Base64 encoding explained — what it is and when to use it

Base64 converts binary data into text so it can be safely sent through systems that only handle text. Learn what it does and common uses.

What is Base64

Base64 is a binary-to-text encoding scheme that converts binary data into a sequence of printable ASCII characters. The name comes from the fact that it uses 64 different characters to represent data. It is defined in RFC 4648 and is one of the most widely used encoding standards in computing.

Why Base64 exists

Many systems and protocols were originally designed to handle only text. Email systems (SMTP), HTML, JSON, and XML all have restricted character sets. Binary data — like images, audio files, or executable code — contains bytes that are invalid in these contexts. Base64 solves this by representing every byte of binary data using only safe printable characters.

The Base64 character set

Base64 uses: A–Z (26 characters), a–z (26 characters), 0–9 (10 characters), + and / (2 characters) = 64 characters total. The = sign is used as padding. A URL-safe variant replaces + with - and / with _ to avoid conflicts in URLs.

Common real-world uses

• Data URIs: Embedding images in HTML or CSS without separate image files
• Email attachments: MIME encoding for file attachments in emails
• JSON APIs: Sending binary data (images, documents) in JSON payloads
• HTTP Basic Auth: username:password encoded in the Authorization header
• JWT tokens: The header and payload sections are Base64-encoded
• Fonts in CSS: Inline web fonts as Base64 in CSS @font-face

Base64 is not encryption

Base64 provides no security. It is trivially reversible without any key. Never use Base64 to "hide" sensitive data. For security, use proper encryption. For data integrity, use digital signatures or HMAC.

Try the Base64 Encoder Decoder tool to encode and decode text instantly in your browser.