diff --git a/double-x-encoding.cabal b/double-x-encoding.cabal
--- a/double-x-encoding.cabal
+++ b/double-x-encoding.cabal
@@ -5,7 +5,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           double-x-encoding
-version:        1.1.0.0
+version:        1.1.1
 synopsis:       Encoding scheme to encode any Unicode string with only [0-9a-zA-Z_]
 description:    Double-X-Encoding is an encoding scheme to encode any Unicode string
                 with only characters from [0-9a-zA-Z_].
diff --git a/source/DoubleXEncoding.hs b/source/DoubleXEncoding.hs
--- a/source/DoubleXEncoding.hs
+++ b/source/DoubleXEncoding.hs
@@ -1,6 +1,19 @@
--- | Implementation of double-X-encoder and -decoder in Haskell
+{- | Implementation of Double-X-Encoding encoder and decoder in Haskell
+
+Main functions:
+
+* `doubleXEncode`
+* `doubleXEncodeGql`
+* `doubleXDecode`
+-}
+
 {- ORMOLU_DISABLE -}
 
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE MultiWayIf #-}
+
+
 module DoubleXEncoding where
 
 import Data.Function ((&))
@@ -13,7 +26,7 @@
 import Control.Monad (join)
 
 
--- | charEncode mapping in Haskell
+-- | Encoder mapping for ASCII characters.
 charEncode :: Char -> Char
 charEncode = \case
   ' ' -> '0'
@@ -61,6 +74,7 @@
   _ -> '\0'
 
 
+-- | Decoder mapping for ASCII characters.
 charDecode :: Char -> Char
 charDecode = \case
   '0' -> ' '
@@ -106,6 +120,8 @@
   _ -> '\0'
 
 
+-- | Map hex characters to an alternative hex alphabet
+-- ranging from a to p instead of 0 to f.
 hexShiftEncode :: Char -> Char
 hexShiftEncode = \case
   '0' -> 'a'
@@ -128,6 +144,7 @@
   _ -> '\0'
 
 
+-- | Map alternative hex alphabet back to the original hex alphabet.
 hexShiftDecode :: Char -> Char
 hexShiftDecode = \case
   'a' -> '0'
@@ -150,12 +167,24 @@
   _ -> '\0'
 
 
+{-|
+  Options for encoding:
+
+  [`encodeLeadingDigit`]: Encode the leading digit of the input string
+
+  [`encodeDoubleUnderscore`]: Encode double underscores `__` as `XXRXXR`
+
+  Especially relevant for GraphQL, as
+  [the spec](https://spec.graphql.org/October2021/#sec-Names)
+  does not allow leading digits or double underscores for field names.
+-}
 data EncodeOptions = EncodeOptions
   { encodeLeadingDigit :: Bool
   , encodeDoubleUnderscore :: Bool
   }
 
 
+-- | Encode a text using the Double-X-Encoding algorithm with provided options.
 doubleXEncodeWithOptions :: EncodeOptions -> Text -> Text
 doubleXEncodeWithOptions encodeOptions text =
   let
@@ -213,8 +242,8 @@
       encodeStandard text
 
 
-
-
+-- | Default options with no leading digit encoding
+-- and no double underscore encoding.
 defaultOptions :: EncodeOptions
 defaultOptions = EncodeOptions
     { encodeLeadingDigit = False
@@ -222,11 +251,17 @@
     }
 
 
+-- | Encode a text using the Double-X-Encoding algorithm.
+--
+-- >>> doubleXEncode "id-with.special$chars!"
+-- "idXXDwithXXEspecialXX4charsXX1"
 doubleXEncode :: Text -> Text
 doubleXEncode =
     doubleXEncodeWithOptions defaultOptions
 
 
+-- | Default options for GraphQL encoding.
+-- Leading digits or double underscores are not allowed for field names.
 gqlOptions :: EncodeOptions
 gqlOptions = EncodeOptions
     { encodeLeadingDigit = True
@@ -234,21 +269,28 @@
     }
 
 
+-- | Encode a text using the Double-X-Encoding algorithm with GraphQL options.
+--
+-- >>> doubleXEncodeGql "1FileFormat__"
+-- "XXZ1FileFormatXXRXXR"
 doubleXEncodeGql :: Text -> Text
 doubleXEncodeGql =
     doubleXEncodeWithOptions gqlOptions
 
 
-parseHex :: Text -> Int
-parseHex text =
-  case readHex (T.unpack text) of
-    [(int, "")] -> int
-    _ -> 0
-
-
+-- | Decode a Double-X-Encoding encoded text.
+--
+-- >>> doubleXDecode "idXXDwithXXEspecialXX4charsXX1"
+-- "id-with.special$chars!"
 doubleXDecode :: Text -> Text
 doubleXDecode text =
   let
+    parseHex :: Text -> Int
+    parseHex text =
+      case readHex (T.unpack text) of
+        [(int, "")] -> int
+        _ -> 0
+
     decodeWord :: Text -> (Text, Text)
     decodeWord word =
       let