How to Preview What Is Inside a ZIP File Without Extracting It
Before you unpack a ZIP you did not make, it helps to know what is in it: how many files, how big, and whether anything looks wrong. Archive Viewer shows that without saving a single file.
See file names, folders and sizes without saving anything to your device.
See inside a ZIP in two steps
- Open Archive Viewer and add the ZIP with Select ZIP File.
- Read the summary and the list. The status line reads "Previewing 12 file(s) and 3 folder(s)."
Nothing is downloaded. The tool reads the archive's index, shows what it finds and stops there. When you decide you want files, you take them out with ZIP Extractor.
The summary block, line by line
| Line | What it counts |
|---|---|
| Total files | Entries that are files, not folders |
| Total folders | Folder entries stored in the archive |
| Uncompressed size | What the files will take once extracted |
| Compressed size | What they take inside the ZIP |
| Overall compression | Shown as a percentage "smaller" |
Each file also shows its own line in the form "2.4 MB to 900 KB (62% smaller)", with folders listed first and the rest in alphabetical order. The percentages are calculated from the sizes stored in the archive, so they describe the file as it was packed, not an estimate.
Reading the numbers: what they tell you
- Large uncompressed size, tiny ZIP. Text, logs and spreadsheets shrink a lot. If a 5 MB ZIP will expand to several gigabytes, check you have the room before extracting.
- Close to 0% smaller. Typical for JPG photos, MP4 video, PDFs that are already compressed, and ZIPs that were stored without compression. This is normal, not a fault.
- Folder count higher than expected. Archives made on some systems carry hidden folders, which can explain why the count seems off.
- File names with unfamiliar extensions. Anything executable, such as
.exe,.bator.js, inside a ZIP that is supposed to hold documents deserves a second look before you open it. The viewer does not scan files, it only lists them.
Which of the three ZIP tools do you need?
| Goal | Tool |
|---|---|
| Check names and sizes before saving anything | Archive Viewer |
| Save one or all files from an archive | ZIP Extractor |
| Make an archive from your own files | ZIP Creator |
A neat trick is to run your own freshly made archive through the viewer. A ZIP made by ZIP Creator will show close to 0% compression, because that tool stores files without compressing them. If you want to know why, the details are in how to create a ZIP file online.
Why previewing is quick
A ZIP keeps an index called the central directory with each entry's name, size and compressed size. The viewer reads that index and does not unpack any content, so even a large archive tends to appear almost at once. Extracting is slower because every file must actually be decompressed. This also explains a limit: the viewer shows what the index claims. It cannot show you what a document says inside, only that it is there.
A worked example makes the numbers concrete. Suppose a ZIP shows 14 files and 2 folders, an uncompressed size of 48 MB, a compressed size of 41 MB and "15% smaller". That is a typical mix of photos and PDFs. If the same archive instead said 48 MB uncompressed and 2 MB compressed, you would be looking at mostly text or spreadsheets, which is also fine, but worth knowing if disk space is tight.
Common situations
- A ZIP of scans from a client. Check the count and the file types first, then unpack. Scanned pages can be joined afterwards with this scan-to-PDF guide.
- A download that looks too small. If the archive should hold 200 photos and the viewer shows 3 files, the download probably stopped halfway. Fetch it again.
- A ZIP full of images. The names show the formats. If they are WebP or HEIC and your software complains, read how to tell what format an image really is.
A short checklist before you extract an unknown ZIP
- Does the file count match what the sender described? Three files when you were promised thirty usually means a broken download.
- Do the extensions fit the story? A contract should hold PDFs or Word files, photos should be JPG, PNG, WebP or HEIC.
- Is the uncompressed size something your device can hold? Add a margin for the extracted copies.
- Are there nested ZIPs inside? Archives within archives are legitimate sometimes, but they also hide content, so open them one level at a time.
- Do the names look like the sender's usual naming? Strange long names with double extensions such as
invoice.pdf.exeare a classic warning sign.
None of these is proof of anything, but together they catch most careless mistakes and many dubious files before they reach your device.
What the viewer cannot do
It does not open password-protected archives, and the tool says so with its message: "Could not read this ZIP file. It may be corrupted, encrypted, or not a valid ZIP archive." It reads ZIP only, so RAR and 7z files are out. It does not show the contents of the files, give you thumbnails, or scan for viruses. The archive is read in your browser and the tool states that it is not uploaded, though the JSZip library loads from a CDN when the page opens.
Frequently Asked Questions
Does Archive Viewer extract or download files?
No. It only reads the archive index and shows names, folders and sizes. To save files, use ZIP Extractor.
What does the compression percentage mean?
It compares each file packed size with its uncompressed size. Near 0% is normal for JPG, MP4 and other already compressed files.
Can I preview a password-protected ZIP?
No. Encrypted archives are not supported, and the tool shows a message that the file could not be read.
Why does it open so quickly?
It reads only the index at the end of the ZIP, not the file contents, so large archives usually show up almost instantly.
Does it check for viruses?
No. It lists what is inside. Be careful with unexpected executable files and scan anything you extract.
Does it work with RAR or 7z files?
No, ZIP archives only.