A disk space analyser for Windows that tells you what is using the space, where it lives, what it is and how to free it — putting the main cause in the foreground and every other cause right behind it, heaviest first.
A free, open-source alternative to WinDirStat, TreeSize and WizTree — with one difference: it does not just show you a treemap, it names the cause and tells you what to do about it.
It is not yet another folder tree: every file is sorted into a cause (games, browser caches, project dependencies, restore points, hibernation…) with a plain-language explanation and a safety level — safe to delete, your call, leave alone.
- Windows 10/11, 64-bit. No dependencies: the portable executable already contains the .NET runtime.
- A drive with a million files is read in 5–15 seconds on an SSD.
- Interface in English and Italian (Settings → Language), MIT licensed.
From the Releases page:
Sonda-<version>-portable.zip— unzip and runSonda.exe; it installs nothing and writes nothing to the registry;Sonda-<version>-Setup.exe— installer (per-user, no administrator prompt).
The binaries are not code-signed — see below for why, and how to verify them yourself.
Sonda is not code-signed: a code signing certificate costs a few hundred euros a year, which an unpaid side project does not have. Windows SmartScreen therefore warns about an unknown publisher the first time you run it. The warning means "we have never seen this file before", not "this file is malicious".
You do not have to take my word for it. Every release is built by GitHub Actions from the public source in this repository, and the executable carries a build provenance attestation you can verify yourself:
gh attestation verify Sonda.exe --repo seremanuels-create/sondaThat command proves the binary was produced by this repository's workflow, from a specific
commit — something a hand-made copy cannot fake. SHA256SUMS.txt in the release lets you check
the download is intact. And if you would rather trust nothing at all: the whole thing builds
with .\build.ps1 in about a minute.
To run it past the warning: More info → Run anyway.
| Area | What is there |
|---|---|
| Main cause (top left) | The heaviest category: how much it takes, its share of the used space, what it is, how to free it, its safety level, and the heaviest folders inside it. |
| Other causes | Every other category, heaviest first, with a proportional bar. Click one for the detail. |
| Folders | A size-ordered explorer with breadcrumbs: on disk, share, file count, type, category, safety, date, notes (junction, access denied, cloud file). Below it, a treemap of the current folder. |
| Biggest files | The 2000 biggest files, filterable by text and category; each row says what it is, where it lives, which cause it belongs to and whether it is safe to delete. Multi-select → Recycle Bin. |
| Cause detail | Per cause: heaviest folders (double-click to enter) and biggest files. |
| File types | What the space-eating files actually are (video, audio, libraries, virtual disks, caches…), wherever they live. |
| Balance | The space Windows calls "used" against the space found in files: MFT (read from the volume or estimated), shadow copies (WMI), inaccessible folders, skipped junctions, and whatever is left "unattributed", with the reason why. |
Right-click any row: open in File Explorer, show in folder, enter, copy path, properties, delete (to the Recycle Bin, with a confirmation and a warning when the category is "leave alone").
The main column is on disk: the bytes the volume actually gives up.
- Sizes are rounded up to the cluster; on NTFS, files up to ~700 bytes count as 0 (they live inside the MFT record).
- NTFS-compressed and sparse files: real allocated size (
GetCompressedFileSize). - Cloud placeholders (OneDrive "online-only"): counted for their local footprint, which is usually zero.
RECALL_ON_OPENfiles are never opened, so nothing is downloaded behind your back. - Junctions and symbolic links are not followed: their content is counted where it really lives. Cloud/WCI/ProjFS reparse points are.
Windows\WinSxSis shown gross: many of its files are hard links shared withSystem32, so the real figure is lower. The app says so in the category description.
Safety labels are heuristics based on category and path: always look at the path before deleting. Everything goes through the Recycle Bin.
Sonda.exe C:\ open the UI and start analysing
Sonda.exe --report C:\ --out report.txt full text report, no window
Sonda.exe --report C:\ --csv folder plus three CSV files (biggest files, folders, causes)
Sonda.exe --report C:\ --lang en force the language for this run (it | en)
You need the .NET 9 SDK (winget install Microsoft.DotNet.SDK.9); for the installer also Inno Setup 6.
.\build.ps1 # portable single-file + zip + installer, into dist\
.\build.ps1 -SoloPortable # just the executableFor development, using the runtime already installed:
dotnet build -c Debug -p:SelfContained=false -p:PublishSingleFile=false
.\bin\Debug\net9.0-windows\win-x64\Sonda.exe C:\Authenticode signing is optional: .\build.ps1 -Firma uses the scripts named by the SONDA_FIRMA_PS1 (signs the binaries) and SONDA_FIRMA_CMD (called by Inno Setup for the setup and the uninstaller) environment variables.
Core\ Native.cs (Win32), Model.cs, Scanner.cs (parallel scan), Classifier.cs (categories, types, rules),
Analysis.cs (causes, top files, types, balance), ShadowStorage.cs (WMI), Report.cs (text/CSV),
ShellOps.cs (Explorer, Recycle Bin, elevation), Format.cs, Loc.cs + Strings.It.cs / Strings.En.cs
UI\ Theme.xaml, Converters.cs, Rows.cs (rows and column sorting), TreemapControl.cs (squarified treemap)
The scanner queues every folder and hands it to N threads using FileSystemEnumerable (one kernel call per block of entries, no stat per file), with extended \\?\ paths so the 260-character limit does not apply.
Everything lives in Core/Classifier.cs:
Categories— id, key, family (colour), safety level. Name, description and action come from the string tables;RootRules— paths anchored at the volume root, lowercase;*matches one segment,xxx*matches a prefix. The trailing number says how many segments below the anchor form the "group" shown in the cause detail;AnywhereRules— folder names that count anywhere (node_modules,.git,cache…), restricted to the contexts where they make sense;- file types:
Ext(key, extensions…)in the static constructor (each extension may be declared once only — a duplicate throws at startup).
Core/Strings.It.cs and Core/Strings.En.cs hold the same ~420 keys. To add a language: copy one of the files, translate the values, add the entry to the Lang enum and to the picker in SettingsWindow. Missing keys fall back to Italian, so a partial translation still runs.
Contributions are welcome, especially new rules for programs and games that eat a lot of space.
MIT — © 2026 StarVerb Audio.