Base64 Encode String — Convert Any String to Base64

Encoding Strings to Base64: The Complete Guide

Converting a string to Base64 is one of the most common encoding operations in modern web development. You need it when embedding text-based secrets in URLs, sending structured data across text-only transports, storing binary-looking blobs in config files, or building your own JWT-style tokens. This guide covers everything: the concept, worked examples in every major language, the UTF-8 pitfall, and when NOT to use Base64.

The UTF-8 Pitfall Every Developer Hits

Every JavaScript developer who tries to Base64-encode a Chinese character or emoji using the built-in btoa() function gets this error:

btoa('Hello 世界');
// Uncaught InvalidCharacterError: Failed to execute 'btoa' on 'Window':
// The string to be encoded contains characters outside of the Latin1 range.

The reason: btoa() was designed in 1995 for Latin-1 (single-byte) text. Any character with a code point above 255 breaks it. The fix — used by every modern encoder including the PromptSpace tool above — is to first convert the string to UTF-8 bytes, then Base64-encode those bytes:

function stringToBase64(str) {
  const utf8Bytes = new TextEncoder().encode(str);          // string → Uint8Array
  const binString = String.fromCharCode(...utf8Bytes);      // bytes → binary string
  return btoa(binString);                                    // binary string → Base64
}

stringToBase64('Hello 世界');  // "SGVsbG8g5LiW55WM"
stringToBase64('👋 Hi');       // "8J+RiyBIaQ=="

String-to-Base64 in Every Major Language

Python

import base64

# Python strings are Unicode by default — encode to bytes first
text = 'Hello 世界'
encoded = base64.b64encode(text.encode('utf-8')).decode('ascii')
print(encoded)  # "SGVsbG8g5LiW55WM"

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

Go

import (
    "encoding/base64"
    "fmt"
)

func main() {
    text := "Hello 世界"
    encoded := base64.StdEncoding.EncodeToString([]byte(text))
    fmt.Println(encoded)  // "SGVsbG8g5LiW55WM"
}

Rust

use base64::{Engine as _, engine::general_purpose::STANDARD};

fn main() {
    let text = "Hello 世界";
    let encoded = STANDARD.encode(text.as_bytes());
    println!("{}", encoded);  // "SGVsbG8g5LiW55WM"
}

Java

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

String text = "Hello 世界";
String encoded = Base64.getEncoder().encodeToString(text.getBytes(StandardCharsets.UTF_8));
System.out.println(encoded);  // "SGVsbG8g5LiW55WM"

PHP

$text = 'Hello 世界';
$encoded = base64_encode($text);  // PHP handles UTF-8 natively
echo $encoded;  // "SGVsbG8g5LiW55WM"

When to Encode a String to Base64

• URL parameters — pack a JSON blob into a single query string param
• Cookies — store structured data in a cookie value without picking a delimiter
• Environment variables — inject multi-line secrets (PEM keys, JSON) into a single env var
• HTTP Basic Auth — the user:pass string is Base64-encoded in the Authorization header
• JWT payloads — the JSON header and payload are Base64URL-encoded segments of a JWT
• Data URLs — embed a text blob (SVG, HTML, CSS) directly in an HTML attribute
• Config files — put binary-looking content into a YAML/TOML file that only accepts strings

When NOT to Encode a String to Base64

Base64 is NOT compression, NOT encryption, and NOT authentication. Never use it for:

• Hiding passwords or API keys — decoders are one line of code in every language
• Reducing size — Base64 makes strings 33% larger, not smaller
• Detecting tampering — anyone can decode, modify, and re-encode
• Storing plain text — if a plain string works, use it; Base64 adds noise for no reason

Key Facts

Input:

Any string — ASCII, UTF-8, Unicode, multi-line, JSON

Output size:

Approximately 4/3 the UTF-8 byte length of the input

Character encoding:

UTF-8 (safe for all Unicode)

Reversible:

Yes — lossless round-trip

Runs where:

Fully in your browser — no upload

Related Base64 Tools

• Base64 Encode Online — general-purpose encoder with URL-safe option
• Text to Base64 Converter — plain-text focused conversion guide
• Base64 Encode in JavaScript — deep dive on btoa, TextEncoder, and Buffer
• Base64 Encode in Python — b64encode with UTF-8 examples
• Base64 Decode — decode a Base64 string back to text
• URL Encoder — percent-encode strings for URLs