How to Convert Base64 to Text

What is Base64 Encoding?

Base64 is a binary-to-text encoding scheme that represents binary data in an ASCII string format. It converts binary data into a set of 64 characters (hence the name "Base64") that can be safely transmitted over media designed for textual data. These 64 characters consist of uppercase letters A-Z, lowercase letters a-z, numbers 0-9, and the symbols '+' and '/' (with '=' used for padding).

When binary data needs to be stored or transferred over media that is designed to handle text (like email systems or APIs), Base64 encoding provides a way to convert that binary data into a text format. This is why you'll often see Base64-encoded strings in various technical contexts, from email attachments to web tokens and data URIs.

Why Would You Need to Decode Base64?

There are numerous scenarios where you might encounter Base64-encoded strings and need to convert them back to their original form:

• Working with APIs - Many APIs transmit data in Base64 format, especially for binary content like images or files.
• Email attachments - Files attached to emails are often Base64-encoded within the MIME format.
• Web development - Base64 strings are used in data URIs for embedding images directly in HTML/CSS.
• JWT (JSON Web Tokens) - Used for authentication, these tokens contain Base64-encoded segments.
• Decoding headers and signatures - Various security implementations use Base64 for encoding certificates and signatures.
• Analyzing encoded data - Security professionals often need to decode suspicious Base64 strings in logs or network traffic.

Converting Base64 back to text (or other forms of data) allows you to read, modify, or use the original information in its intended format.

Using an Online Base64 to Text Converter

The easiest and most straightforward way to decode Base64 is to use an online conversion tool. Here's how to use our Base64 decoder:

1. Go to Base64Converter.org
2. Click on the "Decode" tab (it should be the second tab at the top)
3. Paste your Base64-encoded string into the input field
4. The decoded text will automatically appear in the output field
5. Click "Copy to Clipboard" if you want to use the decoded text elsewhere

Special Options for Base64 Decoding

When decoding Base64, you might need to consider these options:

• URL-safe Base64 - If you're working with Base64 that was used in URLs, it might use '-' and '_' instead of '+' and '/'. Our tool has an option to handle URL-safe Base64.
• Padding - Standard Base64 uses '=' characters at the end for padding. Some implementations might omit these, but our decoder can handle Base64 strings with or without padding.
• Line breaks - Some Base64 implementations insert line breaks (usually every 76 characters). Our tool automatically removes these before decoding.

Manual Base64 Decoding: Step-by-Step

While online tools are convenient, understanding how Base64 decoding works can be valuable. Here's a simplified explanation of the manual decoding process:

1. Character to Value Mapping - Each Base64 character maps to a 6-bit value (0-63).
2. Grouping Bits - Four Base64 characters (24 bits) are decoded into three 8-bit bytes.
3. Handling Padding - '=' characters indicate that the final group has fewer than three bytes.

Decoding Base64 in Different Programming Languages

Most programming languages provide built-in functions or libraries for Base64 decoding. Here are examples in some popular languages:

JavaScript

// Decode Base64 to text
const decodedText = atob('SGVsbG8gV29ybGQh');
console.log(decodedText); // Output: Hello World!

// For Unicode strings, use this approach:
function decodeBase64(str) {
  return decodeURIComponent(atob(str).split('').map(function(c) {
    return '%' + ('00' + c.charCodeAt(0).toString(16)).slice(-2);
  }).join(''));
}

// Decode Base64 to binary (Uint8Array)
function base64ToUint8Array(base64) {
  const binary = atob(base64);
  const bytes = new Uint8Array(binary.length);
  for (let i = 0; i < binary.length; i++) {
    bytes[i] = binary.charCodeAt(i);
  }
  return bytes;
}

Python

import base64

# Decode Base64 to text
encoded = "SGVsbG8gV29ybGQh"
decoded_bytes = base64.b64decode(encoded)
decoded_text = decoded_bytes.decode('utf-8')
print(decoded_text)  # Output: Hello World!

# URL-safe Base64 decoding
url_safe_encoded = "SGVsbG8gV29ybGQh"
decoded_bytes = base64.urlsafe_b64decode(url_safe_encoded)
decoded_text = decoded_bytes.decode('utf-8')

PHP

<?php
// Decode Base64 to text
$encoded = "SGVsbG8gV29ybGQh";
$decoded = base64_decode($encoded);
echo $decoded;  // Output: Hello World!

// If handling binary data
$binary_data = base64_decode($encoded, true);
?>

Java

import java.util.Base64;

public class Base64Example {
    public static void main(String[] args) {
        // Decode Base64 to text
        String encoded = "SGVsbG8gV29ybGQh";
        byte[] decodedBytes = Base64.getDecoder().decode(encoded);
        String decodedText = new String(decodedBytes);
        System.out.println(decodedText);  // Output: Hello World!
        
        // URL-safe Base64 decoding
        String urlSafeEncoded = "SGVsbG8gV29ybGQh";
        byte[] urlDecodedBytes = Base64.getUrlDecoder().decode(urlSafeEncoded);
        String urlDecodedText = new String(urlDecodedBytes);
    }
}

Common Issues and Troubleshooting

When converting Base64 to text, you might encounter these common issues:

Invalid Base64 Input

If your Base64 string contains characters outside the Base64 alphabet (A-Z, a-z, 0-9, +, /, =), you'll get decoding errors. Check for:

• Accidental whitespace or newline characters
• Special characters that aren't part of Base64
• Truncated strings (incomplete Base64)

Padding Issues

Base64 strings should be padded with '=' characters to make their length a multiple of 4. Some implementations might omit padding or add incorrect padding, causing decoding errors.

URL-Safe vs. Standard Base64

If you're trying to decode a URL-safe Base64 string (using '-' and '_' instead of '+' and '/') with a standard decoder, you'll get incorrect results. Make sure you're using the right decoding mode.

Encoding Mismatch

If the decoded output looks like gibberish, there might be an encoding mismatch. The original data might have been in UTF-8, ISO-8859-1, or another character encoding that doesn't match your decoder's expected output encoding.

Practical Examples of Base64 Decoding

Decoding a JWT Token

JSON Web Tokens (JWT) consist of three Base64Url-encoded parts separated by dots. Here's how to decode the payload:

Decoding an Email Attachment

Email attachments in MIME format use Base64 encoding. Here's a simplified example:

Decoding a Data URI

Data URIs embed files directly in HTML/CSS using Base64 encoding:

Frequently Asked Questions