Web developers use base64 formats to include images, fonts, sounds, and other resources directly inside HTML, JavaScript, JSON, and XML files. We estimate that billions of base64 messages are decoded every day. We are motivated to improve the efficiency of base64 encoding and decoding. Compared to state-of-the-art implementations, we multiply the speeds of both the encoding (≈ 10 ×0) and the decoding (≈ 7 ×). We achieve these good results by using the single-instruction-multiple-data instructions available on recent Intel processors (AVX2). Our accelerated software abides by the specification and reports errors when encountering characters outside of the base64 set. It is available online as free software under a liberal license.