Your Base64 Decoding Failed Because of Whitespace (and 3 Other Silent Traps)

You paste a Base64 string into a decoder, and it throws InvalidCharacterError or returns garbage. Nine times out of ten the alphabet is fine — it's invisible whitespace, padding, or the URL-safe variant that broke it. Here are the four traps I hit most often, and how to spot each one in seconds. 1. Line breaks (the MIME 76-column wrap) Email-era encoders still wrap output at 76 characters with \r\n. Python's base64.encodebytes() does this, and so do PEM/JWKS files. atob() in the bro