How to check if a file is gzip compressed?

It is performing good with Google PageSpeed and GT Metrix, but Pingdom Tools keep complaining that gzip is not enabled. I have enabled Brotli, but is there a ...

I need to detect GZip file format by its content, not just file extension, using this code recently given.

Using MyGZipStream As New Compression.GZipStream(MyImportStream, Compression.CompressionMode.Decompress, False) Try MyGZipStream.

In order to detect if a file is gzipped, you can read the magic number at the beginning of the file, which is 1f 8b according to the link.

The magic number for gzip compressed files is 1f 8b. Although testing for this is not 100% reliable, it is highly unlikely that ordinary text files start with ...

You can check the header of the HTTP connection. If the header containg the field Content-Encoding: gzip the content is gzipped.

Media type detection. ... This is designed to detect commonly gzipped file types such as warc.gz. Copyright © 2007–2025 The Apache Software Foundation. All ...

The gzip -t command only returns an exit code to the shell saying whether the file passed the integrity test or not. Example (in a script):

gzip is guaranteed to detect a truncated input if the size of the compressed data (or the size of the decompressed data) is less than 4 GiB.

This test will check whether your website (and ultimately the server your website is hosted on) has Gzip or brotli enabled by connecting to your domain.