Why base64 content transfer encoding?
Base64 Content-Transfer-Encoding is one of the most common tasks developers hit when working with APIs, files, email attachments, and data URIs.
More Base64 guides on base64app — with copy-paste code and a free browser tool you can use without installing anything.
Quick reference
Base64 maps every 3 bytes to 4 ASCII characters. Padding with = may appear at the end. URL-safe variants swap +/ for -_.
When in doubt, paste your string into the tool below — base64app auto-repairs whitespace, data: prefixes, and padding issues.
Copy-paste code
MIME Content-Transfer-Encoding
Content-Type: application/pdf; name="file.pdf"
Content-Transfer-Encoding: base64
JVBERi0xLjQKJeLjz9MK...