diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,24 @@
+# Changelog
+All notable changes to the `align-equal` project will be documented in this file.
+
+## [0.1.1.0] - 2025-03-27
+- **Added**: Extracted core functions into a separate library module (`Data.Text.AlignEqual`).
+  - Refactored original `Main.hs` into executable and library components.
+  - Added `src/Data/Text/AlignEqual.hs` with core text alignment logic.
+  - Updated `app/Main.hs` to import and use `Data.Text.AlignEqual`.
+  - Adjusted `.cabal` file to include a new library section and dependencies.
+- **Added**: Haddock documentation for `Data.Text.AlignEqual`.
+  - Documented module purpose, `prefixLength`, `adjustLine`, and `adjustText` with descriptions, examples, and parameter annotations.
+- **Added**: Included `CHANGELOG.md` in the package documentation via `extra-doc-files` in `.cabal`.
+- **Maintained**: Compatibility with the existing executable.
+
+## [0.1.0.1] - 2025-03-10
+- **Fixed**: Relaxed `base` dependency constraint to `>=4.17 && <4.19`.
+- **Fixed**: Removed duplicate `extra-doc-files` entry in `.cabal` file.
+- **Added**: `README.md` with credit to Gabriella Gonzalez.
+- **Added**: Source repository link to `hub.darcs.net` in `.cabal` file.
+
+## [0.1.0.0] - 2025-03-10
+- **Initial Release**: Basic functionality for aligning text with equal signs.
+  - Implemented as a standalone executable in `Main.hs`.
+  - Initial project setup with `.cabal` and `LICENSE` files.
diff --git a/align-equal.cabal b/align-equal.cabal
--- a/align-equal.cabal
+++ b/align-equal.cabal
@@ -1,6 +1,6 @@
 cabal-version: 3.0
 name: align-equal
-version: 0.1.0.1
+version: 0.1.1.0
 license: MIT
 license-file: LICENSE
 author: Joonkyu Park (based on original work by Gabriella Gonzalez)
@@ -9,7 +9,10 @@
 description: A utility to adjust text lines by padding spaces before '=' based on the longest prefix.
 category: Text
 maintainer: vpark45@gmail.com
-extra-doc-files: README.md
+bug-reports: https://hub.darcs.net/vincent/align-equal/issues
+extra-doc-files:
+  CHANGELOG.md
+  README.md
 
 source-repository head
   type: darcs
@@ -22,9 +25,20 @@
   import: warnings
   main-is: Main.hs
   build-depends:
+    align-equal,
     base >=4.17 && <4.19,
-    safe >=0.3.21 && <0.4,
     text >=2.0.2 && <2.1,
 
   hs-source-dirs: app
+  default-language: Haskell2010
+
+library
+  import: warnings
+  exposed-modules: Data.Text.AlignEqual
+  build-depends:
+    base >=4.17 && <4.19,
+    safe >=0.3.21 && <0.4,
+    text >=2.0.2 && <2.1,
+
+  hs-source-dirs: src
   default-language: Haskell2010
diff --git a/app/Main.hs b/app/Main.hs
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -1,46 +1,7 @@
-{-# LANGUAGE OverloadedStrings #-}
-
 module Main where
 
-import           Data.Text    (Text)
-
-import qualified Data.Text    as T
-import qualified Data.Text.IO as TIO
-import           Safe
-
-prefixLength :: Text -> Int
-prefixLength line = T.length prefix
-  where
-    (prefix, _) = T.breakOn "=" line
-
-adjustLine :: Int -> Text -> Text
-adjustLine desiredPrefixLength oldLine = newLine
-  where
-    (prefix, suffix) = T.breakOn "=" oldLine
-
-    actualPrefixLength = T.length prefix
-
-    additionalSpaces = desiredPrefixLength - actualPrefixLength
-
-    spaces = T.replicate additionalSpaces " "
-
-    newLine = T.concat [ prefix, spaces, suffix ]
-
-adjustText :: Text -> Text
-adjustText oldText = newText
-  where
-    oldLines = T.lines oldText
-
-    prefixLengths = map prefixLength oldLines
-
-    newLines =
-      case maximumMay prefixLengths of
-        Nothing ->
-          []
-        Just desiredPrefixLength ->
-          map (adjustLine desiredPrefixLength) oldLines
-
-    newText = T.unlines newLines
+import           Data.Text.AlignEqual
+import qualified Data.Text.IO         as TIO
 
 main :: IO ()
 main = TIO.interact adjustText
diff --git a/src/Data/Text/AlignEqual.hs b/src/Data/Text/AlignEqual.hs
new file mode 100644
--- /dev/null
+++ b/src/Data/Text/AlignEqual.hs
@@ -0,0 +1,77 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+-- | A module providing functions for text alignment and padding.
+module Data.Text.AlignEqual where
+
+import           Data.Text (Text)
+import qualified Data.Text as T
+import           Safe
+
+-- | Calculates the number of characters preceding the first '=' sign in a text line.
+--
+-- >>> prefixLength "key=value"
+-- 3
+-- >>> prefixLength "a=b"
+-- 1
+-- >>> prefixLength "noequals"
+-- 8
+prefixLength
+  :: Text
+  -- ^ The input text line
+  -> Int
+  -- ^ The number of characters before the first '=' sign
+prefixLength line = T.length prefix
+  where
+    (prefix, _) = T.breakOn "=" line
+
+-- | Adjusts the prefix of a text line to a desired length by adding padding.
+--
+-- >>> adjustLine 5 "key=value"
+-- "key  =value"
+-- >>> adjustLine 3 "a=b"
+-- "a  =b"
+adjustLine
+  :: Int
+  -- ^ The desired prefix length
+  -> Text
+  -- ^ The text line to pad
+  -> Text
+  -- ^ The padded text line
+adjustLine desiredPrefixLength oldLine = newLine
+  where
+    (prefix, suffix) = T.breakOn "=" oldLine
+
+    actualPrefixLength = T.length prefix
+
+    additionalSpaces = desiredPrefixLength - actualPrefixLength
+
+    spaces = T.replicate additionalSpaces " "
+
+    newLine = T.concat [ prefix, spaces, suffix ]
+
+-- | Processes multi-line text to align all '=' signs across lines.
+--   Adjusts the prefix length of each line to match the maximum prefix length.
+--
+-- >>> adjustText "key=value\na=b"
+-- "key=value\na  =b"
+-- >>> adjustText "x=y\nlong=var"
+-- "x   =y\nlong=var"
+adjustText
+  :: Text
+  -- ^ The input text (possibly multi-line)
+  -> Text
+  -- ^ The aligned text
+adjustText oldText = newText
+  where
+    oldLines = T.lines oldText
+
+    prefixLengths = map prefixLength oldLines
+
+    newLines =
+      case maximumMay prefixLengths of
+        Nothing ->
+          []
+        Just desiredPrefixLength ->
+          map (adjustLine desiredPrefixLength) oldLines
+
+    newText = T.unlines newLines