Base64 Encoder/Decoder

What is Base64?

Base64 is a binary-to-text encoding scheme that represents binary data using 64 printable ASCII characters (A–Z, a–z, 0–9, +, /). It's used whenever binary data needs to pass through systems designed for text — email, JSON payloads, HTML attributes, and URLs.

The encoding increases size by roughly 33% (every 3 bytes of input becomes 4 characters of output), which is why it should only be used for transport, not storage.

Common use cases

Email attachments (MIME)

SMTP only supports 7-bit ASCII. Base64 encoding lets binary attachments (images, PDFs) travel safely through email servers.

Data URIs

Embed small images directly in HTML or CSS using data:image/png;base64,... to avoid extra HTTP requests.

API authentication

HTTP Basic Authentication encodes username:password as Base64 in the Authorization header. Note: this is encoding, not encryption — it provides no security on its own.

JWT tokens

JSON Web Tokens use URL-safe Base64 to encode the header and payload sections.

Configuration files

Kubernetes Secrets, SSH keys in CI/CD, and certificate PEM files all use Base64 encoding.

URL-safe Base64

Standard Base64 uses + and /, which have special meaning in URLs and filenames. The URL-safe variant (RFC 4648 §5) replaces them:

• + becomes -
• / becomes _
• Trailing = padding is stripped

Use URL-safe encoding for JWT tokens, URL parameters, and filename-safe identifiers.

UTF-8 handling

The browser's native btoa() function only handles Latin-1 characters and throws on anything outside that range (like emoji or CJK characters). This tool uses a UTF-8 encoding step first, so characters like 日本語 and 🚀 encode and decode correctly.