diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,15 @@
+ISC License
+
+Copyright (c) 2022 Gautier DI FOLCO
+
+Permission to use, copy, modify, and/or distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+PERFORMANCE OF THIS SOFTWARE.
diff --git a/sized-wrapper-aeson.cabal b/sized-wrapper-aeson.cabal
new file mode 100644
--- /dev/null
+++ b/sized-wrapper-aeson.cabal
@@ -0,0 +1,91 @@
+cabal-version:       3.0
+name:                sized-wrapper-aeson
+version:             0.1.0.0
+author:              Gautier DI FOLCO
+maintainer:          gautier.difolco@gmail.com
+category:            Data
+build-type:          Simple
+license:             ISC
+license-file:        LICENSE
+synopsis:            aeson instances for 'Sized'
+description:         aeson instances for 'Sized'.
+Homepage:            http://github.com/blackheaven/sized-wrapper/sized-wrapper-aeson
+tested-with:         GHC==9.2.2, GHC==9.0.2, GHC==8.10.7
+
+library
+  default-language:   Haskell2010
+  build-depends:
+        base == 4.*
+      , aeson == 2.*
+      , sized-wrapper >= 0.1.0.0 && < 1
+  hs-source-dirs: src
+  exposed-modules:
+      Data.Aeson.Types.Instances.Sized
+  other-modules:
+      Paths_sized_wrapper_aeson
+  autogen-modules:
+      Paths_sized_wrapper_aeson
+  default-extensions:
+      DataKinds
+      DefaultSignatures
+      DeriveAnyClass
+      DeriveGeneric
+      DerivingStrategies
+      DerivingVia
+      DuplicateRecordFields
+      FlexibleContexts
+      GADTs
+      GeneralizedNewtypeDeriving
+      KindSignatures
+      LambdaCase
+      OverloadedLists
+      OverloadedStrings
+      RankNTypes
+      RecordWildCards
+      ScopedTypeVariables
+      TypeApplications
+      TypeFamilies
+      TypeOperators
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wpartial-fields -Wredundant-constraints
+
+test-suite sized-wrapper-aeson-test
+  type: exitcode-stdio-1.0
+  hs-source-dirs: test
+  main-is: Spec.hs
+  other-modules:
+      Data.Aeson.Types.Instances.SizedSpec
+      Paths_sized_wrapper_aeson
+  autogen-modules:
+      Paths_sized_wrapper_aeson
+  default-extensions:
+      DataKinds
+      DefaultSignatures
+      DeriveAnyClass
+      DeriveGeneric
+      DerivingStrategies
+      DerivingVia
+      DuplicateRecordFields
+      FlexibleContexts
+      GADTs
+      GeneralizedNewtypeDeriving
+      KindSignatures
+      LambdaCase
+      OverloadedLists
+      OverloadedStrings
+      RankNTypes
+      RecordWildCards
+      ScopedTypeVariables
+      TypeApplications
+      TypeFamilies
+      TypeOperators
+  ghc-options: -threaded -rtsopts -with-rtsopts=-N -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wpartial-fields -Wredundant-constraints
+  build-depends:
+      base
+    , sized-wrapper
+    , sized-wrapper-aeson
+    , aeson
+    , containers >= 0.5 && < 1
+    , hspec
+    , hspec-core
+    , hspec-discover
+  default-language: Haskell2010
diff --git a/src/Data/Aeson/Types/Instances/Sized.hs b/src/Data/Aeson/Types/Instances/Sized.hs
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--- /dev/null
+++ b/src/Data/Aeson/Types/Instances/Sized.hs
@@ -0,0 +1,77 @@
+{-# LANGUAGE UndecidableInstances #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+-- |
+-- Module        : Test.QuickCheck.Instances.Sized
+-- Copyright     : Gautier DI FOLCO
+-- License       : BSD2
+--
+-- Maintainer    : Gautier DI FOLCO <gautier.difolco@gmail.com>
+-- Stability     : Unstable
+-- Portability   : GHC
+--
+-- aeson instances for 'Sized'
+module Data.Aeson.Types.Instances.Sized
+  ( FromJSON (..),
+    ToJSON (..),
+    FromJSONKey (..),
+    ToJSONKey (..),
+  )
+where
+
+import Control.Monad ((>=>))
+import Data.Aeson
+import Data.Aeson.Types
+import Data.Coerce
+import Data.Sized
+
+instance
+  ( FromJSON a,
+    Semigroup a,
+    Size s,
+    SizedSingleton a,
+    SizedFromContainer a,
+    FromJSON (SizedSingletonElement a)
+  ) =>
+  FromJSON (Sized s a)
+  where
+  parseJSON x = do
+    raw <- parseJSON x
+    case sized raw of
+      Just y -> pure y
+      Nothing -> fail "parsing Sized failed, unexpected empty container"
+
+instance
+  ( FromJSON a,
+    Size s,
+    SizedSingleton a,
+    SizedFromContainer a,
+    FromJSON (SizedSingletonElement a),
+    FromJSONKey (SizedSingletonElement a),
+    FromJSONKey a,
+    Semigroup a
+  ) =>
+  FromJSONKey (Sized s a)
+  where
+  fromJSONKey =
+    case fromJSONKey @a of
+      FromJSONKeyCoerce -> FromJSONKeyTextParser (run . coerce)
+      FromJSONKeyText f -> FromJSONKeyTextParser (run . f)
+      FromJSONKeyTextParser f -> FromJSONKeyTextParser (f >=> run)
+      FromJSONKeyValue f -> FromJSONKeyValue (f >=> run)
+    where
+      run :: a -> Parser (Sized s a)
+      run x =
+        case sized x of
+          Just y -> pure y
+          Nothing -> fail "parsing Sized failed, unexpected empty container"
+
+instance (ToJSON a) => ToJSON (Sized s a) where
+  toJSON = toJSON . getSized
+  toEncoding = toEncoding . getSized
+  toJSONList = toJSONList . map getSized
+  toEncodingList = toEncodingList . map getSized
+
+instance (ToJSONKey a) => ToJSONKey (Sized s a) where
+  toJSONKey = contramapToJSONKeyFunction getSized toJSONKey
+  toJSONKeyList = contramapToJSONKeyFunction (map getSized) toJSONKeyList
diff --git a/test/Data/Aeson/Types/Instances/SizedSpec.hs b/test/Data/Aeson/Types/Instances/SizedSpec.hs
new file mode 100644
--- /dev/null
+++ b/test/Data/Aeson/Types/Instances/SizedSpec.hs
@@ -0,0 +1,35 @@
+module Data.Aeson.Types.Instances.SizedSpec
+  ( main,
+    spec,
+  )
+where
+
+import Data.Aeson
+import Data.Aeson.Types.Instances.Sized ()
+import qualified Data.Map.Strict as M
+import Data.Proxy
+import Data.Sized
+import Test.Hspec
+
+main :: IO ()
+main = hspec spec
+
+spec :: Spec
+spec = do
+  describe "decode" $ do
+    describe "regular element" $ do
+      it "valid case should parse" $
+        decode "[42]" `shouldBe` Just (singleton (Proxy @[Int]) 42)
+      it "empty case should fail" $
+        decode "[]" `shouldBe` Nothing @(Sized (Exactly 4) String)
+    describe "key" $ do
+      it "valid case should parse" $
+        decode "{\"a\":42}" `shouldBe` Just (M.singleton (singleton (Proxy @String) 'a') (42 :: Int))
+      it "empty case should fail" $
+        decode "{\"\":42}" `shouldBe` Nothing @(M.Map (Sized (Exactly 4) String) Int)
+
+  describe "encode" $ do
+    it "list of Int" $
+      encode (singleton (Proxy @[Int]) 42) `shouldBe` "[42]"
+    it "keymap" $
+      encode (M.singleton (singleton (Proxy @String) 'a') (42 :: Int)) `shouldBe` "{\"a\":42}"
diff --git a/test/Spec.hs b/test/Spec.hs
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--- /dev/null
+++ b/test/Spec.hs
@@ -0,0 +1,1 @@
+{-# OPTIONS_GHC -F -pgmF hspec-discover #-}