Vector Tile styles require icons are served in a sprite sheet. This contains all of the icons in one file. Years ago there were a few options for these, none of them great. These days, there are three common options: spreet, @basemaps/sprites, and sprite-one. The first is written in Rust while the other two are written in Javascript.

All have the same basic functionality of turning a folder of SVGs into a json+png spritesheet, and doing so at multiple resolutions. Spreet has the additional option of de-duplicating icons. If two icons are identical it will only put one copy in the PNG and reference the same image twice.

I benchmarked all three options with two sets of sprites: all the SVGs from OpenStreetMap Carto, and the OpenStreetMap Americana icons. The former is 973 icons and the latter is 248 icons. These are larger than a typical set of icons but are a good test.

	Test	spreet	sprite-one	@basemaps/sprites
osm-carto SVGs	@1x pixels	4194304	4078074	8339456
osm-carto SVGs	@1x bytes	513159	763531	837792
osm-carto SVGs	@1x bytes after oxipng	474750	649894	706845
osm-carto SVGs	@2x bytes	1442588	2176457	2411489
osm-carto SVGs	@2x bytes after oxipng	1325707	1896784	2088729
osm-americana	@1x pixels	128265	122400	151760
osm-americana	@1x bytes	75749	91870	92066
osm-americana	@1x bytes after oxipng	75497	84986	85828
osm-americana	@2x bytes	136177	213876	210650
osm-americana	@2x bytes after oxipng	132462	197687	194950

I ran oxipng with oxipng -o max --strip all --alpha -i 0 -Z --fast spreet.png to recompress the PNG to be as small as possible. Spreet came out significantly ahead in file size and appears to have a better PNG encoder, as less space was saved by oxipng.