Gzip Header and Footer Inspector
Drop in a .gz file to read what its gzip wrapper records without unzipping the data inside: the original filename, the modification date, the source operating system, the compressed and uncompressed sizes, and the compression ratio. The file is parsed entirely in your browser and never uploaded.
How to inspect a gzip file
- Drag a .gz file onto the box, or click browse to pick one.
- Read the header report: original filename, sizes, ratio, OS and date.
- Check the flags and footer values to confirm the file is intact gzip.
Examples
A gzipped log file
access.log.gz (a 40 KB gzip from a Linux server)
DEFLATE, original name access.log, 512 KB uncompressed, ratio 0.08, OS Unix
Frequently asked questions
Is my file uploaded anywhere?
No. The .gz file is read and parsed entirely in your browser using JavaScript. Only the small header and footer are inspected and nothing is sent to a server, so private archives stay on your device.
Does it decompress the file?
No. Gzip records the original filename, modification time, source OS and the uncompressed size in a fixed header and footer. This tool reads those fields directly, so it works instantly even on huge archives without expanding them.
Why does the uncompressed size look wrong for a large file?
Gzip stores the uncompressed size as a 32-bit value, so it wraps around for files larger than 4 GB (it is the real size modulo 2^32). For files under 4 GB the value is exact.
What does the OS field mean?
The gzip header records which operating system created the archive, such as Unix, Windows (FAT), or Macintosh. A value of 255 means the creator left it unknown.
Why is there no original filename?
Storing the original filename is optional. If the FNAME flag is not set (common when piping data through gzip), the name was never recorded and the field is blank.
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