Base64 Encoder

Which text variant to use

Standard is RFC 4648 Base64, and what almost everything means by the word. Use it unless the destination tells you otherwise.

URL-safe swaps the two characters that cause trouble in a URL or filename — + and / — for - and _. It matters because standard Base64 in a query string gets mangled: a + is commonly read as a space, and a / can be taken for a path separator. If your encoded value is going into a URL, a cookie, a filename or a JWT, use this one.

MIME is standard Base64 broken into 76-character lines. Old email systems and some certificate formats require the line breaks and will reject one unbroken string. If you are pasting into a mail header or a PEM-style block, this is the variant.

Data URLs: the reason most people are here

Encode a file and you can have the raw Base64 or a Data URL, which is the same data with its type prefixed — data:image/png;base64,… — so it can be pasted directly wherever a file path would go. A small icon becomes a CSS background-image with no separate request, a logo travels inside an HTML email template rather than being blocked as a remote image, and a test fixture can hold its own sample file.

Keep it to small files. Base64 makes data about a third larger, and that inflated text sits inside your stylesheet or HTML where it cannot be cached separately, so a large embedded image makes the page slower rather than faster. Under a few kilobytes is a reasonable rule; past that, a normal file reference wins.

Encoding is not encryption

Worth stating plainly, because it is a recurring and costly misunderstanding. Base64 is a reversible way of writing binary data in plain text characters. It provides no secrecy at all — anyone can decode it instantly, with no key and no effort. It exists so that data survives systems that only handle text, not to hide anything. Never treat a Base64 string as a protected secret, and never store a password that way.

Nothing leaves your device

The file is read and encoded in the page itself, with no upload. For developers that is the whole argument: encoding a private key, a certificate or an internal asset on a site that uploads it to somebody's server is a habit worth not having, even when the server almost certainly discards it.

Related tools

Base64 Decoder goes the other way, turning a Base64 string back into text or a file. URL Encoder / Decoder handles percent-encoding for query strings, and Hash Generator produces MD5 and SHA hashes when you need a checksum rather than a reversible encoding.