diff --git a/CHANGELOG.md b/CHANGELOG.md
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--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,11 @@
+# Changelog for `yaftee-conduit-mono-traversable`
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to the
+[Haskell Package Versioning Policy](https://pvp.haskell.org/).
+
+## Unreleased
+
+## 0.1.0.0 - YYYY-MM-DD
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,26 @@
+Copyright 2025 Yoshikuni Jujo
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1.  Redistributions of source code must retain the above copyright notice, this
+    list of conditions and the following disclaimer.
+
+2.  Redistributions in binary form must reproduce the above copyright notice,
+    this list of conditions and the following disclaimer in the documentation
+    and/or other materials provided with the distribution.
+
+3.  Neither the name of the copyright holder nor the names of its contributors
+    may be used to endorse or promote products derived from this software
+    without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
@@ -0,0 +1,3 @@
+# yaftee-conduit-mono-traversable
+
+MonoTraversable tools for Yaftee Conduit.
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/src/Control/Monad/Yaftee/Pipe/MonoTraversable.hs b/src/Control/Monad/Yaftee/Pipe/MonoTraversable.hs
new file mode 100644
--- /dev/null
+++ b/src/Control/Monad/Yaftee/Pipe/MonoTraversable.hs
@@ -0,0 +1,61 @@
+{-# LANGUAGE ImportQualifiedPost #-}
+{-# LANGUAGE BlockArguments, LambdaCase #-}
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE RequiredTypeArguments #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# OPTIONS_GHC -Wall -fno-warn-tabs #-}
+
+module Control.Monad.Yaftee.Pipe.MonoTraversable (
+
+	lengthRun, length, length', Length, lengthFromInt64, lengthToInt64
+
+	) where
+
+import Prelude hiding (length)
+import Control.Monad
+import Control.Monad.Fix
+import Control.Monad.Yaftee.Eff qualified as Eff
+import Control.Monad.Yaftee.Pipe qualified as Pipe
+import Control.Monad.Yaftee.State qualified as State
+import Control.HigherOpenUnion qualified as U
+import Data.HigherFunctor qualified as HFunctor
+import Data.MonoTraversable
+import Data.Int
+
+lengthRun :: forall nm es i o r . HFunctor.Loose (U.U es) =>
+	Eff.E (State.Named nm Length ': es) i o r -> Eff.E es i o (r, Length)
+lengthRun = (`State.runN` (0 :: Length))
+
+length :: forall nm -> (
+	MonoFoldable mono,
+	U.Member Pipe.P es,
+	U.Member (State.Named nm Length) es ) =>
+	Eff.E es mono mono r
+length nm = do
+	State.putN nm $ Length 0
+	forever $ Pipe.await >>= \xs ->
+		State.modifyN nm (+ Length (olength64 xs)) >> Pipe.yield xs
+
+length' :: forall nm -> (
+	MonoFoldable mono,
+	U.Member Pipe.P es,
+	U.Member (State.Named nm Length) es ) =>
+	Eff.E es mono mono ()
+length' nm = do
+	State.putN nm $ Length 0
+	fix \go -> Pipe.awaitMaybe >>= \case
+		Nothing -> pure ()
+		Just xs -> (>> go) do
+			State.modifyN nm (+ Length (olength64 xs))
+			Pipe.yield xs
+
+newtype Length = Length { unLength :: Int64 }
+	deriving (Show, Eq, Ord, Enum, Num, Real, Integral)
+
+lengthToInt64 :: Length -> Int64
+lengthToInt64 = unLength
+
+lengthFromInt64 :: Int64 -> Length
+lengthFromInt64 = Length
diff --git a/src/Control/Monad/Yaftee/Pipe/MonoTraversable/Crc32.hs b/src/Control/Monad/Yaftee/Pipe/MonoTraversable/Crc32.hs
new file mode 100644
--- /dev/null
+++ b/src/Control/Monad/Yaftee/Pipe/MonoTraversable/Crc32.hs
@@ -0,0 +1,57 @@
+{-# LANGUAGE ImportQualifiedPost #-}
+{-# LANGUAGE BlockArguments, LambdaCase #-}
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE RequiredTypeArguments #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# OPTIONS_GHC -Wall -fno-warn-tabs #-}
+
+module Control.Monad.Yaftee.Pipe.MonoTraversable.Crc32 (
+
+	run, complement, crc32, crc32',
+
+	step
+
+	) where
+
+import Control.Monad
+import Control.Monad.Fix
+import Control.Monad.Yaftee.Eff qualified as Eff
+import Control.Monad.Yaftee.Pipe qualified as Pipe
+import Control.Monad.Yaftee.State qualified as State
+import Control.HigherOpenUnion qualified as U
+import Data.HigherFunctor qualified as HFunctor
+import Data.MonoTraversable
+import Data.Word
+import Data.Word.Crc32 qualified as Crc32
+
+run :: forall nm es i o r . HFunctor.Loose (U.U es) =>
+	Eff.E (State.Named nm Crc32.C ': es) i o r -> Eff.E es i o (r, Crc32.C)
+run = (`State.runN` Crc32.initial)
+
+complement ::
+	forall nm -> U.Member (State.Named nm Crc32.C) es => Eff.E es i o ()
+complement nm = State.modifyN nm Crc32.complement
+
+crc32 :: forall nm -> (
+	MonoFoldable mono, Element mono ~ Word8,
+	U.Member Pipe.P es, U.Member (State.Named nm Crc32.C) es ) =>
+	Eff.E es mono mono r
+crc32 nm = do
+	State.putN nm Crc32.initial
+	forever $ Pipe.await >>= \s ->
+		State.modifyN nm (`step` s) >> Pipe.yield s
+
+crc32' :: forall nm -> (
+	MonoFoldable mono, Element mono ~ Word8,
+	U.Member Pipe.P es, U.Member (State.Named nm Crc32.C) es ) =>
+	Eff.E es mono mono ()
+crc32' nm = do
+	State.putN nm Crc32.initial
+	fix \go -> Pipe.awaitMaybe >>= \case
+		Nothing -> pure ()
+		Just bs -> (>> go)
+			$ State.modifyN nm (`step` bs) >> Pipe.yield bs
+
+step :: (MonoFoldable mono, Element mono ~ Word8) => Crc32.C -> mono -> Crc32.C
+step = ofoldl' Crc32.step
diff --git a/test/Spec.hs b/test/Spec.hs
new file mode 100644
--- /dev/null
+++ b/test/Spec.hs
@@ -0,0 +1,2 @@
+main :: IO ()
+main = putStrLn "Test suite not yet implemented"
diff --git a/yaftee-conduit-mono-traversable.cabal b/yaftee-conduit-mono-traversable.cabal
new file mode 100644
--- /dev/null
+++ b/yaftee-conduit-mono-traversable.cabal
@@ -0,0 +1,69 @@
+cabal-version: 2.2
+
+-- This file has been generated from package.yaml by hpack version 0.38.1.
+--
+-- see: https://github.com/sol/hpack
+
+name:           yaftee-conduit-mono-traversable
+version:        0.1.0.0
+synopsis:       Mono traversable tools for Yaftee Conduit
+description:    Please see the README on GitHub at <https://github.com/YoshikuniJujo/yaftee-conduit-mono-traversable#readme>
+category:       Control
+homepage:       https://github.com/YoshikuniJujo/yaftee-conduit-mono-traversable#readme
+bug-reports:    https://github.com/YoshikuniJujo/yaftee-conduit-mono-traversable/issues
+author:         Yoshikuni Jujo
+maintainer:     yoshikuni.jujo@gmail.com
+copyright:      (c) 2025 Yoshikuni Jujo
+license:        BSD-3-Clause
+license-file:   LICENSE
+build-type:     Simple
+extra-source-files:
+    README.md
+extra-doc-files:
+    CHANGELOG.md
+
+source-repository head
+  type: git
+  location: https://github.com/YoshikuniJujo/yaftee-conduit-mono-traversable
+
+library
+  exposed-modules:
+      Control.Monad.Yaftee.Pipe.MonoTraversable
+      Control.Monad.Yaftee.Pipe.MonoTraversable.Crc32
+  other-modules:
+      Paths_yaftee_conduit_mono_traversable
+  autogen-modules:
+      Paths_yaftee_conduit_mono_traversable
+  hs-source-dirs:
+      src
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints
+  build-depends:
+      base >=4.7 && <5
+    , higher-order-open-union ==0.1.*
+    , mono-traversable ==1.0.*
+    , tools-yj ==0.1.*
+    , yaftee ==0.1.*
+    , yaftee-basic-monads ==0.1.*
+    , yaftee-conduit ==0.1.*
+  default-language: Haskell2010
+
+test-suite yaftee-conduit-mono-traversable-test
+  type: exitcode-stdio-1.0
+  main-is: Spec.hs
+  other-modules:
+      Paths_yaftee_conduit_mono_traversable
+  autogen-modules:
+      Paths_yaftee_conduit_mono_traversable
+  hs-source-dirs:
+      test
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -threaded -rtsopts -with-rtsopts=-N
+  build-depends:
+      base >=4.7 && <5
+    , higher-order-open-union ==0.1.*
+    , mono-traversable ==1.0.*
+    , tools-yj ==0.1.*
+    , yaftee ==0.1.*
+    , yaftee-basic-monads ==0.1.*
+    , yaftee-conduit ==0.1.*
+    , yaftee-conduit-mono-traversable
+  default-language: Haskell2010