diff --git a/java-classfile.cabal b/java-classfile.cabal
index 892c940..1a05beb 100644
--- a/java-classfile.cabal
+++ b/java-classfile.cabal
@@ -47,6 +47,7 @@ library
       array
     , base >=4.7 && <5
     , bytestring
+    , text
   default-language: Haskell2010
 
 executable java-classfile-exe
@@ -63,6 +64,7 @@ executable java-classfile-exe
     , base >=4.7 && <5
     , bytestring
     , java-classfile
+    , text
   default-language: Haskell2010
 
 test-suite java-classfile-test
@@ -80,4 +82,5 @@ test-suite java-classfile-test
     , base >=4.7 && <5
     , bytestring
     , java-classfile
+    , text
   default-language: Haskell2010
diff --git a/package.yaml b/package.yaml
index c598af9..4789b6a 100644
--- a/package.yaml
+++ b/package.yaml
@@ -23,6 +23,7 @@ dependencies:
 - array
 - base >= 4.7 && < 5
 - bytestring
+- text
 
 ghc-options:
 - -Wall
diff --git a/src/Language/Java/Classfile/ConstantPool/Entry.hs b/src/Language/Java/Classfile/ConstantPool/Entry.hs
index fe59852..e8b5ef7 100644
--- a/src/Language/Java/Classfile/ConstantPool/Entry.hs
+++ b/src/Language/Java/Classfile/ConstantPool/Entry.hs
@@ -1,15 +1,25 @@
 {-# LANGUAGE DerivingVia #-}
 {-# LANGUAGE DeriveGeneric #-}
 {-# LANGUAGE DataKinds #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE InstanceSigs #-}
 module Language.Java.Classfile.ConstantPool.Entry (Entry(..)) where
 import GHC.Generics (Generic, Generically(..))
-import Language.Java.Classfile.Extractable (Extractable)
+import Language.Java.Classfile.Extractable (Extractable (extract))
 import Language.Java.Classfile.Extractable.WithTag (Word8Tag)
 import Language.Java.Classfile.ConstantPool.References (Utf8Reference, ClassReference, NameAndTypeReference, MethodHandleReferenceKind, OpaqueReference, BootstrapMethodIndex)
 import Data.Int (Int32, Int64)
+import Data.Word (Word16)
+import Data.Text (Text)
+import Language.Java.Classfile.Extract (Extract, bytes)
+import qualified Data.Text.Encoding as Text
+import qualified Data.ByteString.Lazy as ByteString
+import qualified Data.ByteString as StrictByteString
 
 data Entry 
-  = Integer             (Word8Tag 3  Int32)
+  = Utf8                (Word8Tag 1  (SizedText Word16))
+  | Integer             (Word8Tag 3  Int32)
   | Float               (Word8Tag 4  Float)
   | Long                (Word8Tag 5  Int64)
   | Double              (Word8Tag 6  Double)
@@ -31,3 +41,17 @@ data Entry
 data MethodHandleInfo = MethodHandleInfo MethodHandleReferenceKind OpaqueReference
   deriving stock (Show, Generic)
   deriving Extractable via Generically MethodHandleInfo
+
+newtype SizedText sizeType = SizedText Text
+  deriving stock (Show)
+
+instance (Integral sizeType, Extractable sizeType) => Extractable (SizedText sizeType) where
+  extract :: Extract (SizedText sizeType)
+  extract = do
+    size <- extract @sizeType
+    slice <- StrictByteString.concat . ByteString.toChunks <$> bytes (fromIntegral size) -- TODO: Replace java zeroes with normal zeroes, normalize 2x3 bytes into 4 byte utf8
+
+    case Text.decodeUtf8' slice of
+      Left err -> fail $ show err
+      Right t -> pure $ SizedText t
+
diff --git a/src/Language/Java/Classfile/Extract.hs b/src/Language/Java/Classfile/Extract.hs
index a75ece7..46111cf 100644
--- a/src/Language/Java/Classfile/Extract.hs
+++ b/src/Language/Java/Classfile/Extract.hs
@@ -1,24 +1,45 @@
 {-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE InstanceSigs #-}
-module Language.Java.Classfile.Extract (Extract(), bytes, runExtract, expectRaw, expectEqual) where
+module Language.Java.Classfile.Extract (Extract(), bytes, runExtract, expectRaw, expectEqual, traceType, traceConstructor, traceField, traceIndex) where
 
 import Data.ByteString.Lazy (ByteString)
 import qualified Data.ByteString.Lazy as ByteString
 import Control.Applicative (Alternative (empty, (<|>)))
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Data.Typeable (Typeable, typeOf)
 
-data Extract a = Extract (Continuation a)
+newtype Extract a = Extract (Continuation a)
+  deriving (Functor)
 
 type Continuation a = ByteString -> Reply a
 
+newtype Expected = Expected Text
+  deriving Show
+newtype Actual = Actual Text
+  deriving Show
+newtype TypeName = TypeName Text
+  deriving Show
+
+data Reason
+  = EndOfInput
+  | UnexpectedValue Expected Actual TypeName
+  | Custom Text
+  | Unknown
+  deriving Show
+
+data Trace
+  = InType Text
+  | InConstructor Text
+  | InField Text
+  | AtIndex Word
+  deriving Show
+
 data Reply a
   = Done ByteString a -- rest, result
-  | Fail
+  | Fail [Trace] Reason
   deriving (Functor)
 
-instance Functor Extract where
-  fmap :: (a -> b) -> Extract a -> Extract b
-  fmap f (Extract cont) = Extract $ \ input -> f <$> cont input
-
 instance Applicative Extract where
   pure :: a -> Extract a
   pure x = Extract $ \ rest -> Done rest x
@@ -26,8 +47,8 @@ instance Applicative Extract where
   (<*>) (Extract computeF) (Extract computeX) = Extract $ \ input -> case computeF input of
     Done rest f -> case computeX rest of
       Done rest' x -> Done rest' (f x)
-      Fail -> Fail
-    Fail -> Fail
+      Fail ts r -> Fail ts r
+    Fail ts r -> Fail ts r
 
 instance Monad Extract where
   (>>=) :: Extract a -> (a -> Extract b) -> Extract b
@@ -35,16 +56,20 @@ instance Monad Extract where
     Done rest a -> let
       (Extract computeB) = f a
       in computeB rest
-    Fail -> Fail
+    Fail ts r -> Fail ts r
 
 instance Alternative Extract where
   empty :: Extract a
-  empty = Extract $ const Fail
+  empty = Extract $ const (Fail [] Unknown)
   (<|>) :: Extract a -> Extract a -> Extract a
   (<|>) (Extract left) (Extract right) = Extract $ \ input -> case left input of
-    Fail -> right input
+    Fail _ _ -> right input
     t -> t
 
+instance MonadFail Extract where
+  fail :: String -> Extract a
+  fail = Extract . const . Fail [] . Custom . Text.pack
+
 -- | Get a specified count of bytes. Fail if there are not enough bytes available.
 
 bytes :: Word -> Extract ByteString
@@ -52,22 +77,36 @@ bytes count = Extract $ \ input -> let
   count' = fromIntegral count
   (bs, rest) = ByteString.splitAt count' input
   in if ByteString.length bs /= count'
-    then Fail
+    then Fail [] EndOfInput
     else Done rest bs
 
+-- | Fail if the specified bytestring is not immediately parseable
+
 expectRaw :: ByteString -> Extract ByteString
 expectRaw e = Extract $ \ input -> let
      (actual, rest) = ByteString.splitAt (ByteString.length e) input
      in case actual == e of
        True -> Done rest actual
-       False -> Fail 
+       False -> Fail [] (mismatchReason e actual)
 
-expectEqual :: Eq a => Extract a -> a -> Extract a
+-- | Fail if the Extractor doesn't yield the specified value
+
+expectEqual :: (Eq a, Show a, Typeable a) => Extract a -> a -> Extract a
 expectEqual (Extract computeActual) expected = Extract $ \ input -> case computeActual input of
   Done rest actual -> if actual == expected
     then Done rest actual
-    else Fail
-  Fail -> Fail
+    else Fail [] (mismatchReason expected actual)
+  failed -> failed
+
+mismatchReason :: (Typeable a, Show a) => a -> a -> Reason
+mismatchReason expected actual = UnexpectedValue (Expected expectedText) (Actual actualText) (TypeName typeName)
+  where
+    actualText = textShow actual
+    expectedText = textShow expected
+    typeName = textShow $ typeOf expected
+
+textShow :: Show a => a -> Text
+textShow = Text.pack . show
 
 {- It seems I cannot define a lawful monad instance
 instance Monad Extract where
@@ -77,8 +116,32 @@ instance Monad Extract where
     Fail -> Fail
 -}
 
-runExtract :: ByteString -> Extract b -> Maybe (ByteString, b)
-runExtract string (Extract computation) = case computation string of
-  Fail -> Nothing
-  Done rest x -> Just (rest, x)
+-- | Apply the extractor to the bytestring, returns the result and the rest on success, otherwise a best-effort traceback.
+
+runExtract :: ByteString -> Extract b -> Either (Reason, [Trace]) (ByteString, b)
+runExtract string (Extract computation) = case computation string of
+  Fail trace reason -> Left (reason, trace)
+  Done rest x -> Right (rest, x)
+
+-- | Trace the contained extractor, the backtrace will supply a hint with the given typeName
+
+traceType :: Text -> Extract a -> Extract a
+traceType typeName (Extract computeA) = Extract $ \ input -> case computeA input of
+  Fail ts r -> Fail (InType typeName:ts) r
+  t -> t
+
+traceConstructor :: Text -> Extract a -> Extract a
+traceConstructor conName (Extract computeA) = Extract $ \ input -> case computeA input of
+  Fail ts r -> Fail (InConstructor conName:ts) r
+  t -> t
+
+traceField :: Text -> Extract a -> Extract a
+traceField fieldName (Extract computeA) = Extract $ \ input -> case computeA input of
+  Fail ts r -> Fail (InField fieldName:ts) r
+  t -> t
+
+traceIndex :: Word -> Extract a -> Extract a
+traceIndex index (Extract computeA) = Extract $ \ input -> case computeA input of
+  Fail ts r -> Fail (AtIndex index:ts) r
+  t -> t
 
diff --git a/src/Language/Java/Classfile/Extractable.hs b/src/Language/Java/Classfile/Extractable.hs
index 58f9a5f..0f5d4af 100644
--- a/src/Language/Java/Classfile/Extractable.hs
+++ b/src/Language/Java/Classfile/Extractable.hs
@@ -2,23 +2,29 @@
 {-# LANGUAGE TypeOperators #-}
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE UndecidableInstances #-}
+{-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeApplications #-}
 {-# LANGUAGE StandaloneDeriving #-}
 {-# LANGUAGE DerivingVia #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE DataKinds #-}
 module Language.Java.Classfile.Extractable (Extractable(extract), expectConstant) where
 
-import Language.Java.Classfile.Extract (Extract, bytes, expectEqual)
+import Language.Java.Classfile.Extract (Extract, bytes, expectEqual, traceType, traceConstructor, traceField, traceIndex)
 import Data.Word (Word8, Word16, Word32)
 import qualified Data.ByteString.Lazy as ByteString
 import Data.ByteString.Lazy (ByteString)
 import Data.Bits (Bits(shiftL, (.|.)))
-import GHC.Generics (U1 (U1), (:*:) ((:*:)), (:+:) (L1, R1), M1 (M1), K1 (K1), Generic (Rep, to), Generically (Generically))
+import GHC.Generics (U1 (U1), (:*:) ((:*:)), (:+:) (L1, R1), M1 (M1), K1 (K1), Generic (Rep, to), Generically (Generically), Meta(..))
 import Control.Applicative ((<|>))
 import Data.Array.IArray (Array, listArray, Ix)
-import Control.Monad (replicateM)
+import Control.Monad (forM)
 import Data.Int (Int32, Int64)
-import Language.Java.Classfile.FromBigEndian (FromBigEndian(fromBigEndian))
 import GHC.Float (castWord32ToFloat, castWord64ToDouble)
+import qualified Data.Text as Text
+import GHC.TypeLits (symbolVal, KnownSymbol)
+import Data.Proxy (Proxy(Proxy))
+import Data.Typeable (Typeable)
 
 class Extractable a where
   extract :: Extract a
@@ -29,11 +35,11 @@ instance Extractable Word8 where
 
 instance Extractable Word16 where
   extract :: Extract Word16
-  extract = fromBigEndian . build <$> bytes 2
+  extract = build <$> bytes 2
 
 instance Extractable Word32 where
   extract :: Extract Word32
-  extract = fromBigEndian . build <$> bytes 4
+  extract = build <$> bytes 4
 
 instance Extractable Int32 where
   extract :: Extract Int32
@@ -59,14 +65,14 @@ instance (Extractable index, Extractable element, Ix index, Integral index) => E
   extract :: Extract (Array index element)
   extract = do
     count <- extract
-    elements <- replicateM (fromIntegral count) extract
+    elements <- forM [1..fromIntegral count] $ \ i -> traceIndex i extract
     pure $ listArray (1, count) elements
 
 deriving via Generically () instance Extractable ()
 deriving via Generically (a, b) instance (Extractable a, Extractable b) => Extractable (a, b)
 deriving via Generically (a, b, c) instance (Extractable a, Extractable b, Extractable c) => Extractable (a, b, c)
 
-expectConstant :: (Extractable a, Eq a) => a -> Extract a
+expectConstant :: (Extractable a, Eq a, Show a, Typeable a) => a -> Extract a
 expectConstant = expectEqual extract
 
 build :: (Bits a, Num a) => ByteString -> a
@@ -95,8 +101,24 @@ instance (GenericExtractable l, GenericExtractable r) => GenericExtractable (l :
   genericExtract = liftA2 (:*:) genericExtract genericExtract
 
 -- meta information constructors
-instance GenericExtractable a => GenericExtractable (M1 i c a) where
-  genericExtract :: Extract (M1 i c a i2)
+instance (GenericExtractable a, KnownSymbol name) => GenericExtractable (M1 tag (MetaData name module_ package isNewtype) a) where
+  genericExtract :: Extract (M1 tag (MetaData name module_ package isNewtype) a i)
+  genericExtract = M1 <$> traceType typeName genericExtract
+    where
+      typeName = Text.pack $ symbolVal (Proxy @name)
+
+instance (GenericExtractable a, KnownSymbol name) => GenericExtractable (M1 tag (MetaCons name fixity isRecord) a) where
+  genericExtract :: Extract (M1 tag (MetaCons name fixity isRecord) a i)
+  genericExtract = M1 <$> traceConstructor conName genericExtract
+    where
+      conName = Text.pack $ symbolVal (Proxy @name)
+
+instance (GenericExtractable a, KnownSymbol name) => GenericExtractable (M1 tag (MetaSel (Just name) isUnpacked isStrictSource isStrictCompiler) a) where
+  genericExtract = M1 <$> traceField fieldName genericExtract
+    where
+      fieldName = Text.pack $ symbolVal (Proxy @name)
+
+instance (GenericExtractable a) => GenericExtractable (M1 tag (MetaSel Nothing isUnpacked isStrictSource isStrictCompiler) a) where
   genericExtract = M1 <$> genericExtract
 
 -- fields !! yay
diff --git a/src/Language/Java/Classfile/Extractable/WithTag.hs b/src/Language/Java/Classfile/Extractable/WithTag.hs
index 08a00b8..a3b78f9 100644
--- a/src/Language/Java/Classfile/Extractable/WithTag.hs
+++ b/src/Language/Java/Classfile/Extractable/WithTag.hs
@@ -12,6 +12,7 @@ import GHC.TypeLits (Natural, natVal, KnownNat)
 import Data.Kind (Type)
 import Control.Monad (void)
 import Data.Proxy (Proxy(Proxy))
+import Data.Typeable ( Typeable )
 import Data.Word (Word8)
 
 type Word8Tag value a = WithNumericTag value Word8 a
@@ -20,7 +21,7 @@ type WithNumericTag :: Natural -> Type -> Type -> Type
 newtype WithNumericTag value tagType a = Tagged a
   deriving newtype Show
 
-instance (KnownNat value, Extractable a, Extractable tagType, Eq tagType, Num tagType) => Extractable (WithNumericTag value tagType a) where
+instance (KnownNat value, Extractable a, Extractable tagType, Eq tagType, Num tagType, Show tagType, Typeable tagType) => Extractable (WithNumericTag value tagType a) where
   extract :: Extract (WithNumericTag value tagType a)
   extract = do
     void $ expectConstant @tagType (fromIntegral . natVal $ Proxy @value)
diff --git a/src/Language/Java/Classfile/Magic.hs b/src/Language/Java/Classfile/Magic.hs
index d4c1223..d690c0d 100644
--- a/src/Language/Java/Classfile/Magic.hs
+++ b/src/Language/Java/Classfile/Magic.hs
@@ -5,10 +5,15 @@ import Language.Java.Classfile.Extractable (Extractable, extract, expectConstant
 import Language.Java.Classfile.Extract (Extract)
 import Data.Hex (Hex (Hex))
 
-data Magic = Magic (Hex Word32)
+newtype Magic = Magic (Hex Word32)
   deriving Show
 
 instance Extractable Magic where
   extract :: Extract Magic
   extract = Magic . Hex <$> expectConstant 0xCAFEBABE
 
+-- >>> :set -XOverloadedLists
+-- >>> import Language.Java.Classfile.Extract (runExtract)
+-- >>> runExtract [0xCA, 0xFE, 0xBA, 0xBE] (Hex <$> (extract :: Extract (Word32)))
+-- Just ("",Hex 0xbebafeca)
+