That's not how ligatures work. You have to explicitly turn open type features on, they aren't automatic. They are additions to the character set. Edit: Unless

That's not how ligatures work. You have to explicitly turn open type features on, they aren't automatic. They are additions to the character set. Edit: Unless your reason for checking is that you explicitly want a marginally smaller file (possibly just at bytes level) to download (in which case just use one of the many online tools providing subsetting to strip unicode ranges and do something like remove everything except basic ascii?) there's no real point filtering for fonts without ligatures because, practically, that's just all of them