diff --git a/effectful/CHANGELOG.md b/effectful/CHANGELOG.md
index feefec40..33cb0038 100644
--- a/effectful/CHANGELOG.md
+++ b/effectful/CHANGELOG.md
@@ -1,4 +1,8 @@
 # effectful-2.7.0.0 (2026-??-??)
+* Add `OsPath` variants of the `FilePath` based APIs
+  (`Effectful.FileSystem.OsPath` for `System.Directory.OsPath` and
+  `Effectful.FileSystem.File.OsPath` for `System.File.OsPath` from the
+  `file-io` package).
 * `runInBoundThread` and `runInUnboundThread` from `Effectful.Concurrent` no
   longer run the computation in a cloned environment, so changes to thread-local
   effects made within are no longer discarded.
diff --git a/effectful/effectful.cabal b/effectful/effectful.cabal
index 4f2bef4c..9c5d79d0 100644
--- a/effectful/effectful.cabal
+++ b/effectful/effectful.cabal
@@ -59,8 +59,10 @@ library
     build-depends:    base                >= 4.18      && < 5
                     , async               >= 2.2.5
                     , bytestring          >= 0.10
-                    , directory           >= 1.3.2
+                    , directory           >= 1.3.8
                     , effectful-core      >= 2.7.0.0   && < 2.7.1.0
+                    , file-io             >= 0.1.4
+                    , filepath            >= 1.4.100
                     , process             >= 1.6.9
                     , strict-mutable-base >= 1.1.0.0
                     , time                >= 1.9.2
@@ -83,11 +85,13 @@ library
                      Effectful.Console.ByteString.Lazy
                      Effectful.Environment
                      Effectful.FileSystem
+                     Effectful.FileSystem.File.OsPath
                      Effectful.FileSystem.IO
                      Effectful.FileSystem.IO.ByteString
                      Effectful.FileSystem.IO.ByteString.Builder
                      Effectful.FileSystem.IO.ByteString.Lazy
                      Effectful.FileSystem.IO.File
+                     Effectful.FileSystem.OsPath
                      Effectful.Prim.IORef
                      Effectful.Prim.IORef.Strict
                      Effectful.Process
@@ -143,10 +147,12 @@ test-suite test
     ghc-options:    -threaded -rtsopts -with-rtsopts=-N4
 
     build-depends:    base
+                    , bytestring
                     , containers
                     , effectful
                     , effectful-core
                     , exceptions
+                    , filepath
                     , lifted-base
                     , primitive
                     , random
@@ -166,6 +172,7 @@ test-suite test
                     EnvTests
                     EnvironmentTests
                     ErrorTests
+                    FileSystemTests
                     InputTests
                     LabeledTests
                     NonDetTests
diff --git a/effectful/src/Effectful/FileSystem/File/OsPath.hs b/effectful/src/Effectful/FileSystem/File/OsPath.hs
new file mode 100644
index 00000000..5866970d
--- /dev/null
+++ b/effectful/src/Effectful/FileSystem/File/OsPath.hs
@@ -0,0 +1,150 @@
+-- | Lifted "System.File.OsPath".
+module Effectful.FileSystem.File.OsPath
+  ( -- * Effect
+    FileSystem
+
+    -- ** Handlers
+  , runFileSystem
+
+    -- * Files
+  , IOMode (..)
+  , Handle
+  , openBinaryFile
+  , withFile
+  , withBinaryFile
+  , withFile'
+  , withBinaryFile'
+  , readFile
+  , readFile'
+  , writeFile
+  , writeFile'
+  , appendFile
+  , appendFile'
+  , openFile
+  , openExistingFile
+  , openTempFile
+  , openBinaryTempFile
+  , openTempFileWithDefaultPermissions
+  , openBinaryTempFileWithDefaultPermissions
+  ) where
+
+import Data.ByteString (ByteString)
+import Data.ByteString.Lazy qualified as BSL
+import Prelude hiding (appendFile, readFile, writeFile)
+import System.File.OsPath qualified as F
+import System.IO (Handle, IOMode (..))
+import System.OsPath (OsPath, OsString)
+
+import Effectful
+import Effectful.Dispatch.Static
+import Effectful.FileSystem.Effect
+
+-- | Lifted 'F.openBinaryFile'.
+openBinaryFile :: FileSystem :> es => OsPath -> IOMode -> Eff es Handle
+openBinaryFile path = unsafeEff_ . F.openBinaryFile path
+
+-- | Lifted 'F.withFile'.
+withFile
+  :: FileSystem :> es
+  => OsPath
+  -> IOMode
+  -> (Handle -> Eff es a)
+  -> Eff es a
+withFile path mode inner = unsafeSeqUnliftIO $ \unlift -> do
+  F.withFile path mode $ unlift . inner
+
+-- | Lifted 'F.withBinaryFile'.
+withBinaryFile
+  :: FileSystem :> es
+  => OsPath
+  -> IOMode
+  -> (Handle -> Eff es a)
+  -> Eff es a
+withBinaryFile path mode inner = unsafeSeqUnliftIO $ \unlift -> do
+  F.withBinaryFile path mode $ unlift . inner
+
+-- | Lifted 'F.withFile''.
+withFile'
+  :: FileSystem :> es
+  => OsPath
+  -> IOMode
+  -> (Handle -> Eff es a)
+  -> Eff es a
+withFile' path mode inner = unsafeSeqUnliftIO $ \unlift -> do
+  F.withFile' path mode $ unlift . inner
+
+-- | Lifted 'F.withBinaryFile''.
+withBinaryFile'
+  :: FileSystem :> es
+  => OsPath
+  -> IOMode
+  -> (Handle -> Eff es a)
+  -> Eff es a
+withBinaryFile' path mode inner = unsafeSeqUnliftIO $ \unlift -> do
+  F.withBinaryFile' path mode $ unlift . inner
+
+-- | Lifted 'F.readFile'.
+readFile :: FileSystem :> es => OsPath -> Eff es BSL.ByteString
+readFile = unsafeEff_ . F.readFile
+
+-- | Lifted 'F.readFile''.
+readFile' :: FileSystem :> es => OsPath -> Eff es ByteString
+readFile' = unsafeEff_ . F.readFile'
+
+-- | Lifted 'F.writeFile'.
+writeFile :: FileSystem :> es => OsPath -> BSL.ByteString -> Eff es ()
+writeFile path = unsafeEff_ . F.writeFile path
+
+-- | Lifted 'F.writeFile''.
+writeFile' :: FileSystem :> es => OsPath -> ByteString -> Eff es ()
+writeFile' path = unsafeEff_ . F.writeFile' path
+
+-- | Lifted 'F.appendFile'.
+appendFile :: FileSystem :> es => OsPath -> BSL.ByteString -> Eff es ()
+appendFile path = unsafeEff_ . F.appendFile path
+
+-- | Lifted 'F.appendFile''.
+appendFile' :: FileSystem :> es => OsPath -> ByteString -> Eff es ()
+appendFile' path = unsafeEff_ . F.appendFile' path
+
+-- | Lifted 'F.openFile'.
+openFile :: FileSystem :> es => OsPath -> IOMode -> Eff es Handle
+openFile path = unsafeEff_ . F.openFile path
+
+-- | Lifted 'F.openExistingFile'.
+openExistingFile :: FileSystem :> es => OsPath -> IOMode -> Eff es Handle
+openExistingFile path = unsafeEff_ . F.openExistingFile path
+
+-- | Lifted 'F.openTempFile'.
+openTempFile
+  :: FileSystem :> es
+  => OsPath
+  -> OsString
+  -> Eff es (OsPath, Handle)
+openTempFile dir = unsafeEff_ . F.openTempFile dir
+
+-- | Lifted 'F.openBinaryTempFile'.
+openBinaryTempFile
+  :: FileSystem :> es
+  => OsPath
+  -> OsString
+  -> Eff es (OsPath, Handle)
+openBinaryTempFile dir = unsafeEff_ . F.openBinaryTempFile dir
+
+-- | Lifted 'F.openTempFileWithDefaultPermissions'.
+openTempFileWithDefaultPermissions
+  :: FileSystem :> es
+  => OsPath
+  -> OsString
+  -> Eff es (OsPath, Handle)
+openTempFileWithDefaultPermissions dir =
+  unsafeEff_ . F.openTempFileWithDefaultPermissions dir
+
+-- | Lifted 'F.openBinaryTempFileWithDefaultPermissions'.
+openBinaryTempFileWithDefaultPermissions
+  :: FileSystem :> es
+  => OsPath
+  -> OsString
+  -> Eff es (OsPath, Handle)
+openBinaryTempFileWithDefaultPermissions dir =
+  unsafeEff_ . F.openBinaryTempFileWithDefaultPermissions dir
diff --git a/effectful/src/Effectful/FileSystem/OsPath.hs b/effectful/src/Effectful/FileSystem/OsPath.hs
new file mode 100644
index 00000000..4cf5aeb0
--- /dev/null
+++ b/effectful/src/Effectful/FileSystem/OsPath.hs
@@ -0,0 +1,345 @@
+-- | Lifted "System.Directory.OsPath".
+module Effectful.FileSystem.OsPath
+  ( -- * Effect
+    FileSystem
+
+    -- ** Handlers
+  , runFileSystem
+
+    -- * Actions on directories
+  , createDirectory
+  , createDirectoryIfMissing
+  , removeDirectory
+  , removeDirectoryRecursive
+  , removePathForcibly
+  , renameDirectory
+  , listDirectory
+  , getDirectoryContents
+
+    -- ** Current working directory
+  , getCurrentDirectory
+  , setCurrentDirectory
+  , withCurrentDirectory
+
+    -- * Pre-defined directories
+  , getHomeDirectory
+  , getXdgDirectory
+  , getXdgDirectoryList
+  , getAppUserDataDirectory
+  , getUserDocumentsDirectory
+  , getTemporaryDirectory
+
+    -- * Actions on files
+  , removeFile
+  , renameFile
+  , renamePath
+  , copyFile
+  , copyFileWithMetadata
+  , getFileSize
+  , canonicalizePath
+  , makeAbsolute
+  , makeRelativeToCurrentDirectory
+
+    -- * Existence tests
+  , doesPathExist
+  , doesFileExist
+  , doesDirectoryExist
+  , findExecutable
+  , findExecutables
+  , findExecutablesInDirectories
+  , findFile
+  , findFiles
+  , findFileWith
+  , findFilesWith
+
+    -- * Symbolic links
+  , createFileLink
+  , createDirectoryLink
+  , removeDirectoryLink
+  , pathIsSymbolicLink
+  , getSymbolicLinkTarget
+
+    -- * Permissions
+  , getPermissions
+  , setPermissions
+  , copyPermissions
+
+    -- * Timestamps
+  , getAccessTime
+  , getModificationTime
+  , setAccessTime
+  , setModificationTime
+
+    -- * Re-exports
+
+    -- ** Pre-defined directories
+  , D.XdgDirectory(..)
+  , D.XdgDirectoryList(..)
+
+    -- ** Existence tests
+  , D.exeExtension
+
+    -- ** Permissions
+  , D.Permissions
+  , D.emptyPermissions
+  , D.readable
+  , D.writable
+  , D.executable
+  , D.searchable
+  , D.setOwnerReadable
+  , D.setOwnerWritable
+  , D.setOwnerExecutable
+  , D.setOwnerSearchable
+  ) where
+
+import Data.Time (UTCTime)
+import System.Directory.OsPath qualified as D
+import System.OsPath (OsPath, OsString)
+
+import Effectful
+import Effectful.Dispatch.Static
+import Effectful.FileSystem.Effect
+
+----------------------------------------
+-- Actions on directories
+
+-- | Lifted 'D.createDirectory'.
+createDirectory :: FileSystem :> es => OsPath -> Eff es ()
+createDirectory = unsafeEff_ . D.createDirectory
+
+-- | Lifted 'D.createDirectoryIfMissing'.
+createDirectoryIfMissing :: FileSystem :> es => Bool -> OsPath -> Eff es ()
+createDirectoryIfMissing doCreateParents =
+  unsafeEff_ . D.createDirectoryIfMissing doCreateParents
+
+-- | Lifted 'D.removeDirectory'.
+removeDirectory :: FileSystem :> es => OsPath -> Eff es ()
+removeDirectory = unsafeEff_ . D.removeDirectory
+
+-- | Lifted 'D.removeDirectoryRecursive'.
+removeDirectoryRecursive :: FileSystem :> es => OsPath -> Eff es ()
+removeDirectoryRecursive = unsafeEff_ . D.removeDirectoryRecursive
+
+-- | Lifted 'D.removePathForcibly'.
+removePathForcibly :: FileSystem :> es => OsPath -> Eff es ()
+removePathForcibly = unsafeEff_ . D.removePathForcibly
+
+-- | Lifted 'D.renameDirectory'.
+renameDirectory :: FileSystem :> es => OsPath -> OsPath -> Eff es ()
+renameDirectory old = unsafeEff_ . D.renameDirectory old
+
+-- | Lifted 'D.listDirectory'.
+listDirectory :: FileSystem :> es => OsPath -> Eff es [OsPath]
+listDirectory = unsafeEff_ . D.listDirectory
+
+-- | Lifted 'D.getDirectoryContents'.
+getDirectoryContents :: FileSystem :> es => OsPath -> Eff es [OsPath]
+getDirectoryContents = unsafeEff_ . D.getDirectoryContents
+
+----------------------------------------
+-- Current working directory
+
+-- | Lifted 'D.getCurrentDirectory'.
+getCurrentDirectory :: FileSystem :> es => Eff es OsPath
+getCurrentDirectory = unsafeEff_ D.getCurrentDirectory
+
+-- | Lifted 'D.setCurrentDirectory'.
+setCurrentDirectory :: FileSystem :> es => OsPath -> Eff es ()
+setCurrentDirectory = unsafeEff_ . D.setCurrentDirectory
+
+-- | Lifted 'D.withCurrentDirectory'.
+withCurrentDirectory :: FileSystem :> es => OsPath -> Eff es a -> Eff es a
+withCurrentDirectory path = unsafeLiftMapIO (D.withCurrentDirectory path)
+
+----------------------------------------
+-- Pre-defined directories
+
+-- | Lifted 'D.getHomeDirectory'.
+getHomeDirectory :: FileSystem :> es => Eff es OsPath
+getHomeDirectory = unsafeEff_ D.getHomeDirectory
+
+-- | Lifted 'D.getXdgDirectory'.
+getXdgDirectory
+  :: FileSystem :> es
+  => D.XdgDirectory
+  -> OsPath
+  -> Eff es OsPath
+getXdgDirectory xdgDir = unsafeEff_ . D.getXdgDirectory xdgDir
+
+-- | Lifted 'D.getXdgDirectoryList'.
+getXdgDirectoryList
+  :: FileSystem :> es
+  => D.XdgDirectoryList
+  -> Eff es [OsPath]
+getXdgDirectoryList = unsafeEff_ . D.getXdgDirectoryList
+
+-- | Lifted 'D.getAppUserDataDirectory'.
+getAppUserDataDirectory :: FileSystem :> es => OsPath -> Eff es OsPath
+getAppUserDataDirectory = unsafeEff_ . D.getAppUserDataDirectory
+
+-- | Lifted 'D.getUserDocumentsDirectory'.
+getUserDocumentsDirectory :: FileSystem :> es => Eff es OsPath
+getUserDocumentsDirectory = unsafeEff_ D.getUserDocumentsDirectory
+
+-- | Lifted 'D.getTemporaryDirectory'.
+getTemporaryDirectory :: FileSystem :> es => Eff es OsPath
+getTemporaryDirectory = unsafeEff_ D.getTemporaryDirectory
+
+----------------------------------------
+-- Actions on files
+
+-- | Lifted 'D.removeFile'.
+removeFile :: FileSystem :> es => OsPath -> Eff es ()
+removeFile = unsafeEff_ . D.removeFile
+
+-- | Lifted 'D.renameFile'.
+renameFile :: FileSystem :> es => OsPath -> OsPath -> Eff es ()
+renameFile old = unsafeEff_ . D.renameFile old
+
+-- | Lifted 'D.renamePath'.
+renamePath :: FileSystem :> es => OsPath -> OsPath -> Eff es ()
+renamePath old = unsafeEff_ . D.renamePath old
+
+-- | Lifted 'D.copyFile'.
+copyFile :: FileSystem :> es => OsPath -> OsPath -> Eff es ()
+copyFile src = unsafeEff_ . D.copyFile src
+
+-- | Lifted 'D.copyFileWithMetadata'.
+copyFileWithMetadata :: FileSystem :> es => OsPath -> OsPath -> Eff es ()
+copyFileWithMetadata src = unsafeEff_ . D.copyFileWithMetadata src
+
+-- | Lifted 'D.getFileSize'.
+getFileSize :: FileSystem :> es => OsPath -> Eff es Integer
+getFileSize = unsafeEff_ . D.getFileSize
+
+-- | Lifted 'D.canonicalizePath'.
+canonicalizePath :: FileSystem :> es => OsPath -> Eff es OsPath
+canonicalizePath = unsafeEff_ . D.canonicalizePath
+
+-- | Lifted 'D.makeAbsolute'.
+makeAbsolute :: FileSystem :> es => OsPath -> Eff es OsPath
+makeAbsolute = unsafeEff_ . D.makeAbsolute
+
+-- | Lifted 'D.makeRelativeToCurrentDirectory'.
+makeRelativeToCurrentDirectory
+  :: FileSystem :> es
+  => OsPath
+  -> Eff es OsPath
+makeRelativeToCurrentDirectory = unsafeEff_ . D.makeRelativeToCurrentDirectory
+
+----------------------------------------
+-- Existence tests
+
+-- | Lifted 'D.doesPathExist'.
+doesPathExist :: FileSystem :> es => OsPath -> Eff es Bool
+doesPathExist = unsafeEff_ . D.doesPathExist
+
+-- | Lifted 'D.doesFileExist'.
+doesFileExist :: FileSystem :> es => OsPath -> Eff es Bool
+doesFileExist = unsafeEff_ . D.doesFileExist
+
+-- | Lifted 'D.doesDirectoryExist'.
+doesDirectoryExist :: FileSystem :> es => OsPath -> Eff es Bool
+doesDirectoryExist = unsafeEff_ . D.doesDirectoryExist
+
+-- | Lifted 'D.findExecutable'.
+findExecutable :: FileSystem :> es => OsString -> Eff es (Maybe OsPath)
+findExecutable = unsafeEff_ . D.findExecutable
+
+-- | Lifted 'D.findExecutables'.
+findExecutables :: FileSystem :> es => OsString -> Eff es [OsPath]
+findExecutables = unsafeEff_ . D.findExecutables
+
+-- | Lifted 'D.findExecutablesInDirectories'.
+findExecutablesInDirectories
+  :: FileSystem :> es
+  => [OsPath]
+  -> OsString
+  -> Eff es [OsPath]
+findExecutablesInDirectories dirs =
+  unsafeEff_ . D.findExecutablesInDirectories dirs
+
+-- | Lifted 'D.findFile'.
+findFile :: FileSystem :> es => [OsPath] -> OsString -> Eff es (Maybe OsPath)
+findFile dirs = unsafeEff_ . D.findFile dirs
+
+-- | Lifted 'D.findFiles'.
+findFiles :: FileSystem :> es => [OsPath] -> OsString -> Eff es [OsPath]
+findFiles dirs = unsafeEff_ . D.findFiles dirs
+
+-- | Lifted 'D.findFileWith'.
+findFileWith
+  :: FileSystem :> es
+  => (OsPath -> Eff es Bool)
+  -> [OsPath]
+  -> OsString
+  -> Eff es (Maybe OsPath)
+findFileWith p dirs n = unsafeSeqUnliftIO $ \unlift -> do
+  D.findFileWith (unlift . p) dirs n
+
+-- | Lifted 'D.findFilesWith'.
+findFilesWith
+  :: FileSystem :> es
+  => (OsPath -> Eff es Bool)
+  -> [OsPath]
+  -> OsString
+  -> Eff es [OsPath]
+findFilesWith p dirs ns = unsafeSeqUnliftIO $ \unlift -> do
+  D.findFilesWith (unlift . p) dirs ns
+
+----------------------------------------
+-- Symbolic links
+
+-- | Lifted 'D.createFileLink'.
+createFileLink :: FileSystem :> es => OsPath -> OsPath -> Eff es ()
+createFileLink target = unsafeEff_ . D.createFileLink target
+
+-- | Lifted 'D.createDirectoryLink'.
+createDirectoryLink :: FileSystem :> es => OsPath -> OsPath -> Eff es ()
+createDirectoryLink target = unsafeEff_ . D.createDirectoryLink target
+
+-- | Lifted 'D.removeDirectoryLink'.
+removeDirectoryLink :: FileSystem :> es => OsPath -> Eff es ()
+removeDirectoryLink = unsafeEff_ . D.removeDirectoryLink
+
+-- | Lifted 'D.pathIsSymbolicLink'.
+pathIsSymbolicLink :: FileSystem :> es => OsPath -> Eff es Bool
+pathIsSymbolicLink = unsafeEff_ . D.pathIsSymbolicLink
+
+-- | Lifted 'D.getSymbolicLinkTarget'.
+getSymbolicLinkTarget :: FileSystem :> es => OsPath -> Eff es OsPath
+getSymbolicLinkTarget = unsafeEff_ . D.getSymbolicLinkTarget
+
+----------------------------------------
+-- Permissions
+
+-- | Lifted 'D.getPermissions'.
+getPermissions :: FileSystem :> es => OsPath -> Eff es D.Permissions
+getPermissions = unsafeEff_ . D.getPermissions
+
+-- | Lifted 'D.setPermissions'.
+setPermissions :: FileSystem :> es => OsPath -> D.Permissions -> Eff es ()
+setPermissions path = unsafeEff_ . D.setPermissions path
+
+-- | Lifted 'D.copyPermissions'.
+copyPermissions :: FileSystem :> es => OsPath -> OsPath -> Eff es ()
+copyPermissions src = unsafeEff_ . D.copyPermissions src
+
+----------------------------------------
+-- Timestamps
+
+-- | Lifted 'D.getAccessTime'.
+getAccessTime :: FileSystem :> es => OsPath -> Eff es UTCTime
+getAccessTime = unsafeEff_ . D.getAccessTime
+
+-- | Lifted 'D.getModificationTime'.
+getModificationTime :: FileSystem :> es => OsPath -> Eff es UTCTime
+getModificationTime = unsafeEff_ . D.getModificationTime
+
+-- | Lifted 'D.setAccessTime'.
+setAccessTime :: FileSystem :> es => OsPath -> UTCTime -> Eff es ()
+setAccessTime path = unsafeEff_ . D.setAccessTime path
+
+-- | Lifted 'D.setModificationTime'.
+setModificationTime :: FileSystem :> es => OsPath -> UTCTime -> Eff es ()
+setModificationTime path = unsafeEff_ . D.setModificationTime path
diff --git a/effectful/tests/FileSystemTests.hs b/effectful/tests/FileSystemTests.hs
new file mode 100644
index 00000000..14897a8f
--- /dev/null
+++ b/effectful/tests/FileSystemTests.hs
@@ -0,0 +1,53 @@
+module FileSystemTests (fileSystemTests) where
+
+import Data.ByteString.Char8 qualified as BS8
+import System.OsPath ((</>))
+import System.OsPath qualified as OsPath
+import Test.Tasty
+import Test.Tasty.HUnit
+
+import Effectful
+import Effectful.FileSystem.File.OsPath qualified as F
+import Effectful.FileSystem.OsPath
+import Effectful.Temporary
+import Utils qualified as U
+
+fileSystemTests :: TestTree
+fileSystemTests = testGroup "FileSystem"
+  [ testCase "OsPath directory operations" test_directoryOperations
+  , testCase "OsPath file operations" test_fileOperations
+  ]
+
+test_directoryOperations :: Assertion
+test_directoryOperations = runEff . runFileSystem . runTemporary $ do
+  withSystemTempDirectory "effectful" $ \tmpDirFp -> do
+    tmpDir <- OsPath.encodeUtf tmpDirFp
+    subDirName <- OsPath.encodeUtf "subdir"
+    let subDir = tmpDir </> subDirName
+    createDirectory subDir
+    subDirExists <- doesDirectoryExist subDir
+    U.assertBool "subdirectory was not created" subDirExists
+    newDirName <- OsPath.encodeUtf "newdir"
+    let newDir = tmpDir </> newDirName
+    renameDirectory subDir newDir
+    contents <- listDirectory tmpDir
+    U.assertEqual "unexpected directory contents" [newDirName] contents
+    removeDirectory newDir
+    newDirExists <- doesDirectoryExist newDir
+    U.assertBool "directory was not removed" (not newDirExists)
+
+test_fileOperations :: Assertion
+test_fileOperations = runEff . runFileSystem . runTemporary $ do
+  withSystemTempDirectory "effectful" $ \tmpDirFp -> do
+    tmpDir <- OsPath.encodeUtf tmpDirFp
+    fileName <- OsPath.encodeUtf "test.txt"
+    let file = tmpDir </> fileName
+    F.writeFile' file (BS8.pack "hello")
+    F.appendFile' file (BS8.pack " world")
+    contents <- F.readFile' file
+    U.assertEqual "unexpected file contents" (BS8.pack "hello world") contents
+    size <- getFileSize file
+    U.assertEqual "unexpected file size" 11 size
+    removeFile file
+    fileExists <- doesFileExist file
+    U.assertBool "file was not removed" (not fileExists)
diff --git a/effectful/tests/Main.hs b/effectful/tests/Main.hs
index f6ab13f3..9145e807 100644
--- a/effectful/tests/Main.hs
+++ b/effectful/tests/Main.hs
@@ -7,6 +7,7 @@ import ConcurrencyTests
 import EnvTests
 import EnvironmentTests
 import ErrorTests
+import FileSystemTests
 import InputTests
 import LabeledTests
 import NonDetTests
@@ -25,6 +26,7 @@ main = defaultMain $ testGroup "effectful"
   , envTests
   , environmentTests
   , errorTests
+  , fileSystemTests
   , inputTests
   , labeledTests
   , nonDetTests