Unzip files online without uploading them anywhere

Why "without uploading" matters

There are several distinct reasons to insist on no upload, and they are not all the same:

Confidentiality of contents is the obvious one. A zip of a client build, signed contracts, salary spreadsheets, or unreleased source code should not be sitting on a random server you cannot audit. The moment you upload, you are trusting that operator with the data, with their backups, with their logs, and with anyone who later compromises them.

Company and data-handling policies often forbid it outright. GDPR, HIPAA, SOC 2 commitments, and internal IP rules can all turn a quick "just paste it here" into a real incident. A tool that provably does not transmit the file sidesteps that whole category of risk and paperwork.

You also avoid unknown servers entirely — no need to vet a vendor, sign a DPA, or wonder which country the box is in. And because there is no server doing work, there is no account to create, no queue to wait in when the site is busy, and no per-file size tier tied to a subscription.

• Contents stay on your device — no server copy, no exfiltration.
• Compatible with strict data-handling and confidentiality policies.
• No third-party server to vet, trust, or worry about being breached later.
• No account, no sign-up, no upload queue or line limits.

How a no-upload unzip actually works

A traditional server-side unzipper receives your bytes over HTTP, runs a decompression library on the server, and streams results back. A client-side tool instead ships the decompression logic to you — as JavaScript (or, in some tools, WebAssembly) bundled in the page — and runs it inside your browser tab. The file is read from disk into the page's memory via the browser's file APIs, parsed locally, and rendered. Nothing about the archive is sent anywhere.

ZipTool uses the zip.js library for this. zip.js implements ZIP format parsing — central directory, local file headers, deflate/inflate — purely in JavaScript; it does not rely on WebAssembly. Your browser is the only machine that ever sees the decompressed data.

The practical consequence: after the page and its scripts have loaded, no further network access is required. You can open a zip from disk, browse it, and preview every entry with the Wi-Fi turned off. That is the honest test of a "no upload" claim, and you can run it yourself (see the verification note below).

Step-by-step: unzip a file without uploading it

Open the tool in a modern browser (Chrome, Firefox, Safari, or Edge all work). Then:

1. Drop or pick the archive. Drag the .zip onto the page, or use the file picker to select it from disk. There is no "Upload" button because nothing gets uploaded. The file tree appears almost instantly — only local disk and CPU are involved, so small-to-medium archives open in well under a second.

2. Browse the file tree. Folders expand inline; you can search across filenames to jump to an entry. State is kept per archive, so you can load more than one zip and switch between them without losing your place.

3. Preview any entry in place. Code files open in a syntax-highlighting editor (Monaco, the same engine behind VS Code); images, audio, video, and PDFs render directly; ZIP-based formats like .apk, .epub, .jar, .whl, .xpi, .war, Office .docx/.xlsx, and .kmz open just like plain .zip. A zip nested inside another zip can be added to the list and browsed separately.

4. Confirm nothing was written or sent. The archive is held only in that tab's memory. Close the tab and it is gone — nothing is saved to disk on your machine, and nothing was transmitted to any server.

You can also load a zip from a URL instead of disk via a deep link like ?zip=https://example.com/build.zip&file=src/index.js. Note the difference: that URL fetches the archive into the browser so it can be parsed client-side (the file is still parsed locally, not server-side), but fetching the archive itself does require network access at that moment.

Honest limitations

Client-side parsing trades server capacity for your browser's resources, so the bounds are different from a server tool:

Memory is the main ceiling. The browser tab must hold the archive (and the entries you open) in memory. Very large archives — typically approaching or past a few hundred MB to low GB depending on your machine and browser — can hit tab memory limits and become sluggish or fail to open. A 50 MB zip of source is effortless; a 4 GB archive is not what this tool is for.

Format support is ZIP and ZIP-based containers only. The formats above (.apk, .epub, .jar, .whl, .xpi, .war, OOXML, .kmz) are all ZIP under the hood, so they work. RAR (.rar) and 7z (.7z) are different archive formats with their own codecs and are not supported here.

Previews are read-only. You can view, search, and preview entries, but you cannot re-zip, edit entries in place, batch-extract the whole archive to disk, or convert formats. This is a viewer, not a compression utility.

One accuracy caveat worth stating plainly: client-side processing is a privacy guarantee (your data is not uploaded), not a blanket safety guarantee. A malicious archive is still malicious. A zip bomb like 42.zip — roughly 42 KB compressed, designed to expand into nested layers totalling petabytes — can still exhaust a tab's memory and crash it, because the browser dutifully parses what it is handed. Parsing also runs JavaScript in a sandboxed tab where browser or library bugs are theoretically exploitable, and any file you later extract and run elsewhere can still be malware. The improvement is that the contents are not exfiltrated, not that opening a file is risk-free. More on this distinction in the security and privacy page.

When to use a local tool instead

An in-browser viewer is not always the right answer. For completeness, the local alternatives and where each fits:

The unzip command line (Linux, macOS, and Windows via tar or WSL) is the fastest path for scripted or bulk extraction and has zero trust surface — it is already on your machine. Reach for it when you want to extract everything to disk or work in a terminal. The trade-off: no in-place preview, so you extract before you can see what is inside.

7-Zip (Windows, and p7zip on Linux/macOS) handles far more formats than ZIP — including .rar and .7z — and is a good fit when you have a non-ZIP archive, when the file is too large for a browser tab, or when you want to extract to disk. The trade-off: it is a local install, and a locked-down environment may restrict installing software.

OS built-ins (double-click "Extract All" on Windows, Archive Utility on macOS) are zero-install and fine for ordinary .zip extraction to disk. They are less useful when you want to preview a single file inside the archive without unpacking the whole thing — which is exactly the gap ZipTool fills.

Rule of thumb: preview-only, no install, confidentiality-first, and small-to-medium ZIP-based archives → the in-browser tool. Bulk extraction to disk, non-ZIP formats, or archives past a few hundred MB → a local extractor.

Verify it for yourself

You do not have to take "no upload" on faith — prove it in a few seconds:

Open your browser's DevTools (F12 or Cmd+Opt+I), switch to the Network tab, and load an archive. You will see the page's own static assets load, and then nothing — no request carrying your file leaves the tab. The cleaner test: load the tool, then turn off your network (disable Wi-Fi or pull the cable), and only then drop in a zip. It opens and previews exactly as before, because the work was never going to depend on the network.

If you want the deeper walkthrough of what client-side processing does and does not protect — including the privacy-vs-safety line and what data, if any, the site itself collects — read the security and privacy page, or jump straight to the private zip viewer overview.

Frequently asked questions