diff --git a/LICENSE b/LICENSE
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+++ b/LICENSE
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+                    GNU AFFERO GENERAL PUBLIC LICENSE
+                       Version 3, 19 November 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
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+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Affero General Public License as published
+    by the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Affero General Public License for more details.
+
+    You should have received a copy of the GNU Affero General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If your software can interact with users remotely through a computer
+network, you should also make sure that it provides a way for users to
+get its source.  For example, if your program is a web application, its
+interface could display a "Source" link that leads users to an archive
+of the code.  There are many ways you could offer source, and different
+solutions will be better for different programs; see section 13 for the
+specific requirements.
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU AGPL, see
+<https://www.gnu.org/licenses/>.
diff --git a/README.md b/README.md
new file mode 100644
--- /dev/null
+++ b/README.md
@@ -0,0 +1,22 @@
+# forex2ledger
+
+This tool prints currency exchange rates in [plain text account
+format](https://plaintextaccounting.org/), e.g.;
+
+```
+$ stack run -- --config_file config-sample.toml
+P 2021-03-21 USD 0.929777 CHF
+P 2021-03-21 USD 0.836925 EUR
+```
+
+## Installation
+
+Run `stack install`. This command installs the `forex2ledger` binary in your
+`PATH`.
+
+## Usage
+
+You will need a valid app ID from http://openexchangerates.org.
+
+1. Add a valid app ID to `config-sample.toml`.
+2. Run `stack run -- --config_file config-sample.toml`.
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,3 @@
+import Distribution.Simple
+
+main = defaultMain
diff --git a/app/Main.hs b/app/Main.hs
new file mode 100644
--- /dev/null
+++ b/app/Main.hs
@@ -0,0 +1,68 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Main (main) where
+
+import Config (
+  Config (..),
+  parseConfig,
+ )
+import qualified Data.Text.IO as T
+import Ledger (ratesToLedger)
+import OpenExchangeRates (fetchRates)
+import Options.Applicative (
+  Parser,
+  execParser,
+  fullDesc,
+  header,
+  help,
+  helper,
+  info,
+  long,
+  metavar,
+  progDesc,
+  strOption,
+ )
+import Relude
+
+newtype ConfigFilePath = ConfigFilePath FilePath
+  deriving newtype (Show, Eq)
+
+configFilePathP :: Parser ConfigFilePath
+configFilePathP =
+  ConfigFilePath
+    <$> strOption
+      ( long "config_file"
+          <> metavar "FILE"
+          <> help "The TOML config file."
+      )
+
+run :: ConfigFilePath -> IO ()
+run (ConfigFilePath configFilePath) = do
+  eitherConfig <- parseConfig <$> T.readFile configFilePath
+  case eitherConfig of
+    Left err -> do
+      T.hPutStrLn stderr "Could not parse the config file."
+      T.hPutStrLn stderr err
+      exitFailure
+    Right config@(Config _appId base _) -> do
+      oerResult <- fetchRates config
+      case oerResult of
+        Left err -> do
+          T.hPutStrLn stderr "Could not fetch rates from OER."
+          T.hPutStrLn stderr err
+          exitFailure
+        Right rates -> do
+          T.putStr $ ratesToLedger base rates
+
+main :: IO ()
+main = do
+  configFilePath <- execParser opts
+  run configFilePath
+ where
+  opts =
+    info
+      (configFilePathP <**> helper)
+      ( fullDesc
+          <> progDesc "Print Forex rates in Ledger format."
+          <> header "forex2ledger"
+      )
diff --git a/forex2ledger.cabal b/forex2ledger.cabal
new file mode 100644
--- /dev/null
+++ b/forex2ledger.cabal
@@ -0,0 +1,94 @@
+cabal-version: 1.12
+
+-- This file has been generated from package.yaml by hpack version 0.34.4.
+--
+-- see: https://github.com/sol/hpack
+
+name:           forex2ledger
+version:        1.0.0.0
+synopsis:       Print Forex quotes in Ledger format
+description:    Please see the README on GitHub at <https://github.com/gregorias/forex2ledger#readme>
+category:       Finance
+homepage:       https://github.com/gregorias/forex2ledger#readme
+bug-reports:    https://github.com/gregorias/forex2ledger/issues
+author:         Grzegorz Milka
+maintainer:     grzegorzmilka@gmail.com
+copyright:      Copyright (c) 2021 Grzegorz Milka
+license:        AGPL-3
+license-file:   LICENSE
+build-type:     Simple
+extra-source-files:
+    README.md
+
+source-repository head
+  type: git
+  location: https://github.com/gregorias/forex2ledger
+
+library
+  exposed-modules:
+      AppId
+      Config
+      Ledger
+      OpenExchangeRates
+  other-modules:
+      Paths_forex2ledger
+  hs-source-dirs:
+      src
+  default-extensions:
+      DerivingStrategies GeneralisedNewtypeDeriving InstanceSigs LambdaCase NoImplicitPrelude NumericUnderscores ScopedTypeVariables TupleSections TypeApplications UnicodeSyntax
+  build-depends:
+      HTTP
+    , aeson
+    , base >=4.13 && <5
+    , containers
+    , currency-codes
+    , hledger-lib >=1.21
+    , relude
+    , text
+    , time
+    , tomland
+    , unordered-containers
+    , url
+  default-language: Haskell2010
+
+executable forex2ledger
+  main-is: Main.hs
+  other-modules:
+      Paths_forex2ledger
+  hs-source-dirs:
+      app
+  default-extensions:
+      DerivingStrategies GeneralisedNewtypeDeriving InstanceSigs LambdaCase NoImplicitPrelude NumericUnderscores ScopedTypeVariables TupleSections TypeApplications UnicodeSyntax
+  ghc-options: -threaded -rtsopts -with-rtsopts=-N
+  build-depends:
+      base >=4.13 && <5
+    , forex2ledger
+    , optparse-applicative
+    , relude
+    , text
+  default-language: Haskell2010
+
+test-suite forex2ledger-test
+  type: exitcode-stdio-1.0
+  main-is: Spec.hs
+  other-modules:
+      Test.Config
+      Test.Ledger
+      Test.OpenExchangeRates
+      Paths_forex2ledger
+  hs-source-dirs:
+      test
+  default-extensions:
+      DerivingStrategies GeneralisedNewtypeDeriving InstanceSigs LambdaCase NoImplicitPrelude NumericUnderscores ScopedTypeVariables TupleSections TypeApplications UnicodeSyntax
+  ghc-options: -threaded -rtsopts -with-rtsopts=-N -main-is Spec
+  build-depends:
+      aeson
+    , base >=4.13 && <5
+    , containers
+    , currency-codes
+    , forex2ledger
+    , hspec
+    , hspec-expectations-pretty-diff
+    , relude
+    , time
+  default-language: Haskell2010
diff --git a/src/AppId.hs b/src/AppId.hs
new file mode 100644
--- /dev/null
+++ b/src/AppId.hs
@@ -0,0 +1,16 @@
+module AppId (
+  AppId (..),
+) where
+
+import Relude (
+  Eq,
+  IsString,
+  Read,
+  Show,
+  Text,
+ )
+
+newtype AppId = AppId
+  { unAppId :: Text
+  }
+  deriving newtype (Read, Show, Eq, IsString)
diff --git a/src/Config.hs b/src/Config.hs
new file mode 100644
--- /dev/null
+++ b/src/Config.hs
@@ -0,0 +1,36 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+-- | This module parses the config file.
+module Config (
+  Config (..),
+  parseConfig,
+) where
+
+import AppId (AppId (..))
+import Data.Currency (Alpha)
+import Relude
+import Toml (TomlBiMap, TomlCodec, prettyTomlDecodeErrors, (.=))
+import qualified Toml
+
+data Config = Config
+  { configOpenExchangeRateAppId :: !AppId
+  , configBaseCurrency :: !Alpha
+  , configTargetCurrencies :: [Alpha]
+  }
+  deriving stock (Show, Eq)
+
+alphaBiMap :: TomlBiMap Data.Currency.Alpha Toml.AnyValue
+alphaBiMap = Toml._EnumBounded
+
+currencyBiMap :: TomlBiMap Alpha Toml.AnyValue
+currencyBiMap = alphaBiMap
+
+configCodec :: TomlCodec Config
+configCodec =
+  Config
+    <$> Toml.diwrap (Toml.text "oer_app_id") .= configOpenExchangeRateAppId
+    <*> Toml.match currencyBiMap "currency.base" .= configBaseCurrency
+    <*> Toml.arrayOf currencyBiMap "currency.targets" .= configTargetCurrencies
+
+parseConfig :: Text -> Either Text Config
+parseConfig = first prettyTomlDecodeErrors . Toml.decode configCodec
diff --git a/src/Ledger.hs b/src/Ledger.hs
new file mode 100644
--- /dev/null
+++ b/src/Ledger.hs
@@ -0,0 +1,67 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Ledger (
+  ratesToLedger,
+) where
+
+import Data.Currency (Alpha)
+import Data.Fixed (E6, Fixed)
+import qualified Data.Map.Strict as Map
+import qualified Data.Text as T
+import Data.Time (Day)
+import Data.Time.Format.ISO8601 (
+  FormatExtension (ExtendedFormat),
+  calendarFormat,
+  formatShow,
+ )
+import Hledger (MarketPrice (MarketPrice))
+import OpenExchangeRates (OerRates (..))
+import Relude
+import Text.Printf (printf)
+
+-- | Renders MarketPrice as Ledger-style text
+--
+-- @
+-- P yyyy-mm-dd from price to
+-- @
+showMarketPrice :: MarketPrice -> Text
+showMarketPrice (MarketPrice day from to price) =
+  T.pack $
+    printf
+      "P %s %s %s %s\n"
+      (formatShow (calendarFormat ExtendedFormat) day)
+      from
+      (show price :: Text)
+      to
+
+rateToMarketPrice ::
+  Day ->
+  -- | the base currency
+  Alpha ->
+  -- | the quote currency
+  Alpha ->
+  -- | the price
+  Fixed E6 ->
+  MarketPrice
+rateToMarketPrice day base target price =
+  MarketPrice
+    day
+    (show base)
+    (show target)
+    (fromRational . toRational $ price)
+
+ratesToMarketPrices ::
+  -- | the base currency
+  Alpha ->
+  OerRates ->
+  [MarketPrice]
+ratesToMarketPrices base (OerRates day rates) =
+  map (uncurry (rateToMarketPrice day base)) $ Map.toList rates
+
+ratesToLedger ::
+  -- | the base currency
+  Alpha ->
+  OerRates ->
+  Text
+ratesToLedger base =
+  T.concat . map showMarketPrice . ratesToMarketPrices base
diff --git a/src/OpenExchangeRates.hs b/src/OpenExchangeRates.hs
new file mode 100644
--- /dev/null
+++ b/src/OpenExchangeRates.hs
@@ -0,0 +1,107 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+-- | This module fetches rates from openexchangerates.org
+module OpenExchangeRates (
+  fetchRates,
+  OerRates (..),
+) where
+
+import AppId (AppId (AppId))
+import Config (Config (Config))
+import qualified Data.Aeson as Aeson
+import Data.Currency (Alpha)
+import Data.Fixed (E6, Fixed)
+import qualified Data.HashMap.Strict as HashMap
+import qualified Data.Text as T
+import Data.Time (Day, UTCTime (utctDay), secondsToNominalDiffTime)
+import Data.Time.Clock.POSIX (posixSecondsToUTCTime)
+import qualified Network.HTTP as HTTP
+import Network.URL (
+  URL (
+    URL,
+    url_params,
+    url_path,
+    url_type
+  ),
+  exportURL,
+ )
+import qualified Network.URL as URL
+import Relude
+
+type CurrencyResolution = E6
+
+data OerRates = OerRates
+  { orTimestamp :: !Day
+  , orRates :: Map Alpha (Fixed CurrencyResolution)
+  }
+  deriving stock (Show, Eq)
+
+alphaP :: Text -> Either Text Alpha
+alphaP currencyTxt =
+  maybeToRight ("Could not parse " `T.append` currencyTxt `T.append` " as currency.\n")
+    . readMaybe
+    . T.unpack
+    $ currencyTxt
+
+currencyInKeysP :: HashMap Text (Fixed CurrencyResolution) -> Either Text (Map Alpha (Fixed CurrencyResolution))
+currencyInKeysP =
+  convertToMap
+    . mapM convertKey
+    . HashMap.toList
+ where
+  convertKey :: (Text, Fixed CurrencyResolution) -> Either Text (Alpha, Fixed CurrencyResolution)
+  convertKey = fmap swap . sequence . swap . first alphaP
+  convertToMap :: Either Text [(Alpha, Fixed CurrencyResolution)] -> Either Text (Map Alpha (Fixed CurrencyResolution))
+  convertToMap = fmap fromList
+
+instance Aeson.FromJSON OerRates where
+  parseJSON (Aeson.Object o) =
+    OerRates
+      <$> timestampP
+      <*> ratesP
+   where
+    timestampP =
+      o Aeson..: "timestamp"
+        & fmap
+          ( utctDay
+              . posixSecondsToUTCTime
+              . secondsToNominalDiffTime
+              . fromInteger
+          )
+    ratesP = do
+      hashMap <- o Aeson..: "rates"
+      let eitherRates = currencyInKeysP hashMap
+      either (fail . T.unpack) return eitherRates
+  parseJSON _ = fail "OpenExchangeRates data should be an object but received something else."
+
+getLatestUrl :: Config -> URL
+getLatestUrl (Config (AppId appId) base targets) =
+  URL
+    { url_type = URL.Absolute (URL.Host (URL.HTTP False) "openexchangerates.org" Nothing)
+    , url_path = "/api/latest.json"
+    , url_params =
+        [ ("app_id", toString appId)
+        , ("base", cur2string base)
+        , ("symbols", intercalate "," (cur2string <$> targets))
+        ]
+    }
+ where
+  cur2string = show
+
+-- | Fetches rates from openexchangerates.org
+fetchRates :: Config -> IO (Either Text OerRates)
+fetchRates config = do
+  response <- HTTP.simpleHTTP req
+  responseCode <- HTTP.getResponseCode response
+  body <- HTTP.getResponseBody response
+  case responseCode of
+    (2, 0, 0) -> do
+      return . first T.pack $ Aeson.eitherDecode (fromString body)
+    _ ->
+      return . Left $
+        "Received a non-200 response code:"
+          `T.append` T.pack (show responseCode)
+          `T.append` " with the response: "
+          `T.append` T.pack body
+ where
+  req = HTTP.getRequest . exportURL . getLatestUrl $ config
diff --git a/test/Spec.hs b/test/Spec.hs
new file mode 100644
--- /dev/null
+++ b/test/Spec.hs
@@ -0,0 +1,19 @@
+module Spec (main) where
+
+import Relude
+import qualified Test.Config as Config
+import Test.Hspec (
+  SpecWith,
+  hspec,
+ )
+import qualified Test.Ledger as Ledger
+import qualified Test.OpenExchangeRates as OpenExchangeRates
+
+main :: IO ()
+main = hspec tests
+
+tests :: SpecWith ()
+tests = do
+  Config.tests
+  Ledger.tests
+  OpenExchangeRates.tests
diff --git a/test/Test/Config.hs b/test/Test/Config.hs
new file mode 100644
--- /dev/null
+++ b/test/Test/Config.hs
@@ -0,0 +1,38 @@
+{-# LANGUAGE OverloadedStrings #-}
+{-# OPTIONS_GHC -Wno-deferred-out-of-scope-variables #-}
+{-# OPTIONS_GHC -Wno-deprecations #-}
+
+module Test.Config (
+  tests,
+) where
+
+import Config (
+  Config (..),
+  parseConfig,
+ )
+import Data.Currency (Alpha (..))
+import Relude
+import Test.Hspec (
+  SpecWith,
+  describe,
+  it,
+  runIO,
+ )
+import Test.Hspec.Expectations.Pretty (shouldBe)
+
+tests :: SpecWith ()
+tests = do
+  describe "Config.parseConfig" $ do
+    describe "parseConfig" $ do
+      sampleConfigText <- runIO (readFileText "config-sample.toml")
+      it "parsesTheSampleConfig" $ do
+        let config = parseConfig sampleConfigText
+        config
+          `shouldBe` Right
+            ( Config
+                "SAMPLEAPPID"
+                USD
+                [ CHF
+                , EUR
+                ]
+            )
diff --git a/test/Test/Ledger.hs b/test/Test/Ledger.hs
new file mode 100644
--- /dev/null
+++ b/test/Test/Ledger.hs
@@ -0,0 +1,33 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Test.Ledger (
+  tests,
+) where
+
+import Data.Currency (Alpha (..))
+import qualified Data.Map.Strict as Map
+import Data.Time (fromGregorian)
+import Ledger (ratesToLedger)
+import OpenExchangeRates (OerRates (OerRates))
+import Relude
+import Test.Hspec (
+  SpecWith,
+  describe,
+  it,
+ )
+import Test.Hspec.Expectations.Pretty (shouldBe)
+
+tests :: SpecWith ()
+tests = describe "Ledger" $ do
+  describe "ratesToLedger" $ do
+    it "formatsRates" $ do
+      ratesToLedger
+        USD
+        ( OerRates
+            (fromGregorian 2021 3 17)
+            ( Map.singleton CHF 0.922272
+                <> Map.singleton EUR 1.1
+            )
+        )
+        `shouldBe` "P 2021-03-17 USD 0.922272 CHF\n\
+                   \P 2021-03-17 USD 1.1 EUR\n"
diff --git a/test/Test/OpenExchangeRates.hs b/test/Test/OpenExchangeRates.hs
new file mode 100644
--- /dev/null
+++ b/test/Test/OpenExchangeRates.hs
@@ -0,0 +1,40 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Test.OpenExchangeRates (
+  tests,
+) where
+
+import qualified Data.Aeson as Aeson
+import Data.Currency (Alpha (..))
+import qualified Data.Map.Strict as Map
+import Data.Time (fromGregorian)
+import OpenExchangeRates (OerRates (OerRates))
+import Relude
+import Test.Hspec (
+  SpecWith,
+  describe,
+  it,
+ )
+import Test.Hspec.Expectations.Pretty (shouldBe)
+
+tests :: SpecWith ()
+tests = describe "OpenExchangeRates" $ do
+  describe "OerRates" $ do
+    describe "Aeson.FromJSON" $ do
+      it "parsesTheSampleConfig" $ do
+        let json =
+              "{\n\
+              \   \"disclaimer\": \"Usage subject to terms: https://openexchangerates.org/terms\",\n\
+              \   \"license\": \"https://openexchangerates.org/license\",\n\
+              \   \"timestamp\": 1616007600,\n\
+              \   \"base\": \"USD\",\n\
+              \   \"rates\": {\n\
+              \     \"CHF\": 0.922272\n\
+              \   }\n\
+              \ }"
+        Aeson.eitherDecode json
+          `shouldBe` Right
+            ( OerRates
+                (fromGregorian 2021 3 17)
+                (Map.singleton CHF 0.922272)
+            )