ZIP Viewer

Open a .zip archive and see exactly what is inside without unpacking it to disk. The viewer reads the archive's central directory and lists every file and folder with its uncompressed size, compression method and ratio, and timestamp, and it can preview text files — source code, JSON, Markdown, CSV — by decompressing just that one entry on demand. It runs entirely in your browser, so the archive is never uploaded and you can safely inspect a download before trusting its contents.

Read locally in your browser — nothing is uploaded.

How to use the ZIP Viewer

Choose a .zip file, or click Example to build a small archive in your browser and inspect it. The viewer reads the archive's central directory — the index ZIP keeps at the end of the file — and lists every entry as an indented tree, so folders and the files within them sit where you expect. For each file you see its name, its uncompressed size, the compression method (Stored, Deflate, BZIP2, LZMA) with the space saved as a percentage, and the stored modification date. A summary line at the top reports the file and folder counts and the overall packed-versus-unpacked size.

Files that look like text — by extension such as .txt, .md, .json, .js, .csv, .xml, .svg and many more — get a preview button. Clicking it decompresses only that one entry (using a built-in Deflate decoder for the common case, or reading it directly when the entry is stored uncompressed) and shows the first portion of its contents inline; click again to hide it. Nothing else is decompressed, so even a large archive stays responsive. Encrypted entries are flagged with a lock and cannot be previewed, and the whole process happens locally: the archive's bytes are read from the file you picked and never sent anywhere, which is exactly what you want when checking the contents of a download before extracting it.

The ZIP format & why a viewer helps

ZIP is the most common archive format in the world. It bundles many files into one, compressing each independently, and it underlies far more than the .zip files you download: Java .jar and .war packages, Android .apks, EPUB e-books, and the modern Office formats .docx, .xlsx and .pptx are all ZIP archives with a particular set of files inside. Understanding what is in a ZIP therefore lets you understand a surprising range of files.

Structurally a ZIP file is laid out back-to-front from how you might expect. Each compressed file is stored with a small local header followed by its data, one after another. Then, at the very end of the file, comes the central directory: a compact index listing every entry with its name, sizes, CRC checksum, compression method, timestamp, and the offset of its local header. A final end-of-central-directory record points to where that index begins. Reading the central directory is how any ZIP tool learns the contents of an archive instantly, without scanning the whole file — and it is why a viewer can show you the full file list even for a large archive in an instant. Dates are stored in an old packed DOS format squeezed into two 16-bit words, which is why ZIP timestamps have two-second resolution and no time zone.

Most entries are compressed with Deflate, the same algorithm behind gzip and PNG, though an entry can also be stored (kept verbatim, common for already-compressed data like images) or use newer methods such as BZIP2 or LZMA. A browser viewer is handy because it answers the everyday questions — what is in this archive, how big are the files, is this the thing I expected to download — without extracting anything to disk, without a command-line tool, and without uploading a potentially sensitive bundle to an online service. Because it only reads the index and decompresses individual files on request, it is both fast and safe for inspecting archives from untrusted sources.

Common use cases

  • Check a download before extracting. See exactly what files an archive contains, and whether anything looks unexpected, before unpacking it to disk.
  • Peek inside an Office or EPUB file. Open a .docx, .xlsx or .epub as the ZIP it really is and read the XML or assets within.
  • Inspect a build artifact. List the contents of a .jar, .war or .apk to confirm what was packaged, and preview manifest or config files.
  • Audit an archive privately. Review a confidential bundle locally without uploading it to an online extractor.

Frequently asked questions

Is my archive uploaded anywhere?
No. The file is read entirely in your browser from a local File object. Only the central-directory index is parsed up front, and individual files are decompressed in-memory when you click preview. No bytes are sent to any server, which you can confirm in your browser's Network tab.

Can it extract or download the files?
It previews the contents of text files in place but does not write extracted files to disk. The goal is fast, safe inspection — seeing what an archive contains and reading individual text entries — rather than full extraction, which your operating system already does well.

Which compression methods are supported for preview?
Stored (uncompressed) and Deflate entries can be previewed, which covers the overwhelming majority of real-world ZIPs. Entries using BZIP2 or LZMA are listed with their size and method but are not decompressed for preview. Encrypted entries are flagged and cannot be read.

Does it work on .docx, .jar and .apk files?
Yes. Those are all ZIP archives, so the viewer lists their internal files and can preview the text ones — the XML inside a .docx, the manifest inside a .jar, and so on. Their structure is just a normal ZIP central directory.

Why are some timestamps slightly odd?
ZIP stores modification times in the legacy DOS date/time format, which has two-second resolution and no time zone information. The viewer decodes that format faithfully, so the times you see match what is recorded in the archive rather than your local clock.