Base64 Encoder / Decoder

What Is Base64 Encoding?

Base64 is a binary-to-text encoding scheme that represents binary data using a set of 64 ASCII characters (A-Z, a-z, 0-9, +, /). It is designed to carry data stored in binary formats across channels that only reliably support text content.

How Base64 Works

Base64 encoding takes every three bytes (24 bits) of input and splits them into four 6-bit groups. Each 6-bit value maps to one of the 64 characters in the Base64 alphabet. If the input length is not a multiple of three, padding characters (=) are added to the output.

Common Uses of Base64

• Data URIs: Embedding images, fonts, or other assets directly in CSS or HTML using data:image/png;base64,... eliminates extra HTTP requests.
• Email (MIME): Email protocols like SMTP are text-based, so binary attachments (images, PDFs) are Base64-encoded before transmission.
• API Authentication: HTTP Basic Authentication encodes username:password in Base64 before sending it in the Authorization header.
• JSON Payloads: When binary data needs to travel inside a JSON object (which only supports text), Base64 is the standard encoding.
• JWT Tokens: JSON Web Tokens encode their header and payload sections using Base64URL (a URL-safe variant).

Base64 and File Size

Base64 encoding increases data size by approximately 33% because three bytes of input become four bytes of output. This trade-off is acceptable for small assets but can be costly for large files. For images above a few kilobytes, serving them as separate files with proper caching is usually more efficient than inlining as Base64.

Unicode Support

The browser-native btoa() function only handles Latin-1 characters. To encode Unicode text (emojis, CJK characters, etc.), the input must first pass through TextEncoder to produce UTF-8 bytes, which are then Base64-encoded. This tool handles Unicode automatically.