Base64 Encode

Related

What is Base64 Encoding?

Use Cases

• JWT debugging: decode the header and payload segments of a JWT (Base64URL format) to inspect the token's claims
• Basic Auth: encode a username:password pair into an HTTP Basic authentication credential
• OAuth development: generate the code_verifier for PKCE flows or verify an incoming code_challenge
• API debugging: encode JSON payloads or decode Base64 fields returned by an API
• Data URI image embedding: convert small icons into data:image/...;base64,... format to embed directly in CSS or HTML
• Email attachment encoding: encode binary email attachments in the MIME Base64 format

How to Use

1. Choose a mode: click Encode or Decode to switch the processing direction
2. Pick a variant: Standard, URL-Safe (for JWT / OAuth), or MIME (76-char email-format line wrapping)
3. Enter content: paste text or a Base64 string and the tool processes it in real time
4. Review stats: the bottom panel shows the character counts and the size overhead (about +33% for encoding)
5. Copy the result: one click copies the Base64 string or the decoded text to your clipboard

Features

• One-click Encode / Decode toggle: switch freely between encoding and decoding modes, with the output becoming the next input for circular processing
• Three charset support: UTF-8 (Chinese / Japanese / emoji), ASCII, and ISO-8859-1 for professional-grade multi-scenario coverage
• Three output variants: Standard, URL-Safe (for JWT / OAuth / PKCE), and MIME (RFC 2045 compliant 76-character line wrapping)
• Real-time size statistics: live input / output character counts and overhead ratio (Base64 grows the payload by ~33%)
• Friendly error messages: clear, specific errors when characters fall outside the valid range instead of a generic failure
• Draggable divider on desktop: adjust the left / right editor ratio to focus on the current task
• Independent mobile tabs: phones and tablets get separate tabs for the input and output panels, keeping the workflow smooth

Code Examples

// Encode (supports UTF-8)
function b64Encode(str) {
  return btoa(unescape(encodeURIComponent(str)));
}

// Decode (supports UTF-8)
function b64Decode(str) {
  return decodeURIComponent(escape(atob(str)));
}

// URL-Safe encode (for JWT / OAuth)
function b64UrlEncode(str) {
  return btoa(unescape(encodeURIComponent(str)))
    .replace(/\+/g, '-')
    .replace(/\//g, '_')
    .replace(/=+$/, '');
}

console.log(b64Encode('Hello 世界')); // SGVsbG8g5LiW55WM
console.log(b64Decode('SGVsbG8g5LiW55WM')); // Hello 世界

import base64

# Standard encode (UTF-8)
encoded = base64.b64encode('Hello 世界'.encode('utf-8'))
print(encoded.decode())  # SGVsbG8g5LiW55WM

# Standard decode
decoded = base64.b64decode(encoded).decode('utf-8')
print(decoded)  # Hello 世界

# URL-Safe encode (for JWT / OAuth)
url_safe = base64.urlsafe_b64encode('Hello 世界'.encode('utf-8'))
print(url_safe.decode())  # SGVsbG8g5LiW55WM (no padding — strip manually)

# Strip padding (JWT convention)
url_safe_no_pad = url_safe.decode().rstrip('=')
print(url_safe_no_pad)

import java.nio.charset.StandardCharsets;
import java.util.Base64;

public class Base64Example {
    public static void main(String[] args) {
        String text = "Hello 世界";

        // Standard encode
        String encoded = Base64.getEncoder()
            .encodeToString(text.getBytes(StandardCharsets.UTF_8));
        System.out.println(encoded); // SGVsbG8g5LiW55WM

        // Standard decode
        String decoded = new String(
            Base64.getDecoder().decode(encoded), StandardCharsets.UTF_8);
        System.out.println(decoded); // Hello 世界

        // URL-Safe encode (for JWT / URL)
        String urlSafe = Base64.getUrlEncoder().withoutPadding()
            .encodeToString(text.getBytes(StandardCharsets.UTF_8));
        System.out.println(urlSafe);

        // MIME encode (76-char line wrapping)
        String mime = Base64.getMimeEncoder()
            .encodeToString(text.getBytes(StandardCharsets.UTF_8));
    }
}

FAQ

Glossary

RFC 4648

The IETF official standard for Base16 / Base32 / Base64 encodings, defining the Standard and URL-Safe Base64 alphabets along with rules for padding, line breaks, and non-alphabet characters. It is the de facto Base64 standard today and supersedes the earlier RFC 3548.URL-Safe Base64 ToolBase64 Padding Tool

RFC 2045 (MIME)

The Multipurpose Internet Mail Extensions (MIME) standard, which first introduced Base64 as a content transfer encoding for email. It requires that Base64 output use lines of no more than 76 characters separated by CRLF, giving rise to the MIME Base64 variant.MIME Base64 Tool

Base64URL (URL-Safe Base64)

The URL-safe variant defined in RFC 4648 §5. It replaces the + with - and / with _ from the standard Base64 alphabet, and usually omits the = padding. It is widely used for JWT tokens, OAuth PKCE values, URL parameters, and file names.URL-Safe Base64 ToolJWT Tool

MIME Base64

A Base64 variant that complies with RFC 2045, inserting a CRLF line break every 76 characters. It is mainly used for email attachment transmission, because older SMTP protocols impose a limit on the length of a single line.MIME Base64 Tool

Padding

Base64-encoded output length must be a multiple of 4. When the input byte count is not a multiple of 3, the end is padded with = characters. Standard Base64 uses padding, while Base64URL usually omits it.Base64 Padding Tool

Base64 Alphabet

The set of 64 characters used in Base64 encoding. The standard Base64 alphabet is A-Z (26), a-z (26), 0-9 (10), +, and /, totaling 64 characters, plus the = padding character.Base64 Encode

btoa / atob

Native browser APIs for Base64 encoding and decoding. btoa (binary to ASCII) encodes, atob (ASCII to binary) decodes. Note that these APIs only support the Latin-1 character set, so handling Chinese text requires pairing them with UTF-8 transcoding.Base64 Encode

Data URI Scheme

A URI format that allows small files to be embedded directly inside a URL, written as data:[<mediatype>][;base64],<data>. It is commonly used to inline small icons and CSS background images to reduce HTTP requests.Data URI ToolBase64 to Image

HTTP Basic Authentication

An HTTP authentication scheme that joins the username and password with a colon, Base64-encodes the result, and sends it in the Authorization request header. The format is: Authorization: Basic <base64(username:password)>.Auth Header Builder

Base64 Overhead

The percentage by which Base64 encoding grows the data. Every 3 bytes (24 bits) becomes 4 Base64 characters, so the payload grows by about 33% (4/3 ≈ 1.333). The overhead can be slightly higher when padding is included.

Base64 Variant Comparison

Base Encoding Family Comparison

Authoritative References

• ReferenceRFC 4648 - The Base16, Base32, and Base64 Data Encodings
• ReferenceRFC 2045 - MIME Part One: Format of Internet Message Bodies
• ReferenceRFC 7519 - JSON Web Token (JWT)
• ReferenceMDN Web Docs - btoa()
• ReferenceMDN Web Docs - atob()
• ReferenceWikipedia - Base64