Base64 Encoding: What It Is and When to Use It
A developer-friendly guide to Base64 encoding, size overhead, data URLs, and common mistakes.
Base64 is encoding, not encryption
Base64 represents binary data using printable text characters. Anyone can decode it, so it must never be treated as a security control. Its purpose is safe transport through systems designed primarily for text.
Why the output gets larger
Base64 represents each three bytes of input with four text characters, plus possible padding. The encoded result is therefore roughly one third larger before any surrounding markup or protocol overhead.
Common uses
You may see Base64 in email attachments, API payloads, basic authorization headers, certificates, and data URLs. It is useful when a protocol cannot carry raw binary data cleanly, but separate files are often better for large web assets.
- Transporting small binary values in JSON
- Embedding tiny images in CSS or HTML
- Representing cryptographic bytes as text
Unicode and decoding errors
Text must first be converted to bytes using a character encoding such as UTF-8. Problems occur when the encoder and decoder assume different character encodings, when URL-safe and standard Base64 alphabets are mixed, or when padding is removed unexpectedly.