Base64 Encoder

What this tool does

Base64 rewrites arbitrary bytes using only 64 characters that survive systems built for text. This encoder takes what you type — or a file you drop on it — and produces that representation, with control over the alphabet, the padding and the line width.

Non-ASCII input is handled properly. The text is encoded as UTF-8 first, so an em dash or an emoji becomes the right sequence of bytes rather than throwing the way the browser's own btoa() does on anything above U+00FF.

Common uses

• Embedding a small image or font directly in CSS or HTML as a data URI, removing one network round trip on a critical asset.
• Building an HTTP Basic credential: the header value is Basic followed by the Base64 of username:password.
• Putting binary into a JSON field, a YAML value or an environment variable, none of which can hold raw bytes.
• Encoding a certificate or key body for a Kubernetes secret, which expects Base64 values.
• Attaching a file to a MIME email body, where the 76-character line rule applies.

A short example

Three ASCII characters become four Base64 characters, exactly:

foo   →  Zm9v
fo    →  Zm8=
f     →  Zg==

And a character outside ASCII becomes its UTF-8 bytes first:

é  →  C3 A9  →  w6k=

Choosing the alphabet and the padding

The standard alphabet ends with + and /. Both have meaning inside a URL — + is a space in a form-encoded query, and / is a path separator — so RFC 4648 §5 defines a URL-safe variant that uses - and _ instead. Pick it whenever the value will appear in a path, a query parameter or a filename.

The trailing = characters pad the output to a multiple of four. They carry no data, and JSON Web Tokens omit them entirely. Turn padding off when the consumer expects it off; leave it on when you are not sure, since almost every decoder accepts padded input.

Line wrapping exists for the same historical reason: RFC 2045 limits an encoded MIME body to 76 characters per line. It is cosmetic — decoders ignore the newlines — but some older mail and PEM parsers insist on it.

Worth knowing

Base64 is an encoding, not encryption. Anyone can reverse it in one step, so it hides nothing. It also costs space: every three bytes become four characters, so the output is about 33% larger than the input, before line breaks. For a 2 MB image that is 700 KB of extra payload that cannot be cached separately from the document it sits in — which is why data URIs are worth it for icons and rarely worth it for photographs.