FontPlop

FontPlop is a free font viewer and tester that runs in the browser. Drop in a TTF, OTF, WOFF or WOFF2 file to see glyphs and Unicode values, test your own text, and review OpenType features, variable axes, supported languages and metrics checks. The site states the font file never leaves your device. It also offers a webfont generator, converters and text style tools, with no sign-up.