diff --git a/.git-blame-ignore-revs b/.git-blame-ignore-revs
index f2b6102..0897ae2 100644
--- a/.git-blame-ignore-revs
+++ b/.git-blame-ignore-revs
@@ -1,2 +1,7 @@
+# top entries are newer, bottom ones older
+
+# Tools/dirDiff.fsx: fix formatting
+c4b5fa7631a87811fa1c916f9c12c758dd9348e6
+
 # Format F# files and scripts with fantomless v4.7.996
 14deca289798ce31908a77344324558c4bdc047b
diff --git a/Tools/dirDiff.fsx b/Tools/dirDiff.fsx
new file mode 100755
index 0000000..f81d0ce
--- /dev/null
+++ b/Tools/dirDiff.fsx
@@ -0,0 +1,314 @@
+#!/usr/bin/env dotnet fsi
+
+open System
+open System.IO
+open System.Diagnostics
+
+/// Validates that a path exists and is a directory
+let validatePath(path: string) : DirectoryInfo =
+    if not(Directory.Exists(path)) then
+        eprintfn "Error: Path '%s' does not exist." path
+        exit 1
+
+    let dirInfo = DirectoryInfo(path)
+
+    if not dirInfo.Exists then
+        eprintfn "Error: Path '%s' is not a valid directory." path
+        exit 1
+
+    dirInfo
+
+/// Check if a file is hidden (cross-platform: dot-prefix on Unix, Hidden attribute on Windows)
+let isHidden(file: FileInfo) =
+    file.Name.StartsWith(".")
+    || (file.Attributes &&& FileAttributes.Hidden) = FileAttributes.Hidden
+
+/// Gets all file details (name, size) and hidden file count for a directory
+let getFileDetails(dirInfo: DirectoryInfo) : Map<string, int64> * int =
+    let files = dirInfo.GetFiles("*", SearchOption.AllDirectories)
+    let fileMap = files |> Array.map(fun f -> f.Name, f.Length) |> Map.ofArray
+    let hiddenCount = files |> Array.filter isHidden |> Array.length
+    (fileMap, hiddenCount)
+
+/// Computes MD5 hash for a file using md5sum command
+let computeMd5sum(filePath: string) : string =
+    try
+        let psi = ProcessStartInfo()
+        psi.FileName <- "md5sum"
+        psi.Arguments <- sprintf "\"%s\"" filePath
+        psi.RedirectStandardOutput <- true
+        psi.RedirectStandardError <- true
+        psi.UseShellExecute <- false
+        psi.CreateNoWindow <- true
+
+        use proc = Process.Start(psi)
+        let output = proc.StandardOutput.ReadToEnd()
+        proc.WaitForExit()
+
+        if proc.ExitCode <> 0 then
+            let error = proc.StandardError.ReadToEnd()
+            failwithf "md5sum failed for '%s': %s" filePath error
+
+        // md5sum output format: "hash  filename"
+        output.Split(' ').[0].Trim()
+    with
+    | ex -> failwithf "Error computing MD5 for '%s': %s" filePath ex.Message
+
+/// Parse command line arguments
+let parseArgs(args: string []) =
+    let mutable folder1 = ""
+    let mutable folder2 = ""
+    let mutable isParallel = true // Default is parallel processing
+
+    let rec parse i =
+        if i >= args.Length then
+            ()
+        else
+            match args.[i] with
+            | "--non-parallel" ->
+                isParallel <- false
+                parse(i + 1)
+            | arg when arg.StartsWith("-") ->
+                eprintfn "Error: Unknown option '%s'" arg
+                exit 1
+            | arg when folder1 = "" ->
+                folder1 <- arg
+                parse(i + 1)
+            | arg when folder2 = "" ->
+                folder2 <- arg
+                parse(i + 1)
+            | _ ->
+                eprintfn "Error: Unexpected argument '%s'" args.[i]
+                exit 1
+
+    parse 0
+
+    if folder1 = "" || folder2 = "" then
+        None
+    else
+        Some(folder1, folder2, isParallel)
+
+/// Main comparison logic
+let compareFolders
+    (dir1: DirectoryInfo)
+    (dir2: DirectoryInfo)
+    (isParallel: bool)
+    =
+    printfn "Comparing folders:"
+    printfn "  Folder 1: %s" dir1.FullName
+    printfn "  Folder 2: %s" dir2.FullName
+    printfn ""
+
+    // Get file details
+    let (files1, hidden1) = getFileDetails dir1
+    let (files2, hidden2) = getFileDetails dir2
+
+    // Check 1: Compare number of files
+    let count1 = files1.Count
+    let count2 = files2.Count
+
+    if count1 <> count2 then
+        let visible1 = count1 - hidden1
+        let visible2 = count2 - hidden2
+        eprintfn "Error: Number of files differ."
+
+        eprintfn
+            "  Folder 1 has %d files (%d visible, %d hidden)"
+            count1
+            visible1
+            hidden1
+
+        eprintfn
+            "  Folder 2 has %d files (%d visible, %d hidden)"
+            count2
+            visible2
+            hidden2
+
+        exit 1
+
+    printfn "✓ Number of files matches: %d" count1
+
+    // in older versions of F#, Map.keys doesn't exist yet
+    let mapKeys(map: Map<'K, 'V>) =
+        seq {
+            for kvp in map do
+                yield kvp.Key
+        }
+
+    // Check 2: Compare file names
+    let names1 = Set.ofList(mapKeys files1 |> Seq.toList)
+    let names2 = Set.ofList(mapKeys files2 |> Seq.toList)
+
+    let onlyIn1 = Set.difference names1 names2
+    let onlyIn2 = Set.difference names2 names1
+
+    if not(Set.isEmpty onlyIn1) then
+        eprintfn "Error: Files only in folder 1: %A" onlyIn1
+        exit 1
+
+    if not(Set.isEmpty onlyIn2) then
+        eprintfn "Error: Files only in folder 2: %A" onlyIn2
+        exit 1
+
+    printfn "✓ File names match"
+
+    // Check 3: Compare file sizes
+    let sizeDifferences =
+        files1
+        |> Map.filter(fun name size1 ->
+            let size2 = Map.find name files2
+            size1 <> size2
+        )
+
+    if not(Map.isEmpty sizeDifferences) then
+        eprintfn "Error: File sizes differ for the following files:"
+
+        sizeDifferences
+        |> Map.iter(fun name size1 ->
+            let size2 = Map.find name files2
+
+            eprintfn
+                "  %s: %d bytes (folder 1) vs %d bytes (folder 2)"
+                name
+                size1
+                size2
+        )
+
+        exit 1
+
+    printfn "✓ File sizes match"
+
+    // Check 4: Compare MD5 checksums
+    // Prepare file pairs for comparison
+    let filePairs =
+        files1
+        |> Map.toArray
+        |> Array.map(fun (name, _) ->
+            let file1Path = Path.Combine(dir1.FullName, name)
+            let file2Path = Path.Combine(dir2.FullName, name)
+            (name, file1Path, file2Path)
+        )
+
+    let totalFiles = files1.Count
+    let mutable completedFiles = 0
+
+    // Progress update function
+    let updateProgress() =
+        completedFiles <- completedFiles + 1
+        let pct = int(float completedFiles / float totalFiles * 100.0)
+        let barWidth = 30
+
+        let filled =
+            int(float completedFiles / float totalFiles * float barWidth)
+
+        let bar =
+            String.replicate filled "="
+            + String.replicate (barWidth - filled) "-"
+
+        printf
+            "\r  Progress: [%s] %d/%d (%d%%)"
+            bar
+            completedFiles
+            totalFiles
+            pct
+
+        if completedFiles = totalFiles then
+            printfn ""
+
+    let filesWithDiffs =
+        if isParallel then
+            printfn "Computing MD5 checksums in parallel..."
+
+            // Process in batches of 20 using Async.Parallel
+            let batchSize = 20
+            let results = ResizeArray<_>()
+
+            filePairs
+            |> Array.chunkBySize batchSize
+            |> Array.iter(fun batch ->
+                let asyncWorkItems =
+                    batch
+                    |> Array.map(fun (name, path1, path2) ->
+                        async {
+                            let hash1 = computeMd5sum path1
+                            let hash2 = computeMd5sum path2
+                            return (name, hash1, hash2)
+                        }
+                    )
+
+                let batchResults =
+                    asyncWorkItems |> Async.Parallel |> Async.RunSynchronously
+
+                batchResults
+                |> Array.iter(fun r ->
+                    updateProgress()
+                    results.Add(r)
+                )
+            )
+
+            results.ToArray()
+            |> Array.filter(fun (_, hash1, hash2) -> hash1 <> hash2)
+        else
+            printfn "Computing MD5 checksums (sequential)..."
+
+            filePairs
+            |> Array.map(fun (name, path1, path2) ->
+                let hash1 = computeMd5sum path1
+                let hash2 = computeMd5sum path2
+                updateProgress()
+                (name, hash1, hash2)
+            )
+            |> Array.filter(fun (_, hash1, hash2) -> hash1 <> hash2)
+
+    if not(Array.isEmpty filesWithDiffs) then
+        eprintfn "Error: MD5 checksums differ for the following files:"
+
+        filesWithDiffs
+        |> Array.iter(fun (name, hash1, hash2) ->
+            eprintfn "  %s:" name
+            eprintfn "    Folder 1: %s" hash1
+            eprintfn "    Folder 2: %s" hash2
+        )
+
+        exit 1
+
+    printfn "✓ MD5 checksums match for all files"
+    printfn ""
+    printfn "SUCCESS: All files are identical!"
+
+/// Entry point
+let main(args: string []) : int =
+    match parseArgs args with
+    | None ->
+        eprintfn "Usage: dir-diff.fsx <folder1> <folder2> [--non-parallel]"
+        eprintfn ""
+
+        eprintfn
+            "Compares two folders and checks if their contents are identical."
+
+        eprintfn ""
+        eprintfn "Arguments:"
+        eprintfn "  folder1         Path to the first folder"
+        eprintfn "  folder2         Path to the second folder"
+
+        eprintfn
+            "  --non-parallel  Disable parallel processing (default: parallel)"
+
+        1 // error exit code
+
+    | Some(folder1Path, folder2Path, isParallel) ->
+        printfn "Validating paths..."
+        let dir1 = validatePath folder1Path
+        let dir2 = validatePath folder2Path
+
+        compareFolders dir1 dir2 isParallel
+
+        0 // Success exit code
+
+let exitCode =
+#if INTERACTIVE
+    main fsi.CommandLineArgs.[1..]
+#else
+    main(fsi.CommandLineArgs |> Array.tail)
+#endif
+exit exitCode