FormatFlow

Base64 Decoder: Decode Base64 Strings, UTF-8 Text & Files Online

Decode Base64 encoded strings and files with full Unicode (UTF-8) support. Includes auto-detection, URL-safe decoding, and image/PDF previews.

Base64 Input
Decoded Text
Drop file here or click to upload (up to 5 MB)

How to Use Base64 Decoder

  1. Paste your Base64 encoded string into the editor.
  2. Toggle URL-Safe mode (substituting + with - and / with _) for web safety.
  3. If decoding an image or PDF, view the automatic preview box below.
  4. Download the decoded payload or copy it to your clipboard with one click.

Practical Examples

Unicode & Emoji Round-trip

Multibyte characters and emojis are decoded safely without truncation.

Input:
SGVsbG8=
Output:
Hello

URL-Safe Base64

Replaces + with - and / with _ without padding.

Input:
héllo ✓
Output:
aMOpbGxvIOKchQ==

Common Mistakes & Troubleshooting

  • Using standard atob() on Unicode: Native JavaScript atob/btoa throws a CharacterOutofRange error on multibyte UTF-8 characters. FormatFlow uses a robust TextEncoder implementation that never crashes on emojis or accented characters.
  • Confusing standard Base64 with URL-safe Base64: URL-safe Base64 uses "-" and "_" to avoid URL query parameter conflicts.

Frequently Asked Questions

Is Base64 encryption or encoding?

Base64 is an encoding format, NOT encryption. It translates binary octets into a 64-character ASCII alphabet so data can safely pass through text-based protocols. Anyone can decode a Base64 string instantly without a key or password.

Why do Base64 strings end with "=" or "==" padding?

The "=" symbol serves as padding. Base64 processes data in 24-bit chunks (three 8-bit bytes converted to four 6-bit Base64 characters). If the final block has only 1 byte, two padding "=" characters are appended; if it has 2 bytes, one "=" is appended.

Does Base64 encoding increase file size?

Yes. Base64 expands file size by approximately 33% (a 4:3 byte ratio), because every 3 binary bytes are represented by 4 ASCII text characters.

Is this Base64 decoder UTF-8 safe?

Yes! FormatFlow uses TextEncoder and TextDecoder APIs to guarantee 100% accurate round-trip encoding and decoding of any Unicode characters, Asian scripts, and emojis without crashing.

Can I decode Base64 images directly?

Yes! When you paste a Base64 string representing an image (PNG, JPG, WEBP, GIF, SVG), FormatFlow automatically detects the magic bytes and previews the image.