What the ZIP archiver does
Select any number of files and the tool packs them into a single .zip archive, compressed, ready to download. It solves the everyday problems of sending many files: email attachment limits, upload forms that take one file, chat apps that mangle folders, and recipients who want one download instead of twenty. The archive is built with JSZip in your browser — the files are never uploaded, so it is safe for documents you would not put on a file-sharing service.
How ZIP compression works
Each file is compressed independently with DEFLATE — the same algorithm behind gzip and PNG — which finds repeated byte sequences and replaces them with short references, then encodes the result with Huffman coding. The archive stores each compressed file with its name, size, timestamp and a CRC-32 checksum, plus a central directory at the end that lists everything, so a program can find a file without reading the whole archive.
| File type | Typical compression | Why |
|---|---|---|
| Text, CSV, code, logs, HTML | 60–90% smaller | Highly repetitive |
| Office documents (.docx, .xlsx, .pptx) | 0–10% | Already ZIP-compressed internally |
| 0–20% | Streams are usually already compressed | |
| JPG, PNG, WebP, HEIC | 0–3% | Already compressed image formats |
| MP3, MP4, MKV | 0–2% | Already compressed media |
| Uncompressed BMP, WAV, TIFF | 30–80% | Raw data compresses well |
The takeaway: zipping photos and videos is about bundling, not shrinking. Zipping text and raw data can cut size dramatically.
Common uses
- Bundling a set of photos, scans or documents for one email attachment or one upload.
- Submitting an assignment, an application or a print job as a single file.
- Handing a client a batch of deliverables with filenames intact.
- Compressing exported text data (CSV, JSON, logs) before sending or storing.
- Getting around chat and messaging apps that recompress images — a zipped photo arrives untouched.
Limits and things to know
- Folders: the picker selects files; directory structure is not preserved. Files are stored at the root of the archive with their original names.
- Size: the archive is built in memory, so total input of a few hundred megabytes is fine on a desktop; multi-gigabyte sets should use desktop software.
- Duplicate names: two files with the same name will conflict; rename before selecting.
- No password: the archive is not encrypted. For confidential content, use 7-Zip or your OS tools with AES encryption, or encrypt the files first.
- Timestamps are set to the time of zipping, not the original file dates.
ZIP vs other archive formats
| Format | Opens everywhere? | Compression | Notes |
|---|---|---|---|
| ZIP | Yes — built into Windows, macOS, Linux, iOS, Android | Good | The safe default for sharing |
| 7z | Needs 7-Zip or similar | Better | Best for large archives you control both ends of |
| RAR | Needs WinRAR or an extractor | Better | Proprietary |
| tar.gz | Native on macOS/Linux; Windows 11 yes | Similar to ZIP | Preserves Unix permissions |