Where SVGZ came from
SVGZ is simply an SVG run through gzip, typically cutting the file by 60-80% since XML compresses extremely well. It was more useful before web servers compressed responses on the fly; today it mostly turns up in design-tool exports and asset archives.
The technical picture
Compression: gzip-compressed XML. Transparency: Full alpha. Animation: Supported. Colour: Unlimited — resolution independent. Typical file size relative to WebP: tiny for flat graphics.
Where it opens
Browsers, when served with the right Content-Encoding. This is usually the deciding factor when choosing between SVGZ and WebP — WebP renders in every browser but is uneven in desktop software, while SVGZ has a very different support profile.
Converting SVGZ to WebP
Rasterising SVGZ to WebP produces a fixed-size image for destinations that cannot handle vectors, and sidesteps the Content-Encoding configuration SVGZ needs to display correctly in a browser. Rasterising is one-way. Keep the vector source for future resizes.
Converting WebP to SVGZ
Rarely needed — SVG is the usual target.. Expect the SVGZ output to be tiny for flat graphics — that difference is the price of getting a format the destination will actually accept.