +165,11 @@ suite =
                 "JSON encode -> JSON decode"
                 (\hashdict indent ->
                     hashdict
-                        |> Hashdict.encode Event.encode
+                        |> Json.encode (Hashdict.coder .eventId Event.coder)
                         |> E.encode indent
-                        |> D.decodeString (Hashdict.decoder .eventId Event.decoder)
-                        |> Result.map Hashdict.toList
-                        |> Expect.equal (Ok <| Hashdict.toList hashdict)
+                        |> D.decodeString (Json.decode <| Hashdict.coder .eventId Event.coder)
+                        |> Result.map (Tuple.mapFirst Hashdict.toList)
+                        |> Expect.equal (Ok ( Hashdict.toList hashdict, [] ))
                 )
             ]
         ]
diff --git a/tests/Test/Tools/Mashdict.elm b/tests/Test/Tools/Mashdict.elm
index dfddc6c..0425dc0 100644
--- a/tests/Test/Tools/Mashdict.elm
+++ b/tests/Test/Tools/Mashdict.elm
@@ -2,6 +2,7 @@ module Test.Tools.Mashdict exposing (..)
 
 import Expect
 import Fuzz exposing (Fuzzer)
+import Internal.Tools.Json as Json
 import Internal.Tools.Mashdict as Mashdict exposing (Mashdict)
 import Internal.Values.Event as Event
 import Json.Decode as D
@@ -93,11 +94,11 @@ suite =
                 "JSON encode -> JSON decode"
                 (\indent ->
                     Mashdict.empty Just
-                        |> Mashdict.encode E.string
+                        |> Json.encode (Mashdict.coder Just Json.string)
                         |> E.encode indent
-                        |> D.decodeString (Mashdict.decoder Just D.string)
-                        |> Result.map (Mashdict.isEqual (Mashdict.empty Just))
-                        |> Expect.equal (Ok True)
+                        |> D.decodeString (Json.decode <| Mashdict.coder Just Json.string)
+                        |> Result.map (Tuple.mapFirst <| Mashdict.isEqual (Mashdict.empty Just))
+                        |> Expect.equal (Ok ( True, [] ))
                 )
             ]
         , describe "singleton"
@@ -194,11 +195,11 @@ suite =
                 "JSON encode -> JSON decode"
                 (\hashdict indent ->
                     hashdict
-                        |> Mashdict.encode Event.encode
+                        |> Json.encode (Mashdict.coder .stateKey Event.coder)
                         |> E.encode indent
-                        |> D.decodeString (Mashdict.decoder .stateKey Event.decoder)
-                        |> Result.map Mashdict.toList
-                        |> Expect.equal (Ok <| Mashdict.toList hashdict)
+                        |> D.decodeString (Json.decode <| Mashdict.coder .stateKey Event.coder)
+                        |> Result.map (Tuple.mapFirst Mashdict.toList)
+                        |> Expect.equal (Ok ( Mashdict.toList hashdict, [] ))
                 )
             ]
         ]
diff --git a/tests/Test/Tools/Timestamp.elm b/tests/Test/Tools/Timestamp.elm
index d98cafb..5721821 100644
--- a/tests/Test/Tools/Timestamp.elm
+++ b/tests/Test/Tools/Timestamp.elm
@@ -26,7 +26,7 @@ suite =
                         |> Timestamp.encode
                         |> E.encode indent
                         |> D.decodeString Timestamp.decoder
-                        |> Expect.equal (Ok time)
+                        |> Expect.equal (Ok ( time, [] ))
                 )
             , fuzz fuzzer
                 "JSON decode -> millis"
@@ -42,7 +42,7 @@ suite =
                     n
                         |> E.int
                         |> D.decodeValue Timestamp.decoder
-                        |> Expect.equal (Ok <| Time.millisToPosix n)
+                        |> Expect.equal (Ok ( Time.millisToPosix n, [] ))
                 )
             ]
         , describe "Identity"
diff --git a/tests/Test/Values/StateManager.elm b/tests/Test/Values/StateManager.elm
index ec15032..7e0839e 100644
--- a/tests/Test/Values/StateManager.elm
+++ b/tests/Test/Values/StateManager.elm
@@ -84,7 +84,7 @@ suite =
                     |> StateManager.encode
                     |> E.encode 0
                     |> D.decodeString StateManager.decoder
-                    |> Expect.equal (Ok StateManager.empty)
+                    |> Expect.equal (Ok ( StateManager.empty, [] ))
                     |> always
                 )
             ]