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Base64 Encode/Decode

Encode text or files to Base64 and decode Base64 back instantly.

100% Private — Your files never leave your device.

All processing happens in your browser. Nothing is uploaded to any server.
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How it works

What Is Base64?

Base64 is a group of binary-to-text encoding schemes that represent binary data as an ASCII string. The name comes from the 64 characters in its alphabet:

  • 26 uppercase letters: A–Z
  • 26 lowercase letters: a–z
  • 10 digits: 0–9
  • 2 symbols: + and /
  • Padding character: =

How It Works

Base64 encoding takes every 3 bytes (24 bits) of input and splits them into 4 groups of 6 bits each. Each 6-bit group maps to one of the 64 characters. If the input length isn’t a multiple of 3, the output is padded with = characters.

Input:    M        a        n
ASCII:    77       97       110
Binary:   01001101 01100001 01101110
6-bit:    010011 010110 000101 101110
Base64:   T        W        F        u

Common Use Cases

Use CaseWhy Base64?
Email attachmentsSMTP only supports 7-bit ASCII. MIME encodes attachments as Base64.
Data URIsEmbed images directly in HTML/CSS without separate HTTP requests.
HTTP Basic AuthCredentials are Base64-encoded in the Authorization header.
JSON/XML payloadsSafely include binary data in text-only formats.
API tokensMany APIs encode token components as Base64 (e.g., JWT).

Base64 vs Other Encodings

EncodingAlphabet SizeOverheadUse Case
Base6464 chars~33%General binary-to-text
Base3232 chars~60%Case-insensitive contexts
Hex16 chars100%Debugging, hash display
URL encodingASCIIVariableURLs and query strings

Privacy & Security

All encoding and decoding happens entirely in your browser. No data is sent to any server. This tool uses the Web Crypto API’s TextEncoder and native btoa/atob functions — the same primitives used by your browser internally.

Real-World Examples

1

Encoding API credentials for HTTP headers

Mode: Encode Text: username:password123

A developer needs to send HTTP Basic Authentication credentials. The username:password pair is encoded to Base64 ('dXNlcm5hbWU6cGFzc3dvcmQxMjM=') and placed in the Authorization header as 'Basic dXNlcm5hbWU6cGFzc3dvcmQxMjM='. This is a standard requirement for REST APIs using Basic Auth.

2

Decoding a Base64-encoded email attachment

Mode: Decode Text: SGVsbG8gV29ybGQh

An email arrives with a Base64-encoded body (MIME encoding). Pasting the encoded string into the decoder instantly reveals the original text 'Hello World!'. MIME email encoding uses Base64 to safely transmit binary content through text-only email protocols.

3

Embedding a small image in CSS as a data URI

Mode: Encode (File) File: icon.png (2KB)

A web developer encodes a small PNG icon to Base64 to embed it directly in CSS as a data URI, eliminating an HTTP request. The 2KB PNG becomes approximately 2.7KB in Base64 (33% overhead), but saves a network round-trip. This technique is ideal for icons under 5KB.

Frequently Asked Questions

What is Base64 encoding?
Base64 is a binary-to-text encoding scheme that converts binary data into a string of 64 ASCII characters (A-Z, a-z, 0-9, +, /). It's used to safely transmit binary data through text-only channels like email (MIME), URLs, JSON, and HTML. The encoded output is approximately 33% larger than the input because every 3 bytes of input become 4 characters of output.
Why is Base64 needed?
Many protocols and formats only support ASCII text. If you need to include binary data (images, files, non-ASCII characters) in JSON, XML, email, or URL parameters, you must encode it as text first. Base64 provides a standard, safe way to do this. It's also used for HTTP Basic Authentication, data URIs in HTML/CSS, and storing binary data in databases that only support text.
Is Base64 encryption?
No. Base64 is encoding, not encryption. It provides no security whatsoever — anyone can decode a Base64 string instantly. It's a data format, like converting a number to hexadecimal. Never use Base64 to 'protect' passwords, API keys, or sensitive data. For actual security, use proper encryption (AES, RSA) or hashing (bcrypt, SHA-256).
What is the size overhead of Base64?
Base64 encoding increases data size by approximately 33%. Every 3 bytes of input produce 4 characters of output (plus padding). A 1MB file becomes roughly 1.33MB when Base64-encoded. This overhead matters for large files but is negligible for small strings. When line-wrapped (76 characters per line, MIME standard), the overhead increases slightly due to the added newline characters.
Does this tool handle Unicode and emoji?
Yes. This tool uses UTF-8 encoding before Base64 encoding, which correctly handles all Unicode characters including non-Latin scripts (Chinese, Japanese, Arabic, etc.) and emoji. The standard btoa() function in browsers only handles Latin-1 characters, but our implementation uses TextEncoder/TextDecoder for full Unicode support.
What is the difference between Base64 and Base64URL?
Standard Base64 uses '+' and '/' as the 63rd and 64th characters, with '=' for padding. Base64URL (used in JWTs and URLs) replaces '+' with '-' and '/' with '_', and often omits padding. This tool uses standard Base64 (RFC 4648). For JWT tokens, use our JWT Decoder tool which handles Base64URL automatically.

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