diff --git a/src/Juvix/Compiler/Asm/Extra/Memory.hs b/src/Juvix/Compiler/Asm/Extra/Memory.hs
index 729940469f..9b3997301b 100644
--- a/src/Juvix/Compiler/Asm/Extra/Memory.hs
+++ b/src/Juvix/Compiler/Asm/Extra/Memory.hs
@@ -110,6 +110,7 @@ getConstantType = \case
   ConstUnit -> TyUnit
   ConstVoid -> TyVoid
   ConstUInt8 {} -> mkTypeUInt8
+  ConstByteArray {} -> TyByteArray
 
 getValueType' :: (Member (Error AsmError) r) => Maybe Location -> InfoTable -> Memory -> Value -> Sem r Type
 getValueType' loc tab mem = \case
diff --git a/src/Juvix/Compiler/Asm/Translation/FromTree.hs b/src/Juvix/Compiler/Asm/Translation/FromTree.hs
index 6974d23d8e..bbe1ab22fe 100644
--- a/src/Juvix/Compiler/Asm/Translation/FromTree.hs
+++ b/src/Juvix/Compiler/Asm/Translation/FromTree.hs
@@ -39,6 +39,7 @@ genCode fi =
       Tree.Binop x -> goBinop isTail x
       Tree.Unop x -> goUnop isTail x
       Tree.Cairo x -> goCairo isTail x
+      Tree.ByteArray {} -> error "ByteArray instructions are not supported in the Asm backend"
       Tree.Anoma {} -> error "Anoma instructions are not supported in the Asm backend"
       Tree.Constant x -> goConstant isTail x
       Tree.MemRef x -> goMemRef isTail x
diff --git a/src/Juvix/Compiler/Backend/C/Translation/FromReg.hs b/src/Juvix/Compiler/Backend/C/Translation/FromReg.hs
index d312c80762..3b4424a6e6 100644
--- a/src/Juvix/Compiler/Backend/C/Translation/FromReg.hs
+++ b/src/Juvix/Compiler/Backend/C/Translation/FromReg.hs
@@ -350,6 +350,7 @@ fromRegInstr bNoStack info = \case
       Reg.ConstUnit -> macroVar "OBJ_UNIT"
       Reg.ConstVoid -> macroVar "OBJ_VOID"
       Reg.ConstUInt8 x -> macroCall "make_smallint" [integer x]
+      Reg.ConstByteArray {} -> impossible
 
     fromPrealloc :: Reg.InstrPrealloc -> Statement
     fromPrealloc Reg.InstrPrealloc {..} =
diff --git a/src/Juvix/Compiler/Backend/Rust/Translation/FromReg.hs b/src/Juvix/Compiler/Backend/Rust/Translation/FromReg.hs
index 274ab200dd..a76a4c4f84 100644
--- a/src/Juvix/Compiler/Backend/Rust/Translation/FromReg.hs
+++ b/src/Juvix/Compiler/Backend/Rust/Translation/FromReg.hs
@@ -251,6 +251,7 @@ fromRegInstr info = \case
       Reg.ConstUnit -> mkVar "OBJ_UNIT"
       Reg.ConstVoid -> mkVar "OBJ_VOID"
       Reg.ConstUInt8 x -> mkCall "make_smallint" [mkInteger x]
+      Reg.ConstByteArray {} -> impossible
 
     fromAlloc :: Reg.InstrAlloc -> [Statement]
     fromAlloc Reg.InstrAlloc {..} =
diff --git a/src/Juvix/Compiler/Builtins.hs b/src/Juvix/Compiler/Builtins.hs
index 2648a6620f..baa336cdf7 100644
--- a/src/Juvix/Compiler/Builtins.hs
+++ b/src/Juvix/Compiler/Builtins.hs
@@ -13,12 +13,14 @@ module Juvix.Compiler.Builtins
     module Juvix.Compiler.Builtins.Anoma,
     module Juvix.Compiler.Builtins.Cairo,
     module Juvix.Compiler.Builtins.Byte,
+    module Juvix.Compiler.Builtins.ByteArray,
   )
 where
 
 import Juvix.Compiler.Builtins.Anoma
 import Juvix.Compiler.Builtins.Bool
 import Juvix.Compiler.Builtins.Byte
+import Juvix.Compiler.Builtins.ByteArray
 import Juvix.Compiler.Builtins.Cairo
 import Juvix.Compiler.Builtins.Control
 import Juvix.Compiler.Builtins.Debug
diff --git a/src/Juvix/Compiler/Builtins/ByteArray.hs b/src/Juvix/Compiler/Builtins/ByteArray.hs
new file mode 100644
index 0000000000..722e937d36
--- /dev/null
+++ b/src/Juvix/Compiler/Builtins/ByteArray.hs
@@ -0,0 +1,27 @@
+module Juvix.Compiler.Builtins.ByteArray where
+
+import Juvix.Compiler.Builtins.Effect
+import Juvix.Compiler.Internal.Extra
+import Juvix.Prelude
+
+registerByteArray :: (Member Builtins r) => AxiomDef -> Sem r ()
+registerByteArray d = do
+  unless (isSmallUniverse' (d ^. axiomType)) (error "ByteArray should be in the small universe")
+  registerBuiltin BuiltinByteArray (d ^. axiomName)
+
+registerByteArrayFromListByte :: (Member Builtins r) => AxiomDef -> Sem r ()
+registerByteArrayFromListByte d = do
+  let loc = getLoc d
+  byte_ <- getBuiltinName loc BuiltinByte
+  list_ <- getBuiltinName loc BuiltinList
+  byteArray <- getBuiltinName loc BuiltinByteArray
+  unless (d ^. axiomType == (list_ @@ byte_ --> byteArray)) (error "bytearray-from-list-byte has the wrong type")
+  registerBuiltin BuiltinByteArrayFromListByte (d ^. axiomName)
+
+registerByteArrayLength :: (Member Builtins r) => AxiomDef -> Sem r ()
+registerByteArrayLength d = do
+  let loc = getLoc d
+  byteArray <- getBuiltinName loc BuiltinByteArray
+  nat_ <- getBuiltinName loc BuiltinNat
+  unless (d ^. axiomType == (byteArray --> nat_)) (error "bytearray-length has the wrong type")
+  registerBuiltin BuiltinByteArrayLength (d ^. axiomName)
diff --git a/src/Juvix/Compiler/Casm/Translation/FromReg.hs b/src/Juvix/Compiler/Casm/Translation/FromReg.hs
index 1cac6232ed..058552dae6 100644
--- a/src/Juvix/Compiler/Casm/Translation/FromReg.hs
+++ b/src/Juvix/Compiler/Casm/Translation/FromReg.hs
@@ -250,6 +250,7 @@ fromReg tab = mkResult $ run $ runLabelInfoBuilderWithNextId (Reg.getNextSymbolI
           Reg.ConstVoid -> 0
           Reg.ConstString {} -> unsupported "strings"
           Reg.ConstUInt8 {} -> unsupported "uint8"
+          Reg.ConstByteArray {} -> unsupported "bytearray"
 
         mkLoad :: Reg.ConstrField -> Sem r RValue
         mkLoad Reg.ConstrField {..} = do
diff --git a/src/Juvix/Compiler/Concrete/Data/Builtins.hs b/src/Juvix/Compiler/Concrete/Data/Builtins.hs
index 6adf2536c3..698aab0a47 100644
--- a/src/Juvix/Compiler/Concrete/Data/Builtins.hs
+++ b/src/Juvix/Compiler/Concrete/Data/Builtins.hs
@@ -222,6 +222,9 @@ data BuiltinAxiom
   | BuiltinByteEq
   | BuiltinByteToNat
   | BuiltinByteFromNat
+  | BuiltinByteArray
+  | BuiltinByteArrayFromListByte
+  | BuiltinByteArrayLength
   deriving stock (Show, Eq, Ord, Enum, Bounded, Generic, Data)
 
 instance HasNameKind BuiltinAxiom where
@@ -263,7 +266,9 @@ instance HasNameKind BuiltinAxiom where
     BuiltinByteEq -> KNameFunction
     BuiltinByteToNat -> KNameFunction
     BuiltinByteFromNat -> KNameFunction
-
+    BuiltinByteArray -> KNameInductive
+    BuiltinByteArrayFromListByte -> KNameFunction
+    BuiltinByteArrayLength -> KNameFunction
   getNameKindPretty :: BuiltinAxiom -> NameKind
   getNameKindPretty = getNameKind
 
@@ -312,6 +317,9 @@ instance Pretty BuiltinAxiom where
     BuiltinByteEq -> Str.byteEq
     BuiltinByteToNat -> Str.byteToNat
     BuiltinByteFromNat -> Str.byteFromNat
+    BuiltinByteArray -> Str.byteArray
+    BuiltinByteArrayFromListByte -> Str.byteArrayFromListByte
+    BuiltinByteArrayLength -> Str.byteArrayLength
 
 data BuiltinType
   = BuiltinTypeInductive BuiltinInductive
diff --git a/src/Juvix/Compiler/Core/Data/InfoTableBuilder.hs b/src/Juvix/Compiler/Core/Data/InfoTableBuilder.hs
index 26f84b00bf..9648fc97d2 100644
--- a/src/Juvix/Compiler/Core/Data/InfoTableBuilder.hs
+++ b/src/Juvix/Compiler/Core/Data/InfoTableBuilder.hs
@@ -288,6 +288,17 @@ declareMaybeBuiltins = do
       (tagJust, "just", mkPi' mkDynamic', Just BuiltinMaybeJust)
     ]
 
+declareListBuiltins :: (Member InfoTableBuilder r) => Sem r ()
+declareListBuiltins = do
+  tagNil <- freshTag
+  tagCons <- freshTag
+  declareInductiveBuiltins
+    "BuiltinList"
+    (Just (BuiltinTypeInductive BuiltinList))
+    [ (tagNil, "builtinListNil", mkPis' [mkSmallUniv], Just BuiltinListNil),
+      (tagCons, "builtinListCons", \x -> mkPis' [mkSmallUniv, mkDynamic', x] x, Just BuiltinListCons)
+    ]
+
 reserveLiteralIntToNatSymbol :: (Member InfoTableBuilder r) => Sem r ()
 reserveLiteralIntToNatSymbol = do
   sym <- freshSymbol
diff --git a/src/Juvix/Compiler/Core/Evaluator.hs b/src/Juvix/Compiler/Core/Evaluator.hs
index b30f90b581..38fcbb0345 100644
--- a/src/Juvix/Compiler/Core/Evaluator.hs
+++ b/src/Juvix/Compiler/Core/Evaluator.hs
@@ -2,6 +2,7 @@ module Juvix.Compiler.Core.Evaluator where
 
 import Control.Exception qualified as Exception
 import Crypto.Sign.Ed25519 qualified as E
+import Data.ByteString qualified as BS
 import Data.HashMap.Strict qualified as HashMap
 import Data.Serialize qualified as S
 import GHC.Base (seq)
@@ -215,6 +216,8 @@ geval opts herr tab env0 = eval' env0
       OpRandomEcPoint -> randomEcPointOp
       OpUInt8ToInt -> uint8ToIntOp
       OpUInt8FromInt -> uint8FromIntOp
+      OpByteArrayFromListByte -> byteArrayFromListByteOp
+      OpByteArrayLength -> byteArrayLengthOp
       where
         err :: Text -> a
         err msg = evalError msg n
@@ -533,6 +536,30 @@ geval opts herr tab env0 = eval' env0
                   . uint8FromNode
                   $ v
         {-# INLINE uint8ToIntOp #-}
+
+        byteArrayFromListByteOp :: [Node] -> Node
+        byteArrayFromListByteOp =
+          unary $ \node ->
+            let !v = eval' env node
+             in nodeFromByteString
+                  . BS.pack
+                  . fromMaybe (evalError "expected list byte" v)
+                  . listUInt8FromNode
+                  $ v
+        {-# INLINE byteArrayFromListByteOp #-}
+
+        byteArrayLengthOp :: [Node] -> Node
+        byteArrayLengthOp =
+          unary $ \node ->
+            let !v = eval' env node
+             in nodeFromInteger
+                  . fromIntegral
+                  . BS.length
+                  . fromMaybe (evalError "expected bytearray" v)
+                  . byteArrayFromNode
+                  $ v
+        {-# INLINE byteArrayLengthOp #-}
+
     {-# INLINE applyBuiltin #-}
 
     -- secretKey, publicKey are not encoded with their length as
@@ -558,6 +585,10 @@ geval opts herr tab env0 = eval' env0
     nodeFromUInt8 !w = mkConstant' (ConstUInt8 w)
     {-# INLINE nodeFromUInt8 #-}
 
+    nodeFromByteString :: ByteString -> Node
+    nodeFromByteString !b = mkConstant' (ConstByteArray b)
+    {-# INLINE nodeFromByteString #-}
+
     nodeFromBool :: Bool -> Node
     nodeFromBool b = mkConstr' (BuiltinTag tag) []
       where
@@ -567,10 +598,10 @@ geval opts herr tab env0 = eval' env0
     {-# INLINE nodeFromBool #-}
 
     mkBuiltinConstructor :: BuiltinConstructor -> [Node] -> Maybe Node
-    mkBuiltinConstructor ctor args =
-      (\tag -> mkConstr' tag args)
-        . (^. constructorTag)
-        <$> lookupTabBuiltinConstructor tab ctor
+    mkBuiltinConstructor ctor args = (\tag -> mkConstr' tag args) <$> builtinConstructorTag ctor
+
+    builtinConstructorTag :: BuiltinConstructor -> Maybe Tag
+    builtinConstructorTag ctor = (^. constructorTag) <$> lookupTabBuiltinConstructor tab ctor
 
     nodeMaybeNothing :: Node
     nodeMaybeNothing =
@@ -611,6 +642,29 @@ geval opts herr tab env0 = eval' env0
       _ -> Nothing
     {-# INLINE uint8FromNode #-}
 
+    byteArrayFromNode :: Node -> Maybe ByteString
+    byteArrayFromNode = \case
+      NCst (Constant _ (ConstByteArray b)) -> Just b
+      _ -> Nothing
+    {-# INLINE byteArrayFromNode #-}
+
+    listUInt8FromNode :: Node -> Maybe [Word8]
+    listUInt8FromNode = \case
+      NCtr (Constr _ t xs) -> do
+        consTag <- builtinConstructorTag BuiltinListCons
+        nilTag <- builtinConstructorTag BuiltinListNil
+        if
+            | t == nilTag -> return []
+            | t == consTag -> case (filter (not . isType') xs) of
+                (hd : tl) -> do
+                  uint8Hd <- uint8FromNode hd
+                  uint8Tl <- concatMapM listUInt8FromNode tl
+                  return (uint8Hd : uint8Tl)
+                _ -> Nothing
+            | otherwise -> Nothing
+      _ -> Nothing
+    {-# INLINE listUInt8FromNode #-}
+
     printNode :: Node -> Text
     printNode = \case
       NCst (Constant _ (ConstString s)) -> s
diff --git a/src/Juvix/Compiler/Core/Extra/Base.hs b/src/Juvix/Compiler/Core/Extra/Base.hs
index d4b1bf6072..b2e0f2c838 100644
--- a/src/Juvix/Compiler/Core/Extra/Base.hs
+++ b/src/Juvix/Compiler/Core/Extra/Base.hs
@@ -200,6 +200,12 @@ mkTypeUInt8 i = mkTypePrim i primitiveUInt8
 mkTypeUInt8' :: Type
 mkTypeUInt8' = mkTypeUInt8 Info.empty
 
+mkTypeByteArray :: Info -> Type
+mkTypeByteArray i = mkTypePrim i PrimByteArray
+
+mkTypeByteArray' :: Type
+mkTypeByteArray' = mkTypeByteArray Info.empty
+
 mkDynamic :: Info -> Type
 mkDynamic i = NDyn (DynamicTy i)
 
diff --git a/src/Juvix/Compiler/Core/Extra/Utils.hs b/src/Juvix/Compiler/Core/Extra/Utils.hs
index 5c4c573a05..a57b0c4e26 100644
--- a/src/Juvix/Compiler/Core/Extra/Utils.hs
+++ b/src/Juvix/Compiler/Core/Extra/Utils.hs
@@ -435,6 +435,8 @@ builtinOpArgTypes = \case
   OpRandomEcPoint -> []
   OpUInt8ToInt -> [mkTypeUInt8']
   OpUInt8FromInt -> [mkTypeInteger']
+  OpByteArrayFromListByte -> [mkDynamic']
+  OpByteArrayLength -> [mkTypeByteArray']
 
 translateCase :: (Node -> Node -> Node -> a) -> a -> Case -> a
 translateCase translateIfFun dflt Case {..} = case _caseBranches of
diff --git a/src/Juvix/Compiler/Core/Keywords.hs b/src/Juvix/Compiler/Core/Keywords.hs
index a2fb2b5e18..6f1d8eac29 100644
--- a/src/Juvix/Compiler/Core/Keywords.hs
+++ b/src/Juvix/Compiler/Core/Keywords.hs
@@ -19,6 +19,8 @@ import Juvix.Data.Keyword.All
     kwBind,
     kwBottom,
     kwBuiltin,
+    kwByteArrayFromListByte,
+    kwByteArrayLength,
     kwCase,
     kwColon,
     kwComma,
diff --git a/src/Juvix/Compiler/Core/Language/Builtins.hs b/src/Juvix/Compiler/Core/Language/Builtins.hs
index c63684c1cd..e4c1cb3d3b 100644
--- a/src/Juvix/Compiler/Core/Language/Builtins.hs
+++ b/src/Juvix/Compiler/Core/Language/Builtins.hs
@@ -38,6 +38,8 @@ data BuiltinOp
   | OpRandomEcPoint
   | OpUInt8ToInt
   | OpUInt8FromInt
+  | OpByteArrayFromListByte
+  | OpByteArrayLength
   deriving stock (Eq, Generic)
 
 instance Serialize BuiltinOp
@@ -94,6 +96,8 @@ builtinOpArgsNum = \case
   OpRandomEcPoint -> 0
   OpUInt8ToInt -> 1
   OpUInt8FromInt -> 1
+  OpByteArrayFromListByte -> 1
+  OpByteArrayLength -> 1
 
 builtinConstrArgsNum :: BuiltinDataTag -> Int
 builtinConstrArgsNum = \case
@@ -139,6 +143,8 @@ builtinIsFoldable = \case
   OpRandomEcPoint -> False
   OpUInt8ToInt -> True
   OpUInt8FromInt -> True
+  OpByteArrayFromListByte -> False
+  OpByteArrayLength -> False
 
 builtinIsCairo :: BuiltinOp -> Bool
 builtinIsCairo op = op `elem` builtinsCairo
@@ -146,6 +152,9 @@ builtinIsCairo op = op `elem` builtinsCairo
 builtinIsAnoma :: BuiltinOp -> Bool
 builtinIsAnoma op = op `elem` builtinsAnoma
 
+builtinIsByteArray :: BuiltinOp -> Bool
+builtinIsByteArray op = op `elem` builtinsByteArray
+
 builtinsString :: [BuiltinOp]
 builtinsString = [OpStrConcat, OpStrToInt, OpShow]
 
@@ -165,3 +174,6 @@ builtinsAnoma =
 
 builtinsUInt8 :: [BuiltinOp]
 builtinsUInt8 = [OpUInt8FromInt, OpUInt8ToInt]
+
+builtinsByteArray :: [BuiltinOp]
+builtinsByteArray = [OpByteArrayFromListByte, OpByteArrayLength]
diff --git a/src/Juvix/Compiler/Core/Language/Nodes.hs b/src/Juvix/Compiler/Core/Language/Nodes.hs
index c956a73a94..833fdcd285 100644
--- a/src/Juvix/Compiler/Core/Language/Nodes.hs
+++ b/src/Juvix/Compiler/Core/Language/Nodes.hs
@@ -39,6 +39,7 @@ data ConstantValue
   | ConstField !FField
   | ConstString !Text
   | ConstUInt8 !Word8
+  | ConstByteArray !ByteString
   deriving stock (Eq, Generic)
 
 -- | Info about a single binder. Associated with Lambda, Pi, Let, Case or Match.
diff --git a/src/Juvix/Compiler/Core/Language/Primitives.hs b/src/Juvix/Compiler/Core/Language/Primitives.hs
index ea008e0a08..9c980d2dd8 100644
--- a/src/Juvix/Compiler/Core/Language/Primitives.hs
+++ b/src/Juvix/Compiler/Core/Language/Primitives.hs
@@ -15,6 +15,7 @@ data Primitive
   | PrimBool PrimBoolInfo
   | PrimString
   | PrimField
+  | PrimByteArray
   deriving stock (Eq, Generic)
 
 primitiveUInt8 :: Primitive
diff --git a/src/Juvix/Compiler/Core/Pretty/Base.hs b/src/Juvix/Compiler/Core/Pretty/Base.hs
index f80ee9e32e..987f877be1 100644
--- a/src/Juvix/Compiler/Core/Pretty/Base.hs
+++ b/src/Juvix/Compiler/Core/Pretty/Base.hs
@@ -5,6 +5,7 @@ module Juvix.Compiler.Core.Pretty.Base
   )
 where
 
+import Data.ByteString qualified as BS
 import Data.HashMap.Strict qualified as HashMap
 import Data.Map.Strict qualified as Map
 import Juvix.Compiler.Core.Data.BinderList qualified as BL
@@ -64,6 +65,8 @@ instance PrettyCode BuiltinOp where
     OpRandomEcPoint -> return primRandomEcPoint
     OpUInt8ToInt -> return primUInt8ToInt
     OpUInt8FromInt -> return primFieldFromInt
+    OpByteArrayFromListByte -> return primByteArrayFromListByte
+    OpByteArrayLength -> return primByteArrayLength
 
 instance PrettyCode BuiltinDataTag where
   ppCode = \case
@@ -81,10 +84,12 @@ instance PrettyCode Tag where
 
 instance PrettyCode Primitive where
   ppCode = \case
+    p@(PrimInteger _) | p == primitiveUInt8 -> return $ annotate (AnnKind KNameInductive) (pretty ("UInt8" :: String))
     PrimInteger _ -> return $ annotate (AnnKind KNameInductive) (pretty ("Int" :: String))
     PrimField -> return $ annotate (AnnKind KNameInductive) (pretty ("Field" :: String))
     PrimBool _ -> return $ annotate (AnnKind KNameInductive) (pretty ("Bool" :: String))
     PrimString -> return $ annotate (AnnKind KNameInductive) (pretty ("String" :: String))
+    PrimByteArray -> return $ annotate (AnnKind KNameInductive) (pretty ("ByteArray" :: String))
 
 ppName :: NameKind -> Text -> Sem r (Doc Ann)
 ppName kind name = return $ annotate (AnnKind kind) (pretty name)
@@ -104,6 +109,7 @@ ppCodeVar' name v = do
     else return name'
 
 instance PrettyCode ConstantValue where
+  ppCode :: forall r. (Member (Reader Options) r) => ConstantValue -> Sem r (Doc Ann)
   ppCode = \case
     ConstInteger int ->
       return $ annotate AnnLiteralInteger (pretty int)
@@ -113,13 +119,31 @@ instance PrettyCode ConstantValue where
       return $ annotate AnnLiteralInteger (pretty i)
     ConstString txt ->
       return $ annotate AnnLiteralString (pretty (show txt :: String))
+    ConstByteArray bs -> do
+      let bytes = ConstUInt8 <$> BS.unpack bs
+      codeBs <- mapM ppCode bytes
+      bytesList <- go codeBs
+      op <- ppCode OpByteArrayFromListByte
+      return (op <+> bytesList)
+      where
+        go :: [Doc Ann] -> Sem r (Doc Ann)
+        go xs = do
+          uint8Ty <- ppCode mkTypeUInt8'
+          case xs of
+            [] -> return (parens (kwBuiltinNil <+> uint8Ty))
+            (d : ds) -> do
+              next <- go ds
+              return (parens (kwBuiltinCons <+> uint8Ty <+> d <+> next))
+
+instance PrettyCode Word8 where
+  ppCode i = return (pretty i <> "u8")
 
 instance PrettyCode (Constant' i) where
   ppCode Constant {..} = case _constantValue of
     ConstField fld ->
       return $ annotate AnnLiteralInteger (pretty fld <> "F")
     ConstUInt8 i ->
-      return $ annotate AnnLiteralInteger (pretty i <> "u8")
+      annotate AnnLiteralInteger <$> ppCode i
     _ -> ppCode _constantValue
 
 instance (PrettyCode a, HasAtomicity a) => PrettyCode (App' i a) where
@@ -548,7 +572,7 @@ instance PrettyCode InfoTable where
           shouldPrintInductive :: Maybe BuiltinType -> Bool
           shouldPrintInductive = \case
             Just (BuiltinTypeInductive i) -> case i of
-              BuiltinList -> True
+              BuiltinList -> False
               BuiltinMaybe -> False
               BuiltinPair -> True
               BuiltinPoseidonState -> True
@@ -761,6 +785,12 @@ primUInt8FromInt = primitive Str.itou8
 primFieldToInt :: Doc Ann
 primFieldToInt = primitive Str.ftoi
 
+primByteArrayFromListByte :: Doc Ann
+primByteArrayFromListByte = primitive Str.byteArrayFromListByte
+
+primByteArrayLength :: Doc Ann
+primByteArrayLength = primitive Str.byteArrayLength
+
 primLess :: Doc Ann
 primLess = primitive Str.less
 
@@ -868,3 +898,9 @@ kwBottomAscii = keyword Str.bottomAscii
 
 kwBottom :: Doc Ann
 kwBottom = keyword Str.bottom
+
+kwBuiltinCons :: Doc Ann
+kwBuiltinCons = constructor Str.builtinListCons
+
+kwBuiltinNil :: Doc Ann
+kwBuiltinNil = constructor Str.builtinListNil
diff --git a/src/Juvix/Compiler/Core/Transformation/Check/Base.hs b/src/Juvix/Compiler/Core/Transformation/Check/Base.hs
index 953a57a9be..079662fca4 100644
--- a/src/Juvix/Compiler/Core/Transformation/Check/Base.hs
+++ b/src/Juvix/Compiler/Core/Transformation/Check/Base.hs
@@ -71,6 +71,8 @@ checkBuiltins allowUntypedFail = dmapRM go
                 throw $ unsupportedError "cairo" node (getInfoLocation _builtinAppInfo)
             | _builtinAppOp `elem` builtinsAnoma ->
                 throw $ unsupportedError "anoma" node (getInfoLocation _builtinAppInfo)
+            | _builtinAppOp `elem` builtinsByteArray ->
+                throw $ unsupportedError "bytearray" node (getInfoLocation _builtinAppInfo)
             | otherwise ->
                 return $ Recur node
       _ -> return $ Recur node
diff --git a/src/Juvix/Compiler/Core/Transformation/Check/Cairo.hs b/src/Juvix/Compiler/Core/Transformation/Check/Cairo.hs
index 8b7b3fb7e9..59751aaaf3 100644
--- a/src/Juvix/Compiler/Core/Transformation/Check/Cairo.hs
+++ b/src/Juvix/Compiler/Core/Transformation/Check/Cairo.hs
@@ -12,7 +12,7 @@ checkCairo md = do
   checkMainType
   checkNoAxioms md
   mapAllNodesM checkNoIO md
-  mapAllNodesM (checkBuiltins' (builtinsString ++ builtinsUInt8) [PrimString, primitiveUInt8]) md
+  mapAllNodesM (checkBuiltins' (builtinsString ++ builtinsUInt8 ++ builtinsByteArray) [PrimString, primitiveUInt8, PrimByteArray]) md
   where
     checkMainType :: Sem r ()
     checkMainType =
@@ -60,6 +60,7 @@ checkCairo md = do
           PrimBool {} -> True
           PrimField {} -> True
           PrimString {} -> False
+          PrimByteArray {} -> False
 
         isRecordOrList :: TypeConstr -> Bool
         isRecordOrList TypeConstr {..} = case ii ^. inductiveBuiltin of
diff --git a/src/Juvix/Compiler/Core/Transformation/Check/Exec.hs b/src/Juvix/Compiler/Core/Transformation/Check/Exec.hs
index f11b3265aa..18200f78e1 100644
--- a/src/Juvix/Compiler/Core/Transformation/Check/Exec.hs
+++ b/src/Juvix/Compiler/Core/Transformation/Check/Exec.hs
@@ -10,4 +10,4 @@ checkExec md = do
   checkNoAxioms md
   checkMainExists md
   checkMainTypeExec md
-  mapAllNodesM (checkBuiltins' (builtinsCairo ++ builtinsAnoma) []) md
+  mapAllNodesM (checkBuiltins' (builtinsCairo ++ builtinsAnoma ++ builtinsByteArray) [PrimByteArray]) md
diff --git a/src/Juvix/Compiler/Core/Transformation/ComputeTypeInfo.hs b/src/Juvix/Compiler/Core/Transformation/ComputeTypeInfo.hs
index e79b027f47..e2622cf50a 100644
--- a/src/Juvix/Compiler/Core/Transformation/ComputeTypeInfo.hs
+++ b/src/Juvix/Compiler/Core/Transformation/ComputeTypeInfo.hs
@@ -35,6 +35,7 @@ computeNodeTypeInfo md = umapL go
           ConstField {} -> mkTypeField'
           ConstString {} -> mkTypeString'
           ConstUInt8 {} -> mkTypeUInt8'
+          ConstByteArray {} -> mkDynamic'
       NApp {} ->
         let (fn, args) = unfoldApps' node
             fty = Info.getNodeType fn
@@ -85,6 +86,8 @@ computeNodeTypeInfo md = umapL go
             _ -> error "incorrect random_ec_point builtin application"
           OpUInt8ToInt -> mkTypeInteger'
           OpUInt8FromInt -> mkTypeUInt8'
+          OpByteArrayFromListByte -> mkDynamic'
+          OpByteArrayLength -> mkTypeInteger'
       NCtr Constr {..} ->
         let ci = lookupConstructorInfo md _constrTag
             ii = lookupInductiveInfo md (ci ^. constructorInductive)
diff --git a/src/Juvix/Compiler/Core/Transformation/ConvertBuiltinTypes.hs b/src/Juvix/Compiler/Core/Transformation/ConvertBuiltinTypes.hs
index 5746972dd2..700f5ab357 100644
--- a/src/Juvix/Compiler/Core/Transformation/ConvertBuiltinTypes.hs
+++ b/src/Juvix/Compiler/Core/Transformation/ConvertBuiltinTypes.hs
@@ -20,6 +20,7 @@ convertNode md = umap go
           Just (BuiltinTypeAxiom BuiltinString) -> mkTypeString'
           Just (BuiltinTypeAxiom BuiltinField) -> mkTypeField'
           Just (BuiltinTypeAxiom BuiltinByte) -> mkTypeUInt8'
+          Just (BuiltinTypeAxiom BuiltinByteArray) -> mkTypeByteArray'
           _ -> node
         where
           ii = lookupInductiveInfo md _typeConstrSymbol
diff --git a/src/Juvix/Compiler/Core/Translation/FromInternal.hs b/src/Juvix/Compiler/Core/Translation/FromInternal.hs
index 6551eb4b7d..deb2eb6134 100644
--- a/src/Juvix/Compiler/Core/Translation/FromInternal.hs
+++ b/src/Juvix/Compiler/Core/Translation/FromInternal.hs
@@ -618,6 +618,9 @@ goAxiomInductive a = whenJust (a ^. Internal.axiomBuiltin) builtinInductive
       Internal.BuiltinByteEq -> return ()
       Internal.BuiltinByteToNat -> return ()
       Internal.BuiltinByteFromNat -> return ()
+      Internal.BuiltinByteArray -> registerInductiveAxiom (Just BuiltinByteArray) []
+      Internal.BuiltinByteArrayFromListByte -> return ()
+      Internal.BuiltinByteArrayLength -> return ()
 
     registerInductiveAxiom :: Maybe BuiltinAxiom -> [(Tag, Text, Type -> Type, Maybe BuiltinConstructor)] -> Sem r ()
     registerInductiveAxiom ax ctrs = do
@@ -826,6 +829,11 @@ goAxiomDef a = maybe goAxiomNotBuiltin builtinBody (a ^. Internal.axiomBuiltin)
         registerAxiomDef (mkLambda' mkTypeUInt8' (mkBuiltinApp' OpUInt8ToInt [mkVar' 0]))
       Internal.BuiltinByteFromNat ->
         registerAxiomDef (mkLambda' mkTypeInteger' (mkBuiltinApp' OpUInt8FromInt [mkVar' 0]))
+      Internal.BuiltinByteArray -> return ()
+      Internal.BuiltinByteArrayFromListByte ->
+        registerAxiomDef (mkLambda' mkDynamic' (mkBuiltinApp' OpByteArrayFromListByte [mkVar' 0]))
+      Internal.BuiltinByteArrayLength ->
+        registerAxiomDef (mkLambda' mkTypeInteger' (mkBuiltinApp' OpByteArrayLength [mkVar' 0]))
 
     axiomType' :: Sem r Type
     axiomType' = fromTopIndex (goType (a ^. Internal.axiomType))
@@ -1227,6 +1235,9 @@ goApplication a = do
         Just Internal.BuiltinByteEq -> app
         Just Internal.BuiltinByteToNat -> app
         Just Internal.BuiltinByteFromNat -> app
+        Just Internal.BuiltinByteArray -> app
+        Just Internal.BuiltinByteArrayFromListByte -> app
+        Just Internal.BuiltinByteArrayLength -> app
         Nothing -> app
     Internal.ExpressionIden (Internal.IdenFunction n) -> do
       funInfoBuiltin <- Internal.getFunctionBuiltinInfo n
diff --git a/src/Juvix/Compiler/Core/Translation/FromSource.hs b/src/Juvix/Compiler/Core/Translation/FromSource.hs
index 2592087272..26c8633064 100644
--- a/src/Juvix/Compiler/Core/Translation/FromSource.hs
+++ b/src/Juvix/Compiler/Core/Translation/FromSource.hs
@@ -79,6 +79,7 @@ parseToplevel = do
   lift declareBoolBuiltins
   lift declareNatBuiltins
   lift declareMaybeBuiltins
+  lift declareListBuiltins
   space
   P.endBy statement (kw delimSemicolon)
   r <- optional expression
@@ -580,6 +581,8 @@ builtinAppExpr varsNum vars = do
       <|> (kw kwAnomaVerifyWithMessage $> OpAnomaVerifyWithMessage)
       <|> (kw kwAnomaSignDetached $> OpAnomaSignDetached)
       <|> (kw kwAnomaVerifyDetached $> OpAnomaVerifyDetached)
+      <|> (kw kwByteArrayFromListByte $> OpByteArrayFromListByte)
+      <|> (kw kwByteArrayLength $> OpByteArrayLength)
   args <- P.many (atom varsNum vars)
   return $ mkBuiltinApp' op args
 
@@ -1119,6 +1122,8 @@ exprNamed varsNum vars = do
     "Int" -> return mkTypeInteger'
     "Field" -> return mkTypeField'
     "String" -> return mkTypeString'
+    "UInt8" -> return mkTypeUInt8'
+    "ByteArray" -> return mkDynamic'
     _ ->
       case HashMap.lookup txt vars of
         Just k -> do
diff --git a/src/Juvix/Compiler/Core/Translation/Stripped/FromCore.hs b/src/Juvix/Compiler/Core/Translation/Stripped/FromCore.hs
index 34c051b24e..2dd8bea953 100644
--- a/src/Juvix/Compiler/Core/Translation/Stripped/FromCore.hs
+++ b/src/Juvix/Compiler/Core/Translation/Stripped/FromCore.hs
@@ -112,6 +112,9 @@ fromCore fsize tab =
         BuiltinByteEq -> False
         BuiltinByteToNat -> False
         BuiltinByteFromNat -> False
+        BuiltinByteArray -> False
+        BuiltinByteArrayFromListByte -> False
+        BuiltinByteArrayLength -> False
       BuiltinTypeInductive i -> case i of
         BuiltinList -> True
         BuiltinMaybe -> True
diff --git a/src/Juvix/Compiler/Internal/Translation/FromConcrete.hs b/src/Juvix/Compiler/Internal/Translation/FromConcrete.hs
index 677ec97b02..295661c405 100644
--- a/src/Juvix/Compiler/Internal/Translation/FromConcrete.hs
+++ b/src/Juvix/Compiler/Internal/Translation/FromConcrete.hs
@@ -591,6 +591,9 @@ registerBuiltinAxiom d = \case
   BuiltinByteEq -> registerByteEq d
   BuiltinByteToNat -> registerByteToNat d
   BuiltinByteFromNat -> registerByteFromNat d
+  BuiltinByteArray -> registerByteArray d
+  BuiltinByteArrayFromListByte -> registerByteArrayFromListByte d
+  BuiltinByteArrayLength -> registerByteArrayLength d
 
 goInductive ::
   (Members '[Reader EntryPoint, Reader DefaultArgsStack, NameIdGen, Reader Pragmas, Builtins, Error ScoperError, State ConstructorInfos, Reader S.InfoTable] r) =>
diff --git a/src/Juvix/Compiler/Nockma/Evaluator.hs b/src/Juvix/Compiler/Nockma/Evaluator.hs
index 8ee092432e..a8ef610607 100644
--- a/src/Juvix/Compiler/Nockma/Evaluator.hs
+++ b/src/Juvix/Compiler/Nockma/Evaluator.hs
@@ -7,6 +7,7 @@ module Juvix.Compiler.Nockma.Evaluator
 where
 
 import Crypto.Sign.Ed25519
+import Data.ByteString qualified as BS
 import Data.HashMap.Strict qualified as HashMap
 import Juvix.Compiler.Nockma.Encoding
 import Juvix.Compiler.Nockma.Encoding qualified as Encoding
@@ -253,10 +254,36 @@ evalProfile inistack initerm =
             StdlibCatBytes -> case args' of
               TCell (TermAtom arg1) (TermAtom arg2) -> goCat arg1 arg2
               _ -> error "expected a term with two atoms"
+            StdlibFoldBytes -> TermAtom <$> goFoldBytes args'
+            StdlibLengthList -> do
+              let xs = checkTermToList args'
+              let len = integerToNatural (toInteger (length xs))
+              TermAtom . mkEmptyAtom <$> fromNatural len
           where
             goCat :: Atom a -> Atom a -> Sem r (Term a)
             goCat arg1 arg2 = TermAtom . setAtomHint AtomHintString <$> atomConcatenateBytes arg1 arg2
 
+            goFoldBytes :: Term a -> Sem r (Atom a)
+            goFoldBytes c = do
+              bs <- mapM nockNatural (checkTermToListAtom c)
+              byteStringToAtom (BS.pack (fromIntegral <$> bs))
+
+            checkTermToList :: Term a -> [Term a]
+            checkTermToList = \case
+              TermAtom x ->
+                if
+                    | x `nockmaEq` nockNil -> []
+                    | otherwise -> error "expected a list to be terminated by nil"
+              TermCell c -> c ^. cellLeft : checkTermToList (c ^. cellRight)
+
+            checkTermToListAtom :: Term a -> [Atom a]
+            checkTermToListAtom = map check . checkTermToList
+              where
+                check :: Term a -> Atom a
+                check = \case
+                  TermAtom x -> x
+                  TermCell {} -> error "expect list element to be an atom"
+
             signatureLength :: Int
             signatureLength = 64
 
diff --git a/src/Juvix/Compiler/Nockma/StdlibFunction.hs b/src/Juvix/Compiler/Nockma/StdlibFunction.hs
index fb3ac49fb0..4bb1c144ce 100644
--- a/src/Juvix/Compiler/Nockma/StdlibFunction.hs
+++ b/src/Juvix/Compiler/Nockma/StdlibFunction.hs
@@ -26,6 +26,7 @@ stdlibPath = \case
   StdlibSign -> [nock| [9 10 0 1] |]
   StdlibSignDetached -> [nock| [9 23 0 1] |]
   StdlibVerify -> [nock| [9 4 0 1] |]
+  StdlibLengthList -> [nock| [9 1.406 0 31] |]
   -- Obtained from the urbit dojo using:
   --
   -- =>  anoma  !=(~(cat block 3))
@@ -33,3 +34,44 @@ stdlibPath = \case
   -- The `3` here is because we want to treat each atom as sequences of 2^3
   -- bits, i.e bytes.
   StdlibCatBytes -> [nock| [8 [9 10 0 7] 9 4 10 [6 7 [0 3] 1 3] 0 2] |]
+  -- Obtained from the urbit dojo using:
+  --
+  -- =>(anoma !=(|=([l=(list @)] (foldr l |=([fst=@ snd=@] (add (~(lsh block 3) 1 snd) fst))))))
+  --
+  -- The `3` here is because we want to shift left in byte = 2^3 bit steps.
+  StdlibFoldBytes ->
+    [nock|
+            [ 8
+              [1 0]
+              [ 1
+                8
+                [9 46 0 127]
+                9
+                2
+                10
+                [ 6
+                  [0 14]
+                  7
+                  [0 3]
+                  8
+                  [1 0 0]
+                  [ 1
+                    8
+                    [9 20 0 1.023]
+                    9
+                    2
+                    10
+                    [6 [7 [0 3] 8 [8 [9 10 0 127] 9 90 10 [6 7 [0 3] 1 3] 0 2] 9 2 10 [6 [7 [0 3] 1 1] 0 29] 0 2] 0 28]
+                    0
+                    2
+                  ]
+                  0
+                  1
+                ]
+                0
+                2
+              ]
+              0
+              1
+            ]
+     |]
diff --git a/src/Juvix/Compiler/Nockma/StdlibFunction/Base.hs b/src/Juvix/Compiler/Nockma/StdlibFunction/Base.hs
index 38dbc34ba9..de96d7c997 100644
--- a/src/Juvix/Compiler/Nockma/StdlibFunction/Base.hs
+++ b/src/Juvix/Compiler/Nockma/StdlibFunction/Base.hs
@@ -21,6 +21,8 @@ instance Pretty StdlibFunction where
     StdlibSignDetached -> "sign-detached"
     StdlibVerify -> "verify"
     StdlibCatBytes -> "cat"
+    StdlibFoldBytes -> "fold-bytes"
+    StdlibLengthList -> "length-list"
 
 data StdlibFunction
   = StdlibDec
@@ -39,6 +41,8 @@ data StdlibFunction
   | StdlibSignDetached
   | StdlibVerify
   | StdlibCatBytes
+  | StdlibFoldBytes
+  | StdlibLengthList
   deriving stock (Show, Lift, Eq, Bounded, Enum, Generic)
 
 instance Hashable StdlibFunction
diff --git a/src/Juvix/Compiler/Nockma/Translation/FromTree.hs b/src/Juvix/Compiler/Nockma/Translation/FromTree.hs
index e8c7d8639a..9b733f0a32 100644
--- a/src/Juvix/Compiler/Nockma/Translation/FromTree.hs
+++ b/src/Juvix/Compiler/Nockma/Translation/FromTree.hs
@@ -33,6 +33,7 @@ module Juvix.Compiler.Nockma.Translation.FromTree
   )
 where
 
+import Data.ByteString qualified as BS
 import Juvix.Compiler.Nockma.Encoding
 import Juvix.Compiler.Nockma.Language.Path
 import Juvix.Compiler.Nockma.Pretty
@@ -360,6 +361,7 @@ compile :: forall r. (Members '[Reader FunctionCtx, Reader CompilerCtx] r) => Tr
 compile = \case
   Tree.Binop b -> goBinop b
   Tree.Unop b -> goUnop b
+  Tree.ByteArray b -> goByteArrayOp b
   Tree.Cairo {} -> cairoErr
   Tree.Anoma b -> goAnomaOp b
   Tree.Constant c -> return (goConstant (c ^. Tree.nodeConstant))
@@ -441,6 +443,7 @@ compile = \case
       Tree.ConstVoid -> OpQuote # constVoid
       Tree.ConstField {} -> fieldErr
       Tree.ConstUInt8 i -> nockIntegralLiteral i
+      Tree.ConstByteArray bs -> OpQuote # (toNock @Natural (fromIntegral (BS.length bs)) # toNock (byteStringToNatural bs))
 
     goConstString :: Text -> Term Natural
     goConstString t =
@@ -492,6 +495,18 @@ compile = \case
         Tree.OpAnomaVerifyWithMessage -> return (goAnomaVerifyWithMessage args)
         Tree.OpAnomaSignDetached -> return (goAnomaSignDetached args)
 
+    goByteArrayOp :: Tree.NodeByteArray -> Sem r (Term Natural)
+    goByteArrayOp Tree.NodeByteArray {..} = do
+      args <- mapM compile _nodeByteArrayArgs
+      return $ case _nodeByteArrayOpcode of
+        Tree.OpByteArrayLength -> goByteArrayLength args
+        Tree.OpByteArrayFromListUInt8 -> callStdlib StdlibLengthList args # callStdlib StdlibFoldBytes args
+      where
+        goByteArrayLength :: [Term Natural] -> Term Natural
+        goByteArrayLength = \case
+          [ba] -> ba >># opAddress "head-of-the-bytestring" [L]
+          _ -> impossible
+
     goUnop :: Tree.NodeUnop -> Sem r (Term Natural)
     goUnop Tree.NodeUnop {..} = do
       arg <- compile _nodeUnopArg
diff --git a/src/Juvix/Compiler/Tree/Data/TransformationId.hs b/src/Juvix/Compiler/Tree/Data/TransformationId.hs
index 6b0b5d25ac..8238814ae3 100644
--- a/src/Juvix/Compiler/Tree/Data/TransformationId.hs
+++ b/src/Juvix/Compiler/Tree/Data/TransformationId.hs
@@ -13,6 +13,7 @@ data TransformationId
   | FilterUnreachable
   | Validate
   | CheckNoAnoma
+  | CheckNoByteArray
   deriving stock (Data, Bounded, Enum, Show)
 
 data PipelineId
@@ -27,7 +28,7 @@ toNockmaTransformations :: [TransformationId]
 toNockmaTransformations = [Validate, Apply, FilterUnreachable, TempHeight]
 
 toAsmTransformations :: [TransformationId]
-toAsmTransformations = [Validate, CheckNoAnoma]
+toAsmTransformations = [Validate, CheckNoAnoma, CheckNoByteArray]
 
 toCairoAsmTransformations :: [TransformationId]
 toCairoAsmTransformations = [Validate, Apply, FilterUnreachable]
@@ -43,6 +44,7 @@ instance TransformationId' TransformationId where
     FilterUnreachable -> strFilterUnreachable
     Validate -> strValidate
     CheckNoAnoma -> strCheckNoAnoma
+    CheckNoByteArray -> strCheckNoByteArray
 
 instance PipelineId' TransformationId PipelineId where
   pipelineText :: PipelineId -> Text
diff --git a/src/Juvix/Compiler/Tree/Data/TransformationId/Strings.hs b/src/Juvix/Compiler/Tree/Data/TransformationId/Strings.hs
index ababa4da2f..54c9584530 100644
--- a/src/Juvix/Compiler/Tree/Data/TransformationId/Strings.hs
+++ b/src/Juvix/Compiler/Tree/Data/TransformationId/Strings.hs
@@ -34,3 +34,6 @@ strValidate = "validate"
 
 strCheckNoAnoma :: Text
 strCheckNoAnoma = "check-no-anoma"
+
+strCheckNoByteArray :: Text
+strCheckNoByteArray = "check-no-bytearray"
diff --git a/src/Juvix/Compiler/Tree/Evaluator.hs b/src/Juvix/Compiler/Tree/Evaluator.hs
index c3c79b2ddf..53f13f1f12 100644
--- a/src/Juvix/Compiler/Tree/Evaluator.hs
+++ b/src/Juvix/Compiler/Tree/Evaluator.hs
@@ -1,6 +1,7 @@
 module Juvix.Compiler.Tree.Evaluator where
 
 import Control.Exception qualified as Exception
+import Data.ByteString qualified as BS
 import GHC.IO (unsafePerformIO)
 import GHC.Show qualified as S
 import Juvix.Compiler.Core.Data.BinderList qualified as BL
@@ -37,6 +38,7 @@ hEval hout tab = eval' [] mempty
     eval' args temps node = case node of
       Binop x -> goBinop x
       Unop x -> goUnop x
+      ByteArray x -> goByteArrayOp x
       Anoma {} -> evalError "unsupported: Anoma builtin"
       Cairo {} -> evalError "unsupported: Cairo builtin"
       Constant c -> goConstant c
@@ -76,6 +78,33 @@ hEval hout tab = eval' [] mempty
                 OpTrace -> goTrace v
                 OpFail -> goFail v
 
+        goByteArrayOp :: NodeByteArray -> Value
+        goByteArrayOp NodeByteArray {..} =
+          case _nodeByteArrayOpcode of
+            OpByteArrayLength -> case _nodeByteArrayArgs of
+              [nodeArg] ->
+                let !arg = eval' args temps nodeArg
+                 in case arg of
+                      (ValByteArray bs) -> ValInteger (fromIntegral (BS.length bs))
+                      _ -> evalError "expected argument to be a ByteString"
+              _ -> evalError "expected exactly one argument"
+            OpByteArrayFromListUInt8 -> case _nodeByteArrayArgs of
+              [nodeArg] ->
+                let !arg = eval' args temps nodeArg
+                    !listUInt8 :: [Word8] = checkListUInt8 arg
+                 in ValByteArray (BS.pack listUInt8)
+              _ -> evalError "expected exactly one argument"
+              where
+                checkListUInt8 :: Value -> [Word8]
+                checkListUInt8 = \case
+                  ValConstr c -> case c ^. constrArgs of
+                    -- is nil
+                    [] -> []
+                    -- is cons
+                    [ValUInt8 w, t] -> w : checkListUInt8 t
+                    _ -> evalError "expected either a nullary or a binary constructor"
+                  _ -> evalError "expected a constructor"
+
         goFail :: Value -> Value
         goFail v = evalError ("failure: " <> printValue tab v)
 
@@ -232,6 +261,7 @@ valueToNode = \case
           _nodeAllocClosureArgs = map valueToNode _closureArgs
         }
   ValUInt8 i -> mkConst $ ConstUInt8 i
+  ValByteArray b -> mkConst $ ConstByteArray b
 
 hEvalIO :: (MonadIO m) => Handle -> Handle -> InfoTable -> FunctionInfo -> m Value
 hEvalIO hin hout infoTable funInfo = do
diff --git a/src/Juvix/Compiler/Tree/Evaluator/Builtins.hs b/src/Juvix/Compiler/Tree/Evaluator/Builtins.hs
index 58b8e53772..d9c1fda4f9 100644
--- a/src/Juvix/Compiler/Tree/Evaluator/Builtins.hs
+++ b/src/Juvix/Compiler/Tree/Evaluator/Builtins.hs
@@ -130,6 +130,7 @@ constantToValue = \case
   ConstUnit -> ValUnit
   ConstVoid -> ValVoid
   ConstUInt8 i -> ValUInt8 i
+  ConstByteArray b -> ValByteArray b
 
 valueToConstant :: Value -> Constant
 valueToConstant = \case
diff --git a/src/Juvix/Compiler/Tree/EvaluatorEff.hs b/src/Juvix/Compiler/Tree/EvaluatorEff.hs
index 2acca9d3e4..8ecbbc9782 100644
--- a/src/Juvix/Compiler/Tree/EvaluatorEff.hs
+++ b/src/Juvix/Compiler/Tree/EvaluatorEff.hs
@@ -1,6 +1,7 @@
 module Juvix.Compiler.Tree.EvaluatorEff (eval, hEvalIOEither) where
 
 import Control.Exception qualified as Exception
+import Data.ByteString qualified as BS
 import Juvix.Compiler.Core.Data.BinderList qualified as BL
 import Juvix.Compiler.Tree.Data.InfoTable
 import Juvix.Compiler.Tree.Error
@@ -33,6 +34,7 @@ eval tab = runReader emptyEvalCtx . eval'
     eval' node = case node of
       Binop x -> goBinop x
       Unop x -> goUnop x
+      ByteArray x -> goByteArrayOp x
       Anoma {} -> evalError "unsupported: Anoma builtins"
       Cairo {} -> evalError "unsupported: Cairo builtins"
       Constant c -> return (goConstant c)
@@ -71,6 +73,33 @@ eval tab = runReader emptyEvalCtx . eval'
             OpTrace -> goTrace v
             OpFail -> goFail v
 
+        goByteArrayOp :: NodeByteArray -> Sem r' Value
+        goByteArrayOp NodeByteArray {..} =
+          case _nodeByteArrayOpcode of
+            OpByteArrayLength -> case _nodeByteArrayArgs of
+              [nodeArg] -> do
+                arg <- eval' nodeArg
+                case arg of
+                  (ValByteArray bs) -> return $ ValInteger (fromIntegral (BS.length bs))
+                  _ -> evalError "expected argument to be a ByteString"
+              _ -> evalError "expected exactly one argument"
+            OpByteArrayFromListUInt8 -> case _nodeByteArrayArgs of
+              [nodeArg] -> do
+                arg <- eval' nodeArg
+                listUInt8 :: [Word8] <- checkListUInt8 arg
+                return $ ValByteArray (BS.pack listUInt8)
+              _ -> evalError "expected exactly one argument"
+              where
+                checkListUInt8 :: Value -> Sem r' [Word8]
+                checkListUInt8 = \case
+                  ValConstr c -> case c ^. constrArgs of
+                    -- is nil
+                    [] -> return []
+                    -- is cons
+                    [ValUInt8 w, t] -> (w :) <$> checkListUInt8 t
+                    _ -> evalError "expected either a nullary or a binary constructor"
+                  _ -> evalError "expected a constructor"
+
         goFail :: Value -> Sem r' Value
         goFail v = evalError ("failure: " <> printValue tab v)
 
diff --git a/src/Juvix/Compiler/Tree/Extra/Base.hs b/src/Juvix/Compiler/Tree/Extra/Base.hs
index 38b676670f..a2c15021ab 100644
--- a/src/Juvix/Compiler/Tree/Extra/Base.hs
+++ b/src/Juvix/Compiler/Tree/Extra/Base.hs
@@ -18,6 +18,7 @@ getNodeInfo :: Node -> NodeInfo
 getNodeInfo = \case
   Binop NodeBinop {..} -> _nodeBinopInfo
   Unop NodeUnop {..} -> _nodeUnopInfo
+  ByteArray NodeByteArray {..} -> _nodeByteArrayInfo
   Cairo NodeCairo {..} -> _nodeCairoInfo
   Anoma NodeAnoma {..} -> _nodeAnomaInfo
   Constant NodeConstant {..} -> _nodeConstantInfo
@@ -142,6 +143,17 @@ destruct = \case
                 _nodeUnopInfo
               }
       }
+  ByteArray NodeByteArray {..} ->
+    NodeDetails
+      { _nodeChildren = map noTempVar _nodeByteArrayArgs,
+        _nodeReassemble = manyChildren $ \args ->
+          ByteArray
+            NodeByteArray
+              { _nodeByteArrayArgs = args,
+                _nodeByteArrayOpcode,
+                _nodeByteArrayInfo
+              }
+      }
   Cairo NodeCairo {..} ->
     NodeDetails
       { _nodeChildren = map noTempVar _nodeCairoArgs,
diff --git a/src/Juvix/Compiler/Tree/Extra/Type.hs b/src/Juvix/Compiler/Tree/Extra/Type.hs
index 1dfc32409a..1903309a10 100644
--- a/src/Juvix/Compiler/Tree/Extra/Type.hs
+++ b/src/Juvix/Compiler/Tree/Extra/Type.hs
@@ -4,33 +4,18 @@
 {-# HLINT ignore "Avoid restricted extensions" #-}
 {-# HLINT ignore "Avoid restricted flags" #-}
 
-module Juvix.Compiler.Tree.Extra.Type where
+module Juvix.Compiler.Tree.Extra.Type
+  ( module Juvix.Compiler.Tree.Extra.Type,
+    module Juvix.Compiler.Tree.Extra.Type.Base,
+  )
+where
 
 import Juvix.Compiler.Tree.Data.InfoTable.Base
 import Juvix.Compiler.Tree.Error
+import Juvix.Compiler.Tree.Extra.Type.Base
 import Juvix.Compiler.Tree.Language.Base
 import Juvix.Compiler.Tree.Pretty
 
-mkTypeInteger :: Type
-mkTypeInteger = TyInteger (TypeInteger Nothing Nothing)
-
-mkTypeUInt8 :: Type
-mkTypeUInt8 = TyInteger (TypeInteger (Just 0) (Just 255))
-
-mkTypeBool :: Type
-mkTypeBool = TyBool (TypeBool (BuiltinTag TagTrue) (BuiltinTag TagFalse))
-
-mkTypeConstr :: Symbol -> Tag -> [Type] -> Type
-mkTypeConstr ind tag argTypes = TyConstr (TypeConstr ind tag argTypes)
-
-mkTypeInductive :: Symbol -> Type
-mkTypeInductive ind = TyInductive (TypeInductive ind)
-
-mkTypeFun :: [Type] -> Type -> Type
-mkTypeFun args tgt = case args of
-  [] -> tgt
-  a : args' -> TyFun (TypeFun (a :| args') tgt)
-
 unfoldType :: Type -> ([Type], Type)
 unfoldType ty = (typeArgs ty, typeTarget ty)
 
@@ -80,6 +65,7 @@ isSubtype ty1 ty2 = case (ty1, ty2) of
   (TyBool {}, TyBool {}) -> True
   (TyString, TyString) -> True
   (TyField, TyField) -> True
+  (TyByteArray, TyByteArray) -> True
   (TyUnit, TyUnit) -> True
   (TyVoid, TyVoid) -> True
   (TyInductive {}, TyInductive {}) -> ty1 == ty2
@@ -93,6 +79,8 @@ isSubtype ty1 ty2 = case (ty1, ty2) of
   (_, TyString) -> False
   (TyField, _) -> False
   (_, TyField) -> False
+  (TyByteArray, _) -> False
+  (_, TyByteArray) -> False
   (TyBool {}, _) -> False
   (_, TyBool {}) -> False
   (TyFun {}, _) -> False
@@ -149,6 +137,7 @@ unifyTypes ty1 ty2 = case (ty1, ty2) of
     | ty1 == ty2 -> return ty1
   (TyString, TyString) -> return TyString
   (TyField, TyField) -> return TyField
+  (TyByteArray, TyByteArray) -> return TyByteArray
   (TyUnit, TyUnit) -> return TyUnit
   (TyVoid, TyVoid) -> return TyVoid
   (TyInductive {}, TyInductive {})
@@ -163,6 +152,8 @@ unifyTypes ty1 ty2 = case (ty1, ty2) of
   (_, TyString) -> err
   (TyField, _) -> err
   (_, TyField) -> err
+  (TyByteArray, _) -> err
+  (_, TyByteArray) -> err
   (TyBool {}, _) -> err
   (_, TyBool {}) -> err
   (TyFun {}, _) -> err
diff --git a/src/Juvix/Compiler/Tree/Extra/Type/Base.hs b/src/Juvix/Compiler/Tree/Extra/Type/Base.hs
new file mode 100644
index 0000000000..6858a2385a
--- /dev/null
+++ b/src/Juvix/Compiler/Tree/Extra/Type/Base.hs
@@ -0,0 +1,24 @@
+module Juvix.Compiler.Tree.Extra.Type.Base where
+
+import Juvix.Compiler.Tree.Language.Base
+import Juvix.Compiler.Tree.Language.Type
+
+mkTypeInteger :: Type
+mkTypeInteger = TyInteger (TypeInteger Nothing Nothing)
+
+mkTypeUInt8 :: Type
+mkTypeUInt8 = TyInteger (TypeInteger (Just 0) (Just 255))
+
+mkTypeBool :: Type
+mkTypeBool = TyBool (TypeBool (BuiltinTag TagTrue) (BuiltinTag TagFalse))
+
+mkTypeConstr :: Symbol -> Tag -> [Type] -> Type
+mkTypeConstr ind tag argTypes = TyConstr (TypeConstr ind tag argTypes)
+
+mkTypeInductive :: Symbol -> Type
+mkTypeInductive ind = TyInductive (TypeInductive ind)
+
+mkTypeFun :: [Type] -> Type -> Type
+mkTypeFun args tgt = case args of
+  [] -> tgt
+  a : args' -> TyFun (TypeFun (a :| args') tgt)
diff --git a/src/Juvix/Compiler/Tree/Keywords.hs b/src/Juvix/Compiler/Tree/Keywords.hs
index b878fb50c1..989cdb9137 100644
--- a/src/Juvix/Compiler/Tree/Keywords.hs
+++ b/src/Juvix/Compiler/Tree/Keywords.hs
@@ -19,6 +19,8 @@ import Juvix.Data.Keyword.All
     kwArgsNum,
     kwAtoi,
     kwBr,
+    kwByteArrayFromListUInt8,
+    kwByteArrayLength,
     kwCAlloc,
     kwCCall,
     kwCExtend,
@@ -88,5 +90,7 @@ allKeywords =
          kwAnomaVerifyWithMessage,
          kwPoseidon,
          kwEcOp,
-         kwRandomEcPoint
+         kwRandomEcPoint,
+         kwByteArrayLength,
+         kwByteArrayFromListUInt8
        ]
diff --git a/src/Juvix/Compiler/Tree/Language.hs b/src/Juvix/Compiler/Tree/Language.hs
index d4242f74f2..bbb9614910 100644
--- a/src/Juvix/Compiler/Tree/Language.hs
+++ b/src/Juvix/Compiler/Tree/Language.hs
@@ -18,6 +18,7 @@ data Node
   | Unop NodeUnop
   | Cairo NodeCairo
   | Anoma NodeAnoma
+  | ByteArray NodeByteArray
   | -- | A constant value.
     Constant NodeConstant
   | -- | A memory reference.
@@ -82,6 +83,12 @@ data NodeUnop = NodeUnop
     _nodeUnopArg :: Node
   }
 
+data NodeByteArray = NodeByteArray
+  { _nodeByteArrayInfo :: NodeInfo,
+    _nodeByteArrayOpcode :: ByteArrayOp,
+    _nodeByteArrayArgs :: [Node]
+  }
+
 data NodeCairo = NodeCairo
   { _nodeCairoInfo :: NodeInfo,
     _nodeCairoOpcode :: CairoOp,
diff --git a/src/Juvix/Compiler/Tree/Language/Base.hs b/src/Juvix/Compiler/Tree/Language/Base.hs
index 99208bd703..10d9f9f52a 100644
--- a/src/Juvix/Compiler/Tree/Language/Base.hs
+++ b/src/Juvix/Compiler/Tree/Language/Base.hs
@@ -19,6 +19,7 @@ data Constant
   | ConstUnit
   | ConstVoid
   | ConstUInt8 Word8
+  | ConstByteArray ByteString
   deriving stock (Eq, Generic)
 
 instance (Hashable Constant)
diff --git a/src/Juvix/Compiler/Tree/Language/Builtins.hs b/src/Juvix/Compiler/Tree/Language/Builtins.hs
index 94b04cfa2a..3145026a2a 100644
--- a/src/Juvix/Compiler/Tree/Language/Builtins.hs
+++ b/src/Juvix/Compiler/Tree/Language/Builtins.hs
@@ -66,6 +66,14 @@ data CairoOp
     OpCairoRandomEcPoint
   deriving stock (Eq)
 
+-- | Builtin ByteArray operations
+data ByteArrayOp
+  = -- | Convert a list of UInt8 to a ByteArray
+    OpByteArrayFromListUInt8
+  | -- | Get the size of a ByteArray
+    OpByteArrayLength
+  deriving stock (Eq)
+
 cairoOpArgsNum :: CairoOp -> Int
 cairoOpArgsNum = \case
   OpCairoPoseidon -> 1
diff --git a/src/Juvix/Compiler/Tree/Language/Type.hs b/src/Juvix/Compiler/Tree/Language/Type.hs
index 358dd3c265..517576e1d0 100644
--- a/src/Juvix/Compiler/Tree/Language/Type.hs
+++ b/src/Juvix/Compiler/Tree/Language/Type.hs
@@ -8,6 +8,7 @@ data Type
   | TyBool TypeBool
   | TyString
   | TyField
+  | TyByteArray
   | TyUnit
   | TyVoid
   | TyInductive TypeInductive
@@ -81,6 +82,7 @@ instance HasAtomicity Type where
     TyField -> Atom
     TyUnit -> Atom
     TyVoid -> Atom
+    TyByteArray -> Atom
     TyInductive x -> atomicity x
     TyConstr x -> atomicity x
     TyFun x -> atomicity x
diff --git a/src/Juvix/Compiler/Tree/Language/Value.hs b/src/Juvix/Compiler/Tree/Language/Value.hs
index 2e4387a6f0..7df0ef8424 100644
--- a/src/Juvix/Compiler/Tree/Language/Value.hs
+++ b/src/Juvix/Compiler/Tree/Language/Value.hs
@@ -24,6 +24,7 @@ data Value
   | ValConstr Constr
   | ValClosure Closure
   | ValUInt8 Word8
+  | ValByteArray ByteString
   deriving stock (Eq)
 
 data Constr = Constr
@@ -62,3 +63,4 @@ instance HasAtomicity Value where
     ValConstr c -> atomicity c
     ValClosure cl -> atomicity cl
     ValUInt8 {} -> Atom
+    ValByteArray {} -> Atom
diff --git a/src/Juvix/Compiler/Tree/Pretty/Base.hs b/src/Juvix/Compiler/Tree/Pretty/Base.hs
index bf5e665d0e..abdec2bd81 100644
--- a/src/Juvix/Compiler/Tree/Pretty/Base.hs
+++ b/src/Juvix/Compiler/Tree/Pretty/Base.hs
@@ -4,12 +4,14 @@ module Juvix.Compiler.Tree.Pretty.Base
   )
 where
 
+import Data.ByteString qualified as BS
 import Data.Foldable
 import Data.HashMap.Strict qualified as HashMap
 import Data.List.NonEmpty qualified as NonEmpty
 import Juvix.Compiler.Core.Pretty.Base qualified as Core
 import Juvix.Compiler.Internal.Data.Name
 import Juvix.Compiler.Tree.Data.InfoTable
+import Juvix.Compiler.Tree.Extra.Type.Base
 import Juvix.Compiler.Tree.Language
 import Juvix.Compiler.Tree.Language.Value
 import Juvix.Compiler.Tree.Pretty.Extra
@@ -101,6 +103,7 @@ instance PrettyCode Value where
       ppCode cl
     ValUInt8 i ->
       return $ integer i
+    ValByteArray bs -> ppCode bs
 
 instance PrettyCode TypeInductive where
   ppCode :: (Member (Reader Options) r) => TypeInductive -> Sem r (Doc Ann)
@@ -139,10 +142,14 @@ instance PrettyCode Type where
   ppCode = \case
     TyDynamic ->
       return $ annotate (AnnKind KNameInductive) Str.mul
-    TyInteger {} ->
-      return $ annotate (AnnKind KNameInductive) Str.integer
+    t@(TyInteger {})
+      | t == mkTypeUInt8 ->
+          return $ annotate (AnnKind KNameInductive) Str.uint8
+    TyInteger {} -> return $ annotate (AnnKind KNameInductive) Str.integer
     TyField {} ->
       return $ annotate (AnnKind KNameInductive) Str.field
+    TyByteArray {} ->
+      return $ annotate (AnnKind KNameInductive) Str.byteArray
     TyBool {} ->
       return $ annotate (AnnKind KNameInductive) Str.bool
     TyString ->
@@ -200,7 +207,24 @@ instance PrettyCode Constant where
     ConstVoid {} ->
       return $ annotate (AnnKind KNameConstructor) Str.void
     ConstUInt8 v ->
-      return $ annotate AnnLiteralInteger (pretty v)
+      return $ annotate AnnLiteralInteger (pretty v <> "u8")
+    ConstByteArray v -> do
+      ctorOp <- ppCode OpByteArrayFromListUInt8
+      bs <- ppCode v
+      return (ctorOp <> parens bs)
+
+instance PrettyCode ByteString where
+  ppCode bs = do
+    ppBytes <- mapM ppCode (ConstUInt8 <$> BS.unpack bs)
+    return (toListCtors ppBytes)
+    where
+      toListCtors :: [Doc Ann] -> Doc Ann
+      toListCtors = \case
+        [] -> nodeAllocCtor Str.nil []
+        (x : xs) -> nodeAllocCtor Str.cons [x, toListCtors xs]
+
+      nodeAllocCtor :: Text -> [Doc Ann] -> Doc Ann
+      nodeAllocCtor n args = primitive Str.instrAlloc <> brackets (pretty n) <> parens (ppCodeArgs' args)
 
 instance PrettyCode BoolOp where
   ppCode op = return $ primitive $ case op of
@@ -246,6 +270,12 @@ instance PrettyCode UnaryOp where
     OpIntToUInt8 -> Str.instrIntToUInt8
     OpUInt8ToInt -> Str.instrUInt8ToInt
 
+instance PrettyCode ByteArrayOp where
+  ppCode =
+    return . \case
+      OpByteArrayFromListUInt8 -> Str.instrByteArrayFromListUInt8
+      OpByteArrayLength -> Str.instrByteArrayLength
+
 instance PrettyCode CairoOp where
   ppCode op = return $ primitive $ case op of
     OpCairoPoseidon -> Str.instrPoseidon
@@ -286,6 +316,12 @@ instance PrettyCode NodeAnoma where
     args <- ppCodeArgs _nodeAnomaArgs
     return (op <> parens args)
 
+instance PrettyCode NodeByteArray where
+  ppCode NodeByteArray {..} = do
+    op <- ppCode _nodeByteArrayOpcode
+    args <- ppCodeArgs _nodeByteArrayArgs
+    return (op <> parens args)
+
 instance PrettyCode NodeConstant where
   ppCode NodeConstant {..} = ppCode _nodeConstant
 
@@ -295,7 +331,10 @@ instance PrettyCode NodeMemRef where
 ppCodeArgs :: (Member (Reader Options) r) => [Node] -> Sem r (Doc Ann)
 ppCodeArgs args = do
   args' <- mapM ppCode args
-  return $ hsep $ punctuate comma args'
+  return $ ppCodeArgs' args'
+
+ppCodeArgs' :: [Doc Ann] -> Doc Ann
+ppCodeArgs' args = hsep $ punctuate comma args
 
 instance PrettyCode NodeAllocConstr where
   ppCode NodeAllocConstr {..} = do
@@ -378,6 +417,7 @@ instance PrettyCode Node where
   ppCode = \case
     Binop x -> ppCode x
     Unop x -> ppCode x
+    ByteArray x -> ppCode x
     Anoma x -> ppCode x
     Cairo x -> ppCode x
     Constant x -> ppCode x
diff --git a/src/Juvix/Compiler/Tree/Transformation.hs b/src/Juvix/Compiler/Tree/Transformation.hs
index e78c7ce17d..39120e5dd0 100644
--- a/src/Juvix/Compiler/Tree/Transformation.hs
+++ b/src/Juvix/Compiler/Tree/Transformation.hs
@@ -11,6 +11,7 @@ import Juvix.Compiler.Tree.Error
 import Juvix.Compiler.Tree.Transformation.Apply
 import Juvix.Compiler.Tree.Transformation.Base
 import Juvix.Compiler.Tree.Transformation.CheckNoAnoma
+import Juvix.Compiler.Tree.Transformation.CheckNoByteArray
 import Juvix.Compiler.Tree.Transformation.FilterUnreachable
 import Juvix.Compiler.Tree.Transformation.IdentityTrans
 import Juvix.Compiler.Tree.Transformation.TempHeight
@@ -29,3 +30,4 @@ applyTransformations ts tbl = foldM (flip appTrans) tbl ts
       FilterUnreachable -> return . filterUnreachable
       Validate -> mapError (JuvixError @TreeError) . validate
       CheckNoAnoma -> \tbl' -> mapError (JuvixError @TreeError) (checkNoAnoma tbl') $> tbl'
+      CheckNoByteArray -> \tbl' -> mapError (JuvixError @TreeError) (checkNoByteArray tbl') $> tbl'
diff --git a/src/Juvix/Compiler/Tree/Transformation/CheckNoByteArray.hs b/src/Juvix/Compiler/Tree/Transformation/CheckNoByteArray.hs
new file mode 100644
index 0000000000..2e2fd76a08
--- /dev/null
+++ b/src/Juvix/Compiler/Tree/Transformation/CheckNoByteArray.hs
@@ -0,0 +1,24 @@
+module Juvix.Compiler.Tree.Transformation.CheckNoByteArray where
+
+import Juvix.Compiler.Tree.Data.InfoTable
+import Juvix.Compiler.Tree.Error
+import Juvix.Compiler.Tree.Extra.Recursors
+import Juvix.Compiler.Tree.Transformation.Base
+
+checkNoByteArray :: forall r. (Member (Error TreeError) r) => InfoTable -> Sem r ()
+checkNoByteArray = walkT checkNode
+  where
+    checkNode :: Symbol -> Node -> Sem r ()
+    checkNode _ = \case
+      ByteArray NodeByteArray {..} -> case _nodeByteArrayOpcode of
+        OpByteArrayLength -> unsupportedErr "OpByteArrayLength"
+        OpByteArrayFromListUInt8 -> unsupportedErr "OpByteArrayFromListUInt8"
+        where
+          unsupportedErr :: Text -> Sem r ()
+          unsupportedErr opName =
+            throw
+              TreeError
+                { _treeErrorMsg = opName <> " is unsupported",
+                  _treeErrorLoc = _nodeByteArrayInfo ^. nodeInfoLocation
+                }
+      _ -> return ()
diff --git a/src/Juvix/Compiler/Tree/Transformation/Validate.hs b/src/Juvix/Compiler/Tree/Transformation/Validate.hs
index 2565c76982..c9ba84d41f 100644
--- a/src/Juvix/Compiler/Tree/Transformation/Validate.hs
+++ b/src/Juvix/Compiler/Tree/Transformation/Validate.hs
@@ -15,6 +15,7 @@ inferType tab funInfo = goInfer mempty
     goInfer bl = \case
       Binop x -> goBinop bl x
       Unop x -> goUnop bl x
+      ByteArray x -> goByteArray bl x
       Cairo x -> goCairo bl x
       Anoma x -> goAnoma bl x
       Constant x -> goConst bl x
@@ -85,6 +86,11 @@ inferType tab funInfo = goInfer mempty
           OpUInt8ToInt -> checkUnop mkTypeUInt8 mkTypeInteger
           OpIntToUInt8 -> checkUnop mkTypeInteger mkTypeUInt8
 
+    goByteArray :: BinderList Type -> NodeByteArray -> Sem r Type
+    goByteArray bl NodeByteArray {..} = do
+      mapM_ (\arg -> checkType bl arg TyDynamic) _nodeByteArrayArgs
+      return TyDynamic
+
     goCairo :: BinderList Type -> NodeCairo -> Sem r Type
     goCairo bl NodeCairo {..} = do
       mapM_ (\arg -> checkType bl arg TyDynamic) _nodeCairoArgs
@@ -104,6 +110,7 @@ inferType tab funInfo = goInfer mempty
       ConstUnit {} -> return TyUnit
       ConstVoid {} -> return TyVoid
       ConstUInt8 {} -> return mkTypeUInt8
+      ConstByteArray {} -> return TyByteArray
 
     goMemRef :: BinderList Type -> NodeMemRef -> Sem r Type
     goMemRef bl NodeMemRef {..} = case _nodeMemRef of
diff --git a/src/Juvix/Compiler/Tree/Translation/FromCore.hs b/src/Juvix/Compiler/Tree/Translation/FromCore.hs
index 587b4241df..52e5ead2bf 100644
--- a/src/Juvix/Compiler/Tree/Translation/FromCore.hs
+++ b/src/Juvix/Compiler/Tree/Translation/FromCore.hs
@@ -87,6 +87,8 @@ genCode infoTable fi =
         mkConst (ConstField fld)
       Core.Constant _ (Core.ConstUInt8 i) ->
         mkConst (ConstUInt8 i)
+      Core.Constant _ (Core.ConstByteArray bs) ->
+        mkConst (ConstByteArray bs)
 
     goApps :: Int -> BinderList MemRef -> Core.Apps -> Node
     goApps tempSize refs Core.Apps {..} =
@@ -140,6 +142,13 @@ genCode infoTable fi =
 
     goBuiltinApp :: Int -> BinderList MemRef -> Core.BuiltinApp -> Node
     goBuiltinApp tempSize refs Core.BuiltinApp {..}
+      | Core.builtinIsByteArray _builtinAppOp =
+          ByteArray $
+            NodeByteArray
+              { _nodeByteArrayInfo = mempty,
+                _nodeByteArrayOpcode = genByteArrayOp _builtinAppOp,
+                _nodeByteArrayArgs = args
+              }
       | Core.builtinIsCairo _builtinAppOp =
           Cairo $
             NodeCairo
@@ -308,6 +317,12 @@ genCode infoTable fi =
       Core.OpUInt8ToInt -> PrimUnop OpUInt8ToInt
       _ -> impossible
 
+    genByteArrayOp :: Core.BuiltinOp -> ByteArrayOp
+    genByteArrayOp = \case
+      Core.OpByteArrayFromListByte -> OpByteArrayFromListUInt8
+      Core.OpByteArrayLength -> OpByteArrayLength
+      _ -> impossible
+
     genCairoOp :: Core.BuiltinOp -> CairoOp
     genCairoOp = \case
       Core.OpPoseidonHash -> OpCairoPoseidon
@@ -361,6 +376,8 @@ convertPrimitiveType = \case
     TyString
   Core.PrimField ->
     TyField
+  Core.PrimByteArray ->
+    TyByteArray
 
 -- | `convertNestedType` ensures that the conversion of a type with Dynamic in the
 -- target is curried. The result of `convertType 0 ty` is always uncurried.
diff --git a/src/Juvix/Compiler/Tree/Translation/FromSource.hs b/src/Juvix/Compiler/Tree/Translation/FromSource.hs
index 77f1d99c15..2a42f354d2 100644
--- a/src/Juvix/Compiler/Tree/Translation/FromSource.hs
+++ b/src/Juvix/Compiler/Tree/Translation/FromSource.hs
@@ -53,6 +53,7 @@ parseNode ::
 parseNode =
   (Binop <$> parseBinop)
     <|> (Unop <$> parseUnop)
+    <|> (ByteArray <$> parseByteArray)
     <|> (Anoma <$> parseAnoma)
     <|> (Cairo <$> parseCairo)
     <|> (Constant <$> parseConst)
@@ -119,6 +120,23 @@ parseUnaryOp kwd op = do
   arg <- parens parseNode
   return $ NodeUnop (NodeInfo (Just loc)) op arg
 
+parseByteArray ::
+  (Members '[Reader ParserSig, InfoTableBuilder, State LocalParams] r) =>
+  ParsecS r NodeByteArray
+parseByteArray =
+  parseByteArrayOp kwByteArrayFromListUInt8 OpByteArrayFromListUInt8
+    <|> parseByteArrayOp kwByteArrayLength OpByteArrayLength
+
+parseByteArrayOp ::
+  (Members '[Reader ParserSig, InfoTableBuilder, State LocalParams] r) =>
+  Keyword ->
+  ByteArrayOp ->
+  ParsecS r NodeByteArray
+parseByteArrayOp kwd op = do
+  loc <- onlyInterval (kw kwd)
+  args <- parseArgs
+  return $ NodeByteArray (NodeInfo (Just loc)) op args
+
 parseAnoma ::
   (Members '[Reader ParserSig, InfoTableBuilder, State LocalParams] r) =>
   ParsecS r NodeAnoma
diff --git a/src/Juvix/Compiler/Tree/Translation/FromSource/Base.hs b/src/Juvix/Compiler/Tree/Translation/FromSource/Base.hs
index 603a13ecdd..d3b3fa5882 100644
--- a/src/Juvix/Compiler/Tree/Translation/FromSource/Base.hs
+++ b/src/Juvix/Compiler/Tree/Translation/FromSource/Base.hs
@@ -309,6 +309,7 @@ typeNamed = do
     "bool" -> return mkTypeBool
     "string" -> return TyString
     "unit" -> return TyUnit
+    "uint8" -> return mkTypeUInt8
     _ -> do
       idt <- lift $ getIdent' @t @e txt
       case idt of
@@ -316,13 +317,18 @@ typeNamed = do
         _ -> parseFailure off ("not a type: " ++ fromText txt)
 
 constant :: ParsecS r Constant
-constant = fieldValue <|> integerValue <|> boolValue <|> stringValue <|> unitValue <|> voidValue
+constant = fieldValue <|> uint8Value <|> integerValue <|> boolValue <|> stringValue <|> unitValue <|> voidValue
 
 fieldValue :: ParsecS r Constant
 fieldValue = P.try $ do
   (i, _) <- field
   return $ ConstField (fieldFromInteger defaultFieldSize i)
 
+uint8Value :: ParsecS r Constant
+uint8Value = P.try $ do
+  (i, _) <- uint8
+  return $ ConstUInt8 (fromInteger i)
+
 integerValue :: ParsecS r Constant
 integerValue = do
   i <- (^. withLocParam) <$> integer
diff --git a/src/Juvix/Compiler/Tree/Translation/FromSource/Lexer/Base.hs b/src/Juvix/Compiler/Tree/Translation/FromSource/Lexer/Base.hs
index 918c82a878..d9869de00b 100644
--- a/src/Juvix/Compiler/Tree/Translation/FromSource/Lexer/Base.hs
+++ b/src/Juvix/Compiler/Tree/Translation/FromSource/Lexer/Base.hs
@@ -31,6 +31,9 @@ number = number' integer
 field :: ParsecS r (Integer, Interval)
 field = lexemeInterval field'
 
+uint8 :: ParsecS r (Integer, Interval)
+uint8 = lexemeInterval uint8'
+
 string :: ParsecS r (Text, Interval)
 string = lexemeInterval string'
 
diff --git a/src/Juvix/Data/CodeAnn.hs b/src/Juvix/Data/CodeAnn.hs
index 49f2ed181e..37cfb4f358 100644
--- a/src/Juvix/Data/CodeAnn.hs
+++ b/src/Juvix/Data/CodeAnn.hs
@@ -79,6 +79,9 @@ primitive = annotate (AnnKind KNameAxiom) . pretty
 keyword :: Text -> Doc Ann
 keyword = annotate AnnKeyword . pretty
 
+constructor :: Text -> Doc Ann
+constructor = annotate (AnnKind KNameConstructor) . pretty
+
 kwNotMutual :: Doc Ann
 kwNotMutual = keyword Str.notMutual
 
diff --git a/src/Juvix/Data/Keyword/All.hs b/src/Juvix/Data/Keyword/All.hs
index a48048b923..e8697ff61e 100644
--- a/src/Juvix/Data/Keyword/All.hs
+++ b/src/Juvix/Data/Keyword/All.hs
@@ -277,6 +277,9 @@ kwPrealloc = asciiKw Str.prealloc
 kwArgsNum :: Keyword
 kwArgsNum = asciiKw Str.instrArgsNum
 
+kwByteArrayFromListUInt8 :: Keyword
+kwByteArrayFromListUInt8 = asciiKw Str.instrByteArrayFromListUInt8
+
 kwPoseidon :: Keyword
 kwPoseidon = asciiKw Str.instrPoseidon
 
@@ -463,6 +466,12 @@ kwAnomaSignDetached = asciiKw Str.anomaSignDetached
 kwAnomaVerifyWithMessage :: Keyword
 kwAnomaVerifyWithMessage = asciiKw Str.anomaVerifyWithMessage
 
+kwByteArrayFromListByte :: Keyword
+kwByteArrayFromListByte = asciiKw Str.byteArrayFromListByte
+
+kwByteArrayLength :: Keyword
+kwByteArrayLength = asciiKw Str.byteArrayLength
+
 delimBraceL :: Keyword
 delimBraceL = mkDelim Str.braceL
 
diff --git a/src/Juvix/Extra/Strings.hs b/src/Juvix/Extra/Strings.hs
index df249563a9..fa064e51b9 100644
--- a/src/Juvix/Extra/Strings.hs
+++ b/src/Juvix/Extra/Strings.hs
@@ -185,6 +185,15 @@ byteToNat = "byte-to-nat"
 byteFromNat :: (IsString s) => s
 byteFromNat = "byte-from-nat"
 
+byteArray :: (IsString s) => s
+byteArray = "bytearray"
+
+byteArrayFromListByte :: (IsString s) => s
+byteArrayFromListByte = "bytearray-from-list-byte"
+
+byteArrayLength :: (IsString s) => s
+byteArrayLength = "bytearray-length"
+
 nat :: (IsString s) => s
 nat = "nat"
 
@@ -728,6 +737,9 @@ fun_ = "function"
 integer :: (IsString s) => s
 integer = "integer"
 
+uint8 :: (IsString s) => s
+uint8 = "uint8"
+
 bool :: (IsString s) => s
 bool = "bool"
 
@@ -794,6 +806,12 @@ instrUInt8ToInt = "u8toi"
 instrIntToUInt8 :: (IsString s) => s
 instrIntToUInt8 = "itou8"
 
+instrByteArrayFromListUInt8 :: (IsString s) => s
+instrByteArrayFromListUInt8 = "bytearray-from-list-uint8"
+
+instrByteArrayLength :: (IsString s) => s
+instrByteArrayLength = "bytearray-length"
+
 instrShow :: (IsString s) => s
 instrShow = "show"
 
@@ -923,6 +941,12 @@ nil = "nil"
 cons :: (IsString s) => s
 cons = "cons"
 
+builtinListCons :: (IsString s) => s
+builtinListCons = "builtinListCons"
+
+builtinListNil :: (IsString s) => s
+builtinListNil = "builtinListNil"
+
 nothing :: (IsString s) => s
 nothing = "nothing"
 
diff --git a/test/Anoma/Compilation/Positive.hs b/test/Anoma/Compilation/Positive.hs
index fea8d489cf..9d97cdfcf7 100644
--- a/test/Anoma/Compilation/Positive.hs
+++ b/test/Anoma/Compilation/Positive.hs
@@ -612,5 +612,22 @@ allTests =
             [nock| 3 |],
             [nock| 240 |],
             [nock| [1 238 3 2 nil] |]
+          ],
+      mkAnomaCallTest
+        "Test082: ByteArray"
+        $(mkRelDir ".")
+        $(mkRelFile "test082.juvix")
+        []
+        $ checkOutput
+          [ [nock| 0 |],
+            [nock| [0 0] |],
+            [nock| 3 |],
+            [nock| [3 0] |],
+            [nock| 4 |],
+            [nock| [4 1] |],
+            [nock| 2 |],
+            [nock| [2 258] |],
+            [nock| 1 |],
+            [nock| [1 0] |]
           ]
     ]
diff --git a/test/Core/Asm/Positive.hs b/test/Core/Asm/Positive.hs
index 6d7a081f45..8fee238a47 100644
--- a/test/Core/Asm/Positive.hs
+++ b/test/Core/Asm/Positive.hs
@@ -8,7 +8,10 @@ allTests :: TestTree
 allTests = testGroup "JuvixCore to JuvixAsm positive tests" (map liftTest (Eval.filterOutTests ignoredTests Eval.compilableTests))
 
 ignoredTests :: [String]
-ignoredTests = ["Test062: Anoma"]
+ignoredTests =
+  [ "Test062: Anoma",
+    "Test064: ByteArray"
+  ]
 
 liftTest :: Eval.PosTest -> TestTree
 liftTest _testEval =
diff --git a/test/Core/Compile/Positive.hs b/test/Core/Compile/Positive.hs
index f9ee3011dc..85d4276b27 100644
--- a/test/Core/Compile/Positive.hs
+++ b/test/Core/Compile/Positive.hs
@@ -7,7 +7,7 @@ import Core.Eval.Positive qualified as Eval
 allTests :: TestTree
 allTests = testGroup "JuvixCore compilation tests" (map liftTest (Eval.filterOutTests ignoredTests Eval.compilableTests))
 
--- Arbitrary precision integers and fields not yet supported
+-- Arbitrary precision integers, fields, Anoma ops, and bytearrayss not yet supported
 ignoredTests :: [String]
 ignoredTests =
   [ "Test011: Tail recursion: Fibonacci numbers in linear time",
@@ -17,7 +17,8 @@ ignoredTests =
     "Test036: Big numbers",
     "Test040: LetRec - fib, fact",
     "Test061: Fields",
-    "Test062: Anoma"
+    "Test062: Anoma",
+    "Test064: ByteArray"
   ]
 
 liftTest :: Eval.PosTest -> TestTree
diff --git a/test/Core/Eval/Positive.hs b/test/Core/Eval/Positive.hs
index ccd2de8f68..a8451a1884 100644
--- a/test/Core/Eval/Positive.hs
+++ b/test/Core/Eval/Positive.hs
@@ -352,5 +352,15 @@ tests =
       "Test062: Anoma"
       $(mkRelDir ".")
       $(mkRelFile "test062.jvc")
-      $(mkRelFile "out/test062.out")
+      $(mkRelFile "out/test062.out"),
+    PosTest
+      "Test063: UInt8"
+      $(mkRelDir ".")
+      $(mkRelFile "test063.jvc")
+      $(mkRelFile "out/test063.out"),
+    PosTest
+      "Test064: ByteArray"
+      $(mkRelDir ".")
+      $(mkRelFile "test064.jvc")
+      $(mkRelFile "out/test064.out")
   ]
diff --git a/test/Nockma/Compile/Tree/Positive.hs b/test/Nockma/Compile/Tree/Positive.hs
index 74e3ea60ee..dc72690406 100644
--- a/test/Nockma/Compile/Tree/Positive.hs
+++ b/test/Nockma/Compile/Tree/Positive.hs
@@ -49,7 +49,7 @@ testDescr Tree.PosTest {..} =
 
 -- | Tests which require Nockma-specific expected output files
 testsConstr :: [Int]
-testsConstr = [9, 28, 35]
+testsConstr = [9, 28, 35, 40]
 
 testsNegativeInteger :: [Int]
 testsNegativeInteger = [16]
diff --git a/test/Nockma/Eval/Positive.hs b/test/Nockma/Eval/Positive.hs
index a9ccd12953..1f2cd66369 100644
--- a/test/Nockma/Eval/Positive.hs
+++ b/test/Nockma/Eval/Positive.hs
@@ -269,7 +269,16 @@ juvixCallingConventionTests =
                lenR :: Term Natural = nockIntegralLiteral (length r)
                tupR = OpQuote # foldTerms (toNock <$> r)
             in compilerTest "appendToTuple (left empty, right-nonempty)" (appendToTuple (OpQuote # nockNilTagged "test-appendtotuple") (nockNatLiteral 0) tupR lenR) (eqNock res),
-           compilerTest "stdlib cat" (callStdlib StdlibCatBytes [nockNatLiteral 2, nockNatLiteral 1]) (eqNock [nock| 258 |])
+           compilerTest "stdlib cat" (callStdlib StdlibCatBytes [nockNatLiteral 2, nockNatLiteral 1]) (eqNock [nock| 258 |]),
+           compilerTest "fold bytes empty" (callStdlib StdlibFoldBytes [OpQuote # makeList []]) (eqNock [nock| 0 |]),
+           compilerTest "fold bytes [1, 0, 0] == 1" (callStdlib StdlibFoldBytes [OpQuote # makeList (toNock @Natural <$> [1, 0, 0])]) (eqNock [nock| 1 |]),
+           compilerTest "fold bytes single byte" (callStdlib StdlibFoldBytes [OpQuote # makeList (toNock @Natural <$> [123])]) (eqNock [nock| 123 |]),
+           compilerTest "fold bytes [0, 1] == 256" (callStdlib StdlibFoldBytes [OpQuote # makeList (toNock @Natural <$> [0, 1])]) (eqNock [nock| 256 |]),
+           compilerTest "fold bytes [5, 1] == 261" (callStdlib StdlibFoldBytes [OpQuote # makeList (toNock @Natural <$> [5, 1])]) (eqNock [nock| 261 |]),
+           compilerTest "fold bytes [0, 1, 0] == 256" (callStdlib StdlibFoldBytes [OpQuote # makeList (toNock @Natural <$> [0, 1, 0])]) (eqNock [nock| 256 |]),
+           compilerTest "length [] == 0" (callStdlib StdlibLengthList [OpQuote # makeList []]) (eqNock [nock| 0 |]),
+           compilerTest "length [10] == 1" (callStdlib StdlibLengthList [OpQuote # makeList [[nock| 10 |]]]) (eqNock [nock| 1 |]),
+           compilerTest "length [[1 2, 3], 0] == 2" (callStdlib StdlibLengthList [OpQuote # makeList [[nock| [1 2 3] |], [nock| 0 |]]]) (eqNock [nock| 2 |])
          ]
 
 unitTests :: [Test]
diff --git a/test/Tree/Asm/Positive.hs b/test/Tree/Asm/Positive.hs
index cea544c9c8..0979093b1d 100644
--- a/test/Tree/Asm/Positive.hs
+++ b/test/Tree/Asm/Positive.hs
@@ -15,8 +15,11 @@ testDescr Eval.PosTest {..} =
           _testAssertion = Steps $ treeAsmAssertion file' expected'
         }
 
+ignoredTests :: [String]
+ignoredTests = ["Test040: ByteArray"]
+
 allTests :: TestTree
 allTests =
   testGroup
     "JuvixTree to JuvixAsm positive tests"
-    (map (mkTest . testDescr) Eval.tests)
+    (map (mkTest . testDescr) (Eval.filterOutTests ignoredTests Eval.tests))
diff --git a/test/Tree/Eval/Positive.hs b/test/Tree/Eval/Positive.hs
index 8cf0797ed3..659f3a9fbd 100644
--- a/test/Tree/Eval/Positive.hs
+++ b/test/Tree/Eval/Positive.hs
@@ -229,5 +229,15 @@ tests =
       "Test038: Apply & argsnum"
       $(mkRelDir ".")
       $(mkRelFile "test038.jvt")
-      $(mkRelFile "out/test038.out")
+      $(mkRelFile "out/test038.out"),
+    PosTest
+      "Test039: UInt8"
+      $(mkRelDir ".")
+      $(mkRelFile "test039.jvt")
+      $(mkRelFile "out/test039.out"),
+    PosTest
+      "Test040: ByteArray"
+      $(mkRelDir ".")
+      $(mkRelFile "test040.jvt")
+      $(mkRelFile "out/test040.out")
   ]
diff --git a/tests/Anoma/Compilation/positive/test082.juvix b/tests/Anoma/Compilation/positive/test082.juvix
new file mode 100644
index 0000000000..723c87ebb1
--- /dev/null
+++ b/tests/Anoma/Compilation/positive/test082.juvix
@@ -0,0 +1,35 @@
+module test082;
+
+import Stdlib.Prelude open;
+import Stdlib.Debug.Trace open;
+
+builtin bytearray
+axiom ByteArray : Type;
+
+builtin bytearray-from-list-byte
+axiom mkByteArray : List Byte -> ByteArray;
+
+builtin bytearray-length
+axiom size : ByteArray -> Nat;
+
+bs0 : ByteArray := mkByteArray [];
+
+bs1 : ByteArray := mkByteArray [0x0; 0x0; 0x0];
+
+bs2 : ByteArray := mkByteArray [0x1; 0x0; 0x0; 0x0];
+
+bs3 : ByteArray := mkByteArray [0x2; 0x1];
+
+bs4 : ByteArray := mkByteArray [0x100];
+
+main : ByteArray :=
+  trace (size bs0)
+    >-> trace bs0
+    >-> trace (size bs1)
+    >-> trace bs1
+    >-> trace (size bs2)
+    >-> trace bs2
+    >-> trace (size bs3)
+    >-> trace bs3
+    >-> trace (size bs4)
+    >-> bs4;
diff --git a/tests/Core/positive/out/test064.out b/tests/Core/positive/out/test064.out
new file mode 100644
index 0000000000..a359f595be
--- /dev/null
+++ b/tests/Core/positive/out/test064.out
@@ -0,0 +1,2 @@
+bytearray-from-list-byte (builtinListCons UInt8 1 (builtinListCons UInt8 2 (builtinListNil UInt8)))
+2
diff --git a/tests/Core/positive/test063.jvc b/tests/Core/positive/test063.jvc
index 246b87d2c7..fb604e8009 100644
--- a/tests/Core/positive/test063.jvc
+++ b/tests/Core/positive/test063.jvc
@@ -1,5 +1,5 @@
 -- UInt8
 
-def f := \x x;
+def f : UInt8 -> UInt8 := \x x;
 
 f 257u8
diff --git a/tests/Core/positive/test064.jvc b/tests/Core/positive/test064.jvc
new file mode 100644
index 0000000000..872059ba52
--- /dev/null
+++ b/tests/Core/positive/test064.jvc
@@ -0,0 +1,6 @@
+
+def writeLn := \x write x >> write "\n";
+
+def bs : ByteArray := bytearray-from-list-byte (builtinListCons UInt8 257u8 (builtinListCons UInt8 2u8 (builtinListNil UInt8)));
+
+writeLn bs >> writeLn (bytearray-length bs)
diff --git a/tests/Tree/positive/out/test039.out b/tests/Tree/positive/out/test039.out
new file mode 100644
index 0000000000..d00491fd7e
--- /dev/null
+++ b/tests/Tree/positive/out/test039.out
@@ -0,0 +1 @@
+1
diff --git a/tests/Tree/positive/out/test040.nockma.out b/tests/Tree/positive/out/test040.nockma.out
new file mode 100644
index 0000000000..37b4d37e4c
--- /dev/null
+++ b/tests/Tree/positive/out/test040.nockma.out
@@ -0,0 +1,2 @@
+2
+[2 258]
diff --git a/tests/Tree/positive/out/test040.out b/tests/Tree/positive/out/test040.out
new file mode 100644
index 0000000000..9e898d76a6
--- /dev/null
+++ b/tests/Tree/positive/out/test040.out
@@ -0,0 +1,2 @@
+2
+alloc[cons](2u8, alloc[cons](1u8, alloc[nil]()))
diff --git a/tests/Tree/positive/test039.jvt b/tests/Tree/positive/test039.jvt
new file mode 100644
index 0000000000..5c033a5a5b
--- /dev/null
+++ b/tests/Tree/positive/test039.jvt
@@ -0,0 +1,11 @@
+
+function id(uint8) : uint8;
+function main() : *
+
+function id(uint8) : uint8 {
+  arg[0]
+}
+
+function main() : * {
+  call[id](257u8)
+}
diff --git a/tests/Tree/positive/test040.jvt b/tests/Tree/positive/test040.jvt
new file mode 100644
index 0000000000..1450b99bd5
--- /dev/null
+++ b/tests/Tree/positive/test040.jvt
@@ -0,0 +1,12 @@
+-- ByteArray
+
+type list {
+  nil : list;
+  cons : * -> list -> list;
+}
+
+function main() : * {
+  save(bytearray-from-list-uint8(alloc[cons](258u8, alloc[cons](1u8, alloc[nil]())))) {
+    seq(trace(bytearray-length(tmp[0])), tmp[0])
+  }
+}