What Is Base64 Encoding?

Why Base64 Exists

Many communication channels — email (SMTP), HTML, JSON, URLs — were designed to handle plain text only. Binary files (images, PDFs, certificates) contain arbitrary byte values including null bytes and control characters that break these channels. Base64 solves this by encoding any binary data into a safe 64-character alphabet.

The Base64 Alphabet

How Encoding Works

Base64 in Practice

• Data URIs: Embed images directly in HTML/CSS: src="data:image/png;base64,iVBOR..."
• JWT tokens: The header and payload sections are Base64URL encoded (uses - and _ instead of + and /).
• Email attachments: MIME attachments are Base64 encoded before transmission.
• API authentication: Basic Auth sends username:password as Base64.

Base64 Is NOT Encryption

This is the most common misconception. Base64 is an encoding, not encryption. It is completely reversible with zero secret keys. Never use it to secure sensitive data. Use TLS, AES, or bcrypt for security.

Size Overhead

Base64 increases data size by approximately 33% (4 output bytes per 3 input bytes). This is the trade-off for text-safe transmission.