Files & Networking
ZIP & RAR File Analyzer
Drop a .zip file to instantly list every file inside it — name, original size, compressed size and space saved — all in your browser without uploading a single byte. Also detects .rar and .7z formats with guidance on opening them.
What is a ZIP file?
A ZIP archive is a container that wraps one or more files into a single package, optionally compressing them to save space. The format was created in 1989 by Phil Katz and is now built into Windows, macOS and Linux — no third-party software required to open a basic ZIP. It is the most widely supported archive format on the web.
ZIP uses a central directory structure: a table at the end of the file lists every entry's name, size and location, which is how this analyzer can show you the full contents without unpacking anything.
ZIP vs. RAR — which should you use?
Both are archive formats, but they differ in important ways:
- ZIP — open standard, built into every modern OS, universally openable. Slightly lower compression ratio than RAR in some cases. Best for sharing files where the recipient may not have special software.
- RAR — proprietary format from WinRAR. Often compresses better than ZIP, especially for large collections of similar files. Requires third-party software to create (WinRAR, 7-Zip) but can be extracted by most archive tools. Also supports recovery records for repairing damaged archives.
- 7-Zip (.7z) — open format with excellent compression, often beating both ZIP and RAR. Free and open source. Less universally supported than ZIP out of the box.
For everyday use and sharing, ZIP wins on compatibility. For backup and storage where space matters, 7z or RAR can be worth it.
How ZIP compression works
The standard ZIP compression algorithm is Deflate, a combination of LZ77 (finds repeated byte sequences and replaces them with shorter references) and Huffman coding (assigns shorter bit sequences to more common patterns). Together they typically reduce text files by 60–80% and source code by 70–90%. Already-compressed files like JPEGs, MP4s or existing ZIPs see little or no reduction.
Compression ratio = (1 − compressed size ÷ original size) × 100%
A 75% ratio means the ZIP is 25% of the original size — four times smaller. This analyzer shows per-file and overall ratios so you can spot which files compress well and which don't.
How to use this ZIP file analyzer
- Drop or select a file. Drag a .zip file onto the drop zone, or click 'Choose file' to browse. Your file stays on your device — nothing is uploaded.
- Read the summary. File count, original size, compressed size and overall savings appear at the top.
- Browse the file list. Each row shows the filename, original size, compressed size, space saved (%) and compression method.
- For RAR or 7z. The tool identifies the format and tells you which free software to use to open it.
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Frequently asked questions
Is my file uploaded anywhere?
No. Everything runs entirely in your browser using the File API. Your file never leaves your device — nothing is sent to any server.
Can this tool open or convert RAR files?
It detects RAR archives and tells you the format, but cannot list or extract the contents — RAR is a proprietary format with no open client-side parser. Use 7-Zip (free, open source) or WinRAR to inspect or convert them.
What does the compression ratio mean?
It shows how much smaller the compressed file is compared to the originals. For example, 65% savings means the archive is 35% of the original total size — a 65% reduction. Higher is better for storage and transfer.
What compression methods does ZIP support?
The two most common are Store (0% compression, used for already-compressed files) and Deflate (the standard algorithm). Newer ZIP tools also use BZip2, LZMA and Zstandard for better ratios on some file types.
Can this tool extract files from a ZIP?
No — it lists the contents only, without extracting. This keeps the tool instant and private (no upload, no server). To actually unpack files, right-click the ZIP in Windows Explorer and choose 'Extract All', or use 7-Zip.
What is a ZIP file, and how is it different from RAR?
ZIP is an open, universally supported archive format built into Windows, macOS and Linux. RAR is a proprietary format created by WinRAR with slightly better compression in some cases, but requires third-party software to create (though many tools can extract it). For sharing files online, ZIP is generally the better choice for maximum compatibility.
Why are some files listed with 0% savings?
Files already compressed — JPEG images, MP4 videos, MP3 audio, existing ZIPs — don't compress further with Deflate. They're stored as-is inside the archive (method: Store), so compressed size ≈ original size and savings are near zero.