diff --git a/src/Simplex/Messaging/Builder.hs b/src/Simplex/Messaging/Builder.hs
new file mode 100644
index 000000000..4d839db46
--- /dev/null
+++ b/src/Simplex/Messaging/Builder.hs
@@ -0,0 +1,56 @@
+{-# LANGUAGE StrictData #-}
+
+module Simplex.Messaging.Builder
+  ( Builder (length, builder),
+    byteString,
+    lazyByteString,
+    word16BE,
+    char8,
+    toLazyByteString,
+  )
+where
+
+import qualified Data.ByteString as B
+import qualified Data.ByteString.Builder as BB
+import qualified Data.ByteString.Lazy as LB
+import Data.Word (Word16)
+
+
+-- length-aware builder
+data Builder = Builder {length :: Int, builder :: BB.Builder}
+
+unsafeBuilder :: Int -> BB.Builder -> Builder
+unsafeBuilder = Builder
+{-# INLINE unsafeBuilder #-}
+
+instance Semigroup Builder where
+  Builder l1 b1 <> Builder l2 b2 = Builder (l1 + l2) (b1 <> b2)
+  {-# INLINE (<>) #-}
+
+instance Monoid Builder where
+  mempty = Builder 0 mempty
+  {-# INLINE mempty #-}
+  mconcat bldrs = Builder (sum ls) (mconcat bs)
+    where
+      (ls, bs) = foldr (\(Builder l b) ~(ls, bs) -> (l : ls, b : bs)) ([], []) bldrs
+  {-# INLINE mconcat #-}
+
+byteString :: B.ByteString -> Builder
+byteString s = Builder (B.length s) (BB.byteString s)
+{-# INLINE byteString #-}
+
+lazyByteString :: LB.ByteString -> Builder
+lazyByteString s = Builder (fromIntegral $ LB.length s) (BB.lazyByteString s)
+{-# INLINE lazyByteString #-}
+
+word16BE :: Word16 -> Builder
+word16BE = Builder 2 . BB.word16BE
+{-# INLINE word16BE #-}
+
+char8 :: Char -> Builder
+char8 = Builder 1 . BB.char8
+{-# INLINE char8 #-}
+
+toLazyByteString :: Builder -> LB.ByteString
+toLazyByteString = BB.toLazyByteString . builder
+{-# INLINE toLazyByteString #-}