diff --git a/scls-util/src/Cardano/SCLS/Util/Tool.hs b/scls-util/src/Cardano/SCLS/Util/Tool.hs
index c0a4d1a..73783bc 100644
--- a/scls-util/src/Cardano/SCLS/Util/Tool.hs
+++ b/scls-util/src/Cardano/SCLS/Util/Tool.hs
@@ -1,6 +1,7 @@
 {-# LANGUAGE BlockArguments #-}
 {-# LANGUAGE RecordWildCards #-}
 
+-- | File manipulation utilities for SCLS files.
 module Cardano.SCLS.Util.Tool (splitFile, mergeFiles, extract, ExtractOptions (..)) where
 
 import Cardano.SCLS.Internal.Reader
@@ -13,7 +14,7 @@ import Cardano.Types.Namespace (Namespace (..))
 import Cardano.Types.Namespace qualified as Namespace
 import Cardano.Types.Network (NetworkId (Mainnet))
 import Cardano.Types.SlotNo (SlotNo (SlotNo))
-import Control.Exception (SomeException, catch)
+import Control.Exception (SomeException, bracket, catch)
 import Control.Monad (foldM)
 import Data.Function ((&))
 import Data.Map.Strict qualified as Map
@@ -24,6 +25,10 @@ import System.Directory (createDirectoryIfMissing)
 import System.FilePath ((</>))
 import System.IO
 
+{- | Split a single SCLS file into multiple files by namespace.
+Takes a source SCLS file and an output directory, and creates separate files
+for each namespace found in the source file.
+-}
 splitFile :: FilePath -> FilePath -> IO Result
 splitFile sourceFile outputDir = do
   putStrLn $ "Splitting file: " ++ sourceFile
@@ -54,6 +59,11 @@ splitFile sourceFile outputDir = do
       putStrLn $ "Error: " ++ show e
       pure OtherError
 
+{- | Merge multiple SCLS files into a single output file.
+
+Takes a list of input files and combines their namespace data into a single
+output file.
+-}
 mergeFiles :: FilePath -> [FilePath] -> IO Result
 mergeFiles _ [] = do
   putStrLn "No source files provided for merging"
@@ -66,25 +76,21 @@ mergeFiles outputFile sourceFiles = do
 
       putStrLn $ "Found " ++ show (Map.size nsToFiles) ++ " unique namespace(s)"
 
-      let stream =
-            S.each (Map.toList nsToFiles)
-              & S.mapM_ \(ns, files) -> do
-                S.each files
-                  & S.mapM
-                    ( \file -> do
-                        s <- withNamespacedData @RawBytes file ns $ \s ->
-                          -- eagerly load each stream to avoid issues with file handles
-                          -- FIXME: use a different data structure like Vector
-                          -- FIXME: concerns about loading entire namespace data into memory
-                          S.toList_ s
-                        pure (ns S.:> S.each s)
-                    )
-
-      serialize
-        outputFile
-        Mainnet
-        (SlotNo 1)
-        (defaultSerializationPlan & addChunks stream)
+      withNamespaceHandles nsToFiles $ \nsHandles -> do
+        let stream =
+              S.each nsHandles
+                & S.mapM_ \(ns, handles) -> do
+                  S.each handles
+                    & S.map
+                      ( \handle ->
+                          (ns S.:> namespacedData @RawBytes handle ns)
+                      )
+
+        serialize
+          outputFile
+          Mainnet
+          (SlotNo 1)
+          (defaultSerializationPlan & addChunks stream)
 
       putStrLn "Merge complete"
       pure Ok
@@ -106,11 +112,29 @@ mergeFiles outputFile sourceFiles = do
       )
       mempty
       files
+  -- Open file handles for each namespace's files, execute the given action,
+  -- and ensure all handles are closed afterwards.
+  withNamespaceHandles :: Map.Map Namespace [FilePath] -> ([(Namespace, [Handle])] -> IO a) -> IO a
+  withNamespaceHandles nsToFiles =
+    bracket
+      ( Map.foldrWithKey
+          ( \ns files acc -> do
+              handles <- mapM (\file -> openFile file ReadMode) files
+              (:) (ns, handles) <$> acc
+          )
+          (pure [])
+          nsToFiles
+      )
+      (mapM_ (mapM_ hClose . snd))
 
 data ExtractOptions = ExtractOptions
   { extractNamespaces :: Maybe [Namespace]
   }
 
+{- | Extract specific data from an SCLS file into a new file.
+Takes a source SCLS file, an output file, and extraction options specifying
+which data to extract.
+-}
 extract :: FilePath -> FilePath -> ExtractOptions -> IO Result
 extract sourceFile outputFile ExtractOptions{..} = do
   putStrLn $ "Extracting from file: " ++ sourceFile
@@ -119,26 +143,20 @@ extract sourceFile outputFile ExtractOptions{..} = do
     do
       Hdr{..} <- withHeader sourceFile pure
 
-      let chunks =
-            case extractNamespaces of
-              Nothing -> S.each []
-              Just nsList ->
-                S.each nsList
-                  & S.mapM
-                    ( \ns -> do
-                        s <- withNamespacedData @RawBytes sourceFile ns $ \s ->
-                          -- eagerly load each stream to avoid issues with file handles
-                          -- FIXME: use a different data structure like Vector
-                          -- FIXME: concerns about loading entire namespace data into memory
-                          S.toList_ s
-                        pure (ns S.:> S.each s)
-                    )
-
-      serialize
-        outputFile
-        networkId
-        slotNo
-        (defaultSerializationPlan & addChunks chunks)
+      withBinaryFile sourceFile ReadMode \handle -> do
+        let chunks =
+              case extractNamespaces of
+                Nothing -> S.each []
+                Just nsList ->
+                  S.each nsList
+                    & S.map
+                      (\ns -> (ns S.:> namespacedData @RawBytes handle ns))
+
+        serialize
+          outputFile
+          networkId
+          slotNo
+          (defaultSerializationPlan & addChunks chunks)
 
       pure Ok
     \(e :: SomeException) -> do