diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,3 @@
+## 0.1.0.0 -- 2021-01-XX
+
+* First version. Released on an unsuspecting world.
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,5 @@
+Apache-2.0 OR MPL-2.0
+
+---
+
+See https://github.com/mizunashi-mana/tlex/blob/master/LICENSE
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
@@ -0,0 +1,1 @@
+See https://hackage.haskell.org/package/tlex
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,6 @@
+module Main where
+
+import           Distribution.Extra.Doctest (defaultMainWithDoctests)
+
+main :: IO ()
+main = defaultMainWithDoctests "doctest"
diff --git a/src/Language/Lexer/Tlex/Plugin/Debug.hs b/src/Language/Lexer/Tlex/Plugin/Debug.hs
new file mode 100644
--- /dev/null
+++ b/src/Language/Lexer/Tlex/Plugin/Debug.hs
@@ -0,0 +1,107 @@
+module Language.Lexer.Tlex.Plugin.Debug (
+    outputDfaToDot,
+    Graphviz.outputAst,
+) where
+
+import           Language.Lexer.Tlex.Prelude
+
+import qualified Data.HashMap.Strict                       as HashMap
+import qualified Data.IntMap.Strict                        as IntMap
+import qualified Data.IntSet                               as IntSet
+import qualified Language.Lexer.Tlex.Data.EnumMap          as EnumMap
+import qualified Language.Lexer.Tlex.Machine.DFA           as DFA
+import qualified Language.Lexer.Tlex.Machine.State         as MState
+import qualified Language.Lexer.Tlex.Plugin.Debug.Graphviz as Graphviz
+import qualified Prelude
+
+
+newtype EdgeBuilder = EdgeBuilder
+    { unEdgeBuilder :: HashMap.HashMap
+        (MState.StateNum, MState.StateNum)
+        IntSet.IntSet
+    }
+
+instance Semigroup EdgeBuilder where
+    EdgeBuilder m1 <> EdgeBuilder m2 = EdgeBuilder do HashMap.unionWith (<>) m1 m2
+
+instance Monoid EdgeBuilder where
+    mempty = EdgeBuilder HashMap.empty
+
+edgeBuilder :: MState.StateNum -> Int -> MState.StateNum -> EdgeBuilder
+edgeBuilder sf lb st = EdgeBuilder do HashMap.singleton (sf, st) do IntSet.singleton lb
+
+outputDfaToDot :: DFA.DFA a -> Graphviz.Ast
+outputDfaToDot dfa = Graphviz.Ast
+    { Graphviz.nodes = initialNode :
+        [ node sn dst
+        | (sn, dst) <- MState.arrayAssocs do DFA.dfaTrans dfa
+        ]
+    , Graphviz.edges = initialEdges ++
+        concatMap
+            do \(sn, dst) -> edges sn dst
+            do MState.arrayAssocs do DFA.dfaTrans dfa
+    }
+    where
+        initialNode = Graphviz.Node
+            { Graphviz.nodeId = "init"
+            , Graphviz.nodeLabel = Nothing
+            , Graphviz.nodeShape = Nothing
+            }
+
+        node sn dst = Graphviz.Node
+            { Graphviz.nodeId = show do fromEnum sn
+            , Graphviz.nodeLabel = Nothing
+            , Graphviz.nodeShape = case DFA.dstAccepts dst of
+                [] -> Nothing
+                _  -> Just Graphviz.DoubleCircle
+            }
+
+        initialEdges =
+            [ Graphviz.Edge
+                { Graphviz.edgeFrom = "init"
+                , Graphviz.edgeTo = show do fromEnum sn
+                , Graphviz.edgeLabel = Nothing
+                }
+            | (_, sn) <- EnumMap.assocs do DFA.dfaInitials dfa
+            ]
+
+        edges sn dst =
+            let builder =
+                    do case DFA.dstOtherTrans dst of
+                        Nothing -> mempty
+                        Just ot -> edgeBuilder sn -1 ot
+                    <> foldMap
+                        do \(lb, to) -> edgeBuilder sn lb to
+                        do IntMap.assocs do DFA.dstTrans dst
+            in
+                [ edge fr lb to
+                | ((fr, to), lb) <- HashMap.toList do unEdgeBuilder builder
+                ]
+
+        edge :: MState.StateNum -> IntSet.IntSet -> MState.StateNum -> Graphviz.Edge
+        edge fr lb to = Graphviz.Edge
+            { Graphviz.edgeFrom = show do fromEnum fr
+            , Graphviz.edgeTo = show do fromEnum to
+            , Graphviz.edgeLabel = edgeLabel lb
+            }
+
+edgeLabel :: IntSet.IntSet -> Maybe Prelude.String
+edgeLabel xs0 = case IntSet.toAscList xs0 of
+    []    -> Nothing
+    x0:xs ->
+        let endPrevRange (s, p, b) = case b of
+                True  -> s
+                False -> s . ("-" ++) . (show p ++)
+            s0 = endPrevRange
+                do foldl'
+                    do \ctx@(!s, !p, _) x -> if
+                        | x == p + 1 -> (s, x, False)
+                        | otherwise  ->
+                            ( endPrevRange ctx . ("," ++) . (show x ++)
+                            , x
+                            , True
+                            )
+                    do ((show x0 ++), x0, True)
+                    do xs
+        in Just do "[" ++ s0 "]"
+
diff --git a/src/Language/Lexer/Tlex/Plugin/Debug/Graphviz.hs b/src/Language/Lexer/Tlex/Plugin/Debug/Graphviz.hs
new file mode 100644
--- /dev/null
+++ b/src/Language/Lexer/Tlex/Plugin/Debug/Graphviz.hs
@@ -0,0 +1,80 @@
+module Language.Lexer.Tlex.Plugin.Debug.Graphviz (
+    NodeShape (..),
+    Node (..),
+    Edge (..),
+    Ast (..),
+    outputAst,
+) where
+
+import           Language.Lexer.Tlex.Prelude
+
+import qualified Prelude
+
+
+data NodeShape
+    = DoubleCircle
+    | Circle
+    deriving (Eq, Show, Ord, Enum)
+
+type NodeId = Prelude.String
+
+data Node = Node
+    { nodeId    :: NodeId
+    , nodeLabel :: Maybe Prelude.String
+    , nodeShape :: Maybe NodeShape
+    }
+    deriving (Eq, Show)
+
+data Edge = Edge
+    { edgeFrom  :: NodeId
+    , edgeTo    :: NodeId
+    , edgeLabel :: Maybe Prelude.String
+    }
+    deriving (Eq, Show)
+
+data Ast = Ast
+    { nodes :: [Node]
+    , edges :: [Edge]
+    }
+    deriving (Eq, Show)
+
+outputAst :: Ast -> Prelude.String
+outputAst ast =
+    "digraph {\n" ++
+    nodeDef ++
+    edgeDef ++
+    "}"
+    where
+        nodeDef = concatMap
+            do \n ->
+                nodeId n ++
+                " [" ++
+                do case nodeLabel n of
+                    Just lb -> "label = \"" ++ lb ++ "\","
+                    Nothing -> ""
+                ++
+                do case nodeShape n of
+                    Nothing -> ""
+                    Just sh ->
+                        "shape = " ++
+                        do case sh of
+                            DoubleCircle -> "doublecircle"
+                            Circle       -> "circle"
+                        ++
+                        ","
+                ++
+                "];\n"
+            do nodes ast
+
+        edgeDef = concatMap
+            do \e ->
+                edgeFrom e ++
+                " -> " ++
+                edgeTo e ++
+                " [" ++
+                do case edgeLabel e of
+                    Just lb -> "label = \"" ++ lb ++ "\","
+                    Nothing -> ""
+                ++
+                "];\n"
+            do edges ast
diff --git a/test/doctest/Doctest.hs b/test/doctest/Doctest.hs
new file mode 100644
--- /dev/null
+++ b/test/doctest/Doctest.hs
@@ -0,0 +1,21 @@
+module Main where
+
+import           Prelude
+
+import qualified Build_doctests     as BuildF
+import           Control.Monad
+import qualified System.Environment as IO
+import qualified System.IO          as IO
+import           Test.DocTest       (doctest)
+
+main :: IO ()
+main = forM_ BuildF.components \(BuildF.Component name flags pkgs sources) -> do
+  putStrLn "============================================="
+  print name
+  putStrLn "---------------------------------------------"
+  IO.hFlush IO.stdout
+  let args = flags ++ pkgs ++ sources
+  IO.unsetEnv "GHC_ENVIRONMENT"
+  doctest args
+  putStrLn "============================================="
+  IO.hFlush IO.stdout
diff --git a/test/spec/HSpecDriver.hs b/test/spec/HSpecDriver.hs
new file mode 100644
--- /dev/null
+++ b/test/spec/HSpecDriver.hs
@@ -0,0 +1,1 @@
+{-# OPTIONS_GHC -F -pgmF hspec-discover #-}
diff --git a/tlex-debug.cabal b/tlex-debug.cabal
new file mode 100644
--- /dev/null
+++ b/tlex-debug.cabal
@@ -0,0 +1,154 @@
+cabal-version:       3.0
+build-type:          Custom
+
+name:                tlex-debug
+version:             0.1.0.0
+license:             Apache-2.0 OR MPL-2.0
+license-file:        LICENSE
+copyright:           (c) 2021 Mizunashi Mana
+author:              Mizunashi Mana
+maintainer:          mizunashi-mana@noreply.git
+
+category:            Parsing
+homepage:            https://github.com/mizunashi-mana/tlex
+bug-reports:         https://github.com/mizunashi-mana/tlex/issues
+synopsis:            Debug utilities for Tlex
+description:
+    Tlex is haskell libraries and toolchains for generating lexical analyzer.
+    See also: https://github.com/mizunashi-mana/tlex
+
+extra-source-files:
+    README.md
+    CHANGELOG.md
+
+source-repository head
+  type:     git
+  location: https://github.com/mizunashi-mana/tlex.git
+
+flag develop
+    default:     False
+    manual:      True
+    description: Turn on some options for development
+
+common general
+    default-language:
+        Haskell2010
+    default-extensions:
+        NoImplicitPrelude
+        BangPatterns
+        BinaryLiterals
+        BlockArguments
+        ConstraintKinds
+        DataKinds
+        DefaultSignatures
+        DeriveFoldable
+        DeriveFunctor
+        DeriveGeneric
+        DeriveLift
+        DeriveTraversable
+        DerivingVia
+        DuplicateRecordFields
+        EmptyCase
+        FlexibleContexts
+        FlexibleInstances
+        FunctionalDependencies
+        GADTs
+        InstanceSigs
+        LambdaCase
+        MagicHash
+        MultiParamTypeClasses
+        MultiWayIf
+        NamedFieldPuns
+        NegativeLiterals
+        NumericUnderscores
+        OverloadedLabels
+        PackageImports
+        PatternSynonyms
+        PolyKinds
+        RankNTypes
+        ScopedTypeVariables
+        StandaloneDeriving
+        Strict
+        TypeApplications
+        TypeFamilies
+        TypeOperators
+        UnboxedSums
+        UnboxedTuples
+
+    if flag(develop)
+        ghc-options:
+            -Wall
+            -Wcompat
+            -Wincomplete-uni-patterns
+            -Wmonomorphism-restriction
+            -Wpartial-fields
+
+            -fprint-explicit-foralls
+            -frefinement-level-hole-fits=1
+
+            -dcore-lint
+
+    build-depends:
+        base                 >= 4.12.0 && < 4.15,
+
+        -- project depends
+        tlex-core            >= 0.1.0 && < 0.2,
+        tlex                 >= 0.1.0 && < 0.2,
+        containers           >= 0.6.0 && < 0.7,
+        unordered-containers >= 0.2.13 && < 0.3,
+
+    autogen-modules:
+        Paths_tlex_debug
+    other-modules:
+        Paths_tlex_debug
+
+custom-setup
+    setup-depends:
+        base,
+        Cabal,
+        cabal-doctest,
+
+library
+    import:
+        general,
+    hs-source-dirs:
+        src
+    exposed-modules:
+        Language.Lexer.Tlex.Plugin.Debug
+        Language.Lexer.Tlex.Plugin.Debug.Graphviz
+
+test-suite doctest
+    import:
+        general,
+    type:
+        exitcode-stdio-1.0
+    hs-source-dirs:
+        test/doctest
+    main-is:
+        Doctest.hs
+    build-depends:
+        doctest,
+        QuickCheck,
+    autogen-modules:
+        Build_doctests
+    other-modules:
+        Build_doctests
+
+test-suite spec
+    import:
+        general,
+    type:
+        exitcode-stdio-1.0
+    hs-source-dirs:
+        test/spec
+    main-is:
+        HSpecDriver.hs
+    ghc-options:
+        -Wno-missing-home-modules
+    build-tool-depends:
+        hspec-discover:hspec-discover,
+    build-depends:
+        tlex-debug,
+
+        hspec,
+        QuickCheck,