Base64 Converter

How Base64 Encoding Works (RFC 4648)

Computers store data as bytes (8 bits). Many communication channels, such as email protocols (MIME) and early networking layers, were designed strictly for 7-bit ASCII text and could corrupt control characters or raw byte values. Base64 solves this by mapping any arbitrary sequence of bytes into a safe alphabet of 64 printable ASCII characters:

• Uppercase letters: A–Z (indices 0–25)
• Lowercase letters: a–z (indices 26–51)
• Digits: 0–9 (indices 52–61)
• Symbols: + and / (indices 62 and 63)
• Padding: = (used when the input length is not a multiple of 3 bytes)

Every 3 bytes of binary input (3 × 8 = 24 bits) are divided into 4 groups of 6 bits (4 × 6 = 24 bits). Each 6-bit integer (value 0 to 63) indexes directly into the Base64 alphabet table.

Base64 vs. Base64URL: Key Differences

While standard Base64 works well for MIME email and general data storage, its reserved symbols cause issues inside URLs and HTTP headers. Here is how standard Base64 compares to URL-safe Base64:

How to Encode & Decode Base64 in Code

Common implementations across modern programming languages:

// Modern Browser (UTF-8 Safe)
const text = "Hello World! 🚀";
const encoded = btoa(unescape(encodeURIComponent(text)));
const decoded = decodeURIComponent(escape(atob(encoded)));

// Node.js
const nodeEncoded = Buffer.from("Hello World!", "utf-8").toString("base64");
const nodeDecoded = Buffer.from(nodeEncoded, "base64").toString("utf-8");

import base64

# Standard Base64 Encoding
raw_bytes = "Hello World!".encode("utf-8")
encoded_str = base64.b64encode(raw_bytes).decode("utf-8")  # "SGVsbG8gV29ybGQh"

# Standard Base64 Decoding
decoded_bytes = base64.b64decode(encoded_str)
decoded_str = decoded_bytes.decode("utf-8")  # "Hello World!"

package main

import (
    "encoding/base64"
    "fmt"
)

func main() {
    msg := "Hello World!"
    encoded := base64.StdEncoding.EncodeToString([]byte(msg))
    fmt.Println(encoded) // "SGVsbG8gV29ybGQh"

    decoded, _ := base64.StdEncoding.DecodeString(encoded)
    fmt.Println(string(decoded)) // "Hello World!"
}

Embedding Base64 Images as Data URLs

A Data URL allows binary assets (such as PNG or SVG icons) to be embedded directly inline inside HTML or CSS without an extra HTTP network request:

<!-- Embedding directly in an HTML image tag -->
<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAUA..." alt="Embedded Icon" />

/* Embedding directly inside a CSS stylesheet */
.icon {
  background-image: url("data:image/svg+xml;base64,PHN2ZyB4bWxucz0...");
}

Best Practice: Keep Base64 Data URLs below 10–15 KB. For larger images, external file URLs leverage HTTP caching, CDN delivery, and parallel downloads more efficiently.

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