Base64 Encode & Decode — Free Online Tool

Last Updated: April 1, 2026

Last updated: 2026-03-18

Base64 is everywhere in web development and most developers use it without fully understanding what it does or why. Here is the practical guide.

What Base64 Actually Does

Base64 converts binary data into a text string using 64 ASCII characters (A-Z, a-z, 0-9, +, /). This lets you embed binary data (images, files, encrypted content) in text-only contexts like JSON, XML, HTML, email, and URLs.

The 33% Size Increase

Base64 encoding increases data size by approximately 33%. Every 3 bytes of input become 4 bytes of output. This is why you should NOT Base64-encode large files — a 1MB image becomes 1.33MB as Base64 text, and the browser still has to decode it. For images larger than 2-3KB, a separate file with proper caching is more efficient.

Base64 vs Base64URL

Standard Base64 uses + and / which are special characters in URLs. Base64URL replaces them with - and _ and removes padding =. JWT tokens use Base64URL.

Related Tools

According to RFC 4648, Base64 encoding is defined with specific alphabets for standard and URL-safe variants.

As MDN Web Docs explains, Base64 is commonly used in web development for data URIs and API authentication.