diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,30 @@
+Copyright (c) 2019, Andrew Martin
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * 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.
+
+    * Neither the name of Andrew Martin nor the names of other
+      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
+OWNER 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
new file mode 100644
--- /dev/null
+++ b/README.md
@@ -0,0 +1,4 @@
+# error-codes
+
+A library for converting printing human-readable descriptions of error codes
+from the operating system.
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/error-codes.cabal b/error-codes.cabal
new file mode 100644
--- /dev/null
+++ b/error-codes.cabal
@@ -0,0 +1,33 @@
+cabal-version: 2.2
+name: error-codes
+version: 0.1.0.0
+synopsis: Error code functions
+homepage: https://github.com/andrewthad/error-codes
+bug-reports: https://github.com/andrewthad/error-codes/issues
+license: BSD-3-Clause
+license-file: LICENSE
+author: Andrew Martin
+maintainer: andrew.thaddeus@gmail.com
+copyright: 2019 Andrew Martin
+category: System
+extra-source-files: README.md
+
+library
+  exposed-modules:
+    Foreign.C.Error.Describe
+  build-depends:
+    , base >=4.11.1.0 && <5
+    , primitive >=0.6.4
+  hs-source-dirs: src
+  default-language: Haskell2010
+  ghc-options: -Wall -O2
+
+test-suite test
+  type: exitcode-stdio-1.0
+  hs-source-dirs: test
+  main-is: Main.hs
+  build-depends:
+    , base
+    , error-codes
+  ghc-options: -Wall -O2
+  default-language: Haskell2010
diff --git a/src/Foreign/C/Error/Describe.hs b/src/Foreign/C/Error/Describe.hs
new file mode 100644
--- /dev/null
+++ b/src/Foreign/C/Error/Describe.hs
@@ -0,0 +1,173 @@
+{-# language BangPatterns #-}
+
+module Foreign.C.Error.Describe
+  ( string
+  , byteArray
+  ) where
+
+import Data.Char (ord,chr)
+import Data.Primitive (SmallArray,UnliftedArray,ByteArray(..))
+import Data.Word (Word8)
+import Foreign.C.Types (CInt)
+import Foreign.C.Error (Errno(..))
+import Data.Foldable (for_)
+import Control.Monad.ST (runST)
+import qualified Data.Primitive as PM
+import qualified GHC.Exts as E
+import qualified Foreign.C.Error as ERR
+
+unErrno :: Errno -> CInt
+unErrno (Errno i) = i
+
+
+string :: Errno -> String
+string (Errno i) = if fromIntegral i < (256 :: Word)
+  then asString (PM.indexUnliftedArray table (fromIntegral i))
+  else unknownString
+
+byteArray :: Errno -> ByteArray
+byteArray (Errno i) = if fromIntegral i < (256 :: Word)
+  then PM.indexUnliftedArray table (fromIntegral i)
+  else case unknown of
+    ByteArray b -> ByteArray b
+
+{-# NOINLINE unknown #-}
+unknown :: ByteArray
+unknown = asBytes unknownString
+
+unknownString :: String
+unknownString = "UNKNOWN"
+
+table :: UnliftedArray ByteArray
+table = runST $ do
+  m <- PM.newUnliftedArray 256 (mempty :: ByteArray)
+  for_ codes $ \(Description code descr) -> do
+    let ix = fromIntegral code :: Int
+    if ix < (256 :: Int)
+      then if ix >= 0
+        then PM.writeUnliftedArray m ix descr
+        else pure ()
+      else pure ()
+  PM.unsafeFreezeUnliftedArray m
+
+data Description = Description !CInt !ByteArray
+
+asBytes :: String -> ByteArray
+asBytes s = runST $ do
+  m <- PM.newByteArray (length s)
+  for_ (zip (enumFrom (0 :: Int)) s) $ \(ix,c) -> do
+    PM.writeByteArray m ix (charToWord8 c)
+  PM.unsafeFreezeByteArray m
+
+asString :: ByteArray -> String
+asString = PM.foldrByteArray (\b cs -> word8ToChar b : cs) []
+
+charToWord8 :: Char -> Word8
+charToWord8 = fromIntegral . ord
+
+word8ToChar :: Word8 -> Char
+word8ToChar = chr . fromIntegral
+
+codes :: SmallArray Description
+codes = E.fromList
+  [ Description (unErrno ERR.eOK) (asBytes "EOK")
+  , Description (unErrno ERR.e2BIG) (asBytes "E2BIG")
+  , Description (unErrno ERR.eACCES) (asBytes "EACCES")
+  , Description (unErrno ERR.eADDRINUSE) (asBytes "EADDRINUSE")
+  , Description (unErrno ERR.eADDRNOTAVAIL) (asBytes "EADDRNOTAVAIL")
+  , Description (unErrno ERR.eADV) (asBytes "EADV")
+  , Description (unErrno ERR.eAFNOSUPPORT) (asBytes "EAFNOSUPPORT")
+  , Description (unErrno ERR.eAGAIN) (asBytes "EAGAIN")
+  , Description (unErrno ERR.eALREADY) (asBytes "EALREADY")
+  , Description (unErrno ERR.eBADF) (asBytes "EBADF")
+  , Description (unErrno ERR.eBADMSG) (asBytes "EBADMSG")
+  , Description (unErrno ERR.eBADRPC) (asBytes "EBADRPC")
+  , Description (unErrno ERR.eBUSY) (asBytes "EBUSY")
+  , Description (unErrno ERR.eCHILD) (asBytes "ECHILD")
+  , Description (unErrno ERR.eCOMM) (asBytes "ECOMM")
+  , Description (unErrno ERR.eCONNABORTED) (asBytes "ECONNABORTED")
+  , Description (unErrno ERR.eCONNREFUSED) (asBytes "ECONNREFUSED")
+  , Description (unErrno ERR.eCONNRESET) (asBytes "ECONNRESET")
+  , Description (unErrno ERR.eDEADLK) (asBytes "EDEADLK")
+  , Description (unErrno ERR.eDESTADDRREQ) (asBytes "EDESTADDRREQ")
+  , Description (unErrno ERR.eDIRTY) (asBytes "EDIRTY")
+  , Description (unErrno ERR.eDOM) (asBytes "EDOM")
+  , Description (unErrno ERR.eDQUOT) (asBytes "EDQUOT")
+  , Description (unErrno ERR.eEXIST) (asBytes "EEXIST")
+  , Description (unErrno ERR.eFAULT) (asBytes "EFAULT")
+  , Description (unErrno ERR.eFBIG) (asBytes "EFBIG")
+  , Description (unErrno ERR.eFTYPE) (asBytes "EFTYPE")
+  , Description (unErrno ERR.eHOSTDOWN) (asBytes "EHOSTDOWN")
+  , Description (unErrno ERR.eHOSTUNREACH) (asBytes "EHOSTUNREACH")
+  , Description (unErrno ERR.eIDRM) (asBytes "EIDRM")
+  , Description (unErrno ERR.eILSEQ) (asBytes "EILSEQ")
+  , Description (unErrno ERR.eINPROGRESS) (asBytes "EINPROGRESS")
+  , Description (unErrno ERR.eINTR) (asBytes "EINTR")
+  , Description (unErrno ERR.eINVAL) (asBytes "EINVAL")
+  , Description (unErrno ERR.eIO) (asBytes "EIO")
+  , Description (unErrno ERR.eISCONN) (asBytes "EISCONN")
+  , Description (unErrno ERR.eISDIR) (asBytes "EISDIR")
+  , Description (unErrno ERR.eLOOP) (asBytes "ELOOP")
+  , Description (unErrno ERR.eMFILE) (asBytes "EMFILE")
+  , Description (unErrno ERR.eMLINK) (asBytes "EMLINK")
+  , Description (unErrno ERR.eMSGSIZE) (asBytes "EMSGSIZE")
+  , Description (unErrno ERR.eMULTIHOP) (asBytes "EMULTIHOP")
+  , Description (unErrno ERR.eNAMETOOLONG) (asBytes "ENAMETOOLONG")
+  , Description (unErrno ERR.eNETDOWN) (asBytes "ENETDOWN")
+  , Description (unErrno ERR.eNETRESET) (asBytes "ENETRESET")
+  , Description (unErrno ERR.eNETUNREACH) (asBytes "ENETUNREACH")
+  , Description (unErrno ERR.eNFILE) (asBytes "ENFILE")
+  , Description (unErrno ERR.eNOBUFS) (asBytes "ENOBUFS")
+  , Description (unErrno ERR.eNODATA) (asBytes "ENODATA")
+  , Description (unErrno ERR.eNODEV) (asBytes "ENODEV")
+  , Description (unErrno ERR.eNOENT) (asBytes "ENOENT")
+  , Description (unErrno ERR.eNOEXEC) (asBytes "ENOEXEC")
+  , Description (unErrno ERR.eNOLCK) (asBytes "ENOLCK")
+  , Description (unErrno ERR.eNOLINK) (asBytes "ENOLINK")
+  , Description (unErrno ERR.eNOMEM) (asBytes "ENOMEM")
+  , Description (unErrno ERR.eNOMSG) (asBytes "ENOMSG")
+  , Description (unErrno ERR.eNONET) (asBytes "ENONET")
+  , Description (unErrno ERR.eNOPROTOOPT) (asBytes "ENOPROTOOPT")
+  , Description (unErrno ERR.eNOSPC) (asBytes "ENOSPC")
+  , Description (unErrno ERR.eNOSR) (asBytes "ENOSR")
+  , Description (unErrno ERR.eNOSTR) (asBytes "ENOSTR")
+  , Description (unErrno ERR.eNOSYS) (asBytes "ENOSYS")
+  , Description (unErrno ERR.eNOTBLK) (asBytes "ENOTBLK")
+  , Description (unErrno ERR.eNOTCONN) (asBytes "ENOTCONN")
+  , Description (unErrno ERR.eNOTDIR) (asBytes "ENOTDIR")
+  , Description (unErrno ERR.eNOTEMPTY) (asBytes "ENOTEMPTY")
+  , Description (unErrno ERR.eNOTSOCK) (asBytes "ENOTSOCK")
+  , Description (unErrno ERR.eNOTSUP) (asBytes "ENOTSUP")
+  , Description (unErrno ERR.eNOTTY) (asBytes "ENOTTY")
+  , Description (unErrno ERR.eNXIO) (asBytes "ENXIO")
+  , Description (unErrno ERR.eOPNOTSUPP) (asBytes "EOPNOTSUPP")
+  , Description (unErrno ERR.ePERM) (asBytes "EPERM")
+  , Description (unErrno ERR.ePFNOSUPPORT) (asBytes "EPFNOSUPPORT")
+  , Description (unErrno ERR.ePIPE) (asBytes "EPIPE")
+  , Description (unErrno ERR.ePROCLIM) (asBytes "EPROCLIM")
+  , Description (unErrno ERR.ePROCUNAVAIL) (asBytes "EPROCUNAVAIL")
+  , Description (unErrno ERR.ePROGMISMATCH) (asBytes "EPROGMISMATCH")
+  , Description (unErrno ERR.ePROGUNAVAIL) (asBytes "EPROGUNAVAIL")
+  , Description (unErrno ERR.ePROTO) (asBytes "EPROTO")
+  , Description (unErrno ERR.ePROTONOSUPPORT) (asBytes "EPROTONOSUPPORT")
+  , Description (unErrno ERR.ePROTOTYPE) (asBytes "EPROTOTYPE")
+  , Description (unErrno ERR.eRANGE) (asBytes "ERANGE")
+  , Description (unErrno ERR.eREMCHG) (asBytes "EREMCHG")
+  , Description (unErrno ERR.eREMOTE) (asBytes "EREMOTE")
+  , Description (unErrno ERR.eROFS) (asBytes "EROFS")
+  , Description (unErrno ERR.eRPCMISMATCH) (asBytes "ERPCMISMATCH")
+  , Description (unErrno ERR.eRREMOTE) (asBytes "ERREMOTE")
+  , Description (unErrno ERR.eSHUTDOWN) (asBytes "ESHUTDOWN")
+  , Description (unErrno ERR.eSOCKTNOSUPPORT) (asBytes "ESOCKTNOSUPPORT")
+  , Description (unErrno ERR.eSPIPE) (asBytes "ESPIPE")
+  , Description (unErrno ERR.eSRCH) (asBytes "ESRCH")
+  , Description (unErrno ERR.eSRMNT) (asBytes "ESRMNT")
+  , Description (unErrno ERR.eSTALE) (asBytes "ESTALE")
+  , Description (unErrno ERR.eTIME) (asBytes "ETIME")
+  , Description (unErrno ERR.eTIMEDOUT) (asBytes "ETIMEDOUT")
+  , Description (unErrno ERR.eTOOMANYREFS) (asBytes "ETOOMANYREFS")
+  , Description (unErrno ERR.eTXTBSY) (asBytes "ETXTBSY")
+  , Description (unErrno ERR.eUSERS) (asBytes "EUSERS")
+  , Description (unErrno ERR.eWOULDBLOCK) (asBytes "EWOULDBLOCK")
+  , Description (unErrno ERR.eXDEV) (asBytes "EXDEV")
+  ]
diff --git a/test/Main.hs b/test/Main.hs
new file mode 100644
--- /dev/null
+++ b/test/Main.hs
@@ -0,0 +1,22 @@
+import Control.Monad (when)
+import Foreign.C.Error
+
+import qualified Foreign.C.Error.Describe as D
+
+main :: IO ()
+main = do
+  stringMatch "A" eOK "EOK"
+  stringMatch "B" eADDRNOTAVAIL "EADDRNOTAVAIL"
+  stringMatch "C" eOPNOTSUPP "EOPNOTSUPP"
+  stringMatch "D" (Errno (-5264)) "UNKNOWN"
+  stringMatch "E" (Errno (-1)) "UNKNOWN"
+  stringMatch "F" (Errno 257) "UNKNOWN"
+  putStrLn "All tests passed"
+
+stringMatch :: String -> Errno -> String -> IO ()
+stringMatch ident e expected = do
+  let actual = D.string e
+  if actual == expected
+    then pure ()
+    else fail $ ident ++ ": expected " ++ expected ++ " but got " ++ actual
+