Kepler is a serif font. It goes well with Proxima Nova, Soleil, Leitura News, Avant Garde Gothic ITC, SS Standard, Futura PT, Menlo, Europa, Times and SS Social. If you're thinking about using Kepler then try 54px for headers. Give 18px a shot for content.
People commonly tag it as tech, event, bold, blog, design, clean, serif, agency, big and contrast. You can get it from Adobe Fonts, Fonts.com, Fontspring and Typekit.