Base64 Text Obfuscator with Custom Alphabet

Custom Base64 obfuscation is a technique that modifies the standard Base64 encoding scheme by replacing its well-known alphabet with a shuffled or user-defined 64-character set. Standard Base64 uses the alphabet A-Za-z0-9+/ — 64 characters total — to represent binary data as text. A custom Base64 alphabet replaces these 64 characters with a different ordering, so the encoded output looks like valid Base64 but cannot be decoded by standard tools.

For example, encoding "Hello" with standard Base64 produces SGVsbG8=. With a custom alphabet where A and Z are swapped, the output would be completely different (e.g., ZHWsaWw9). Someone running the standard Base64 decoder on the custom output will get garbled data or an error, making this a lightweight but effective obfuscation technique.

1. 1. Set Your Alphabet: Enter a custom 64-character alphabet in the alphabet editor. Each character must be unique and drawn from the standard Base64 character set (A-Z, a-z, 0-9, +, /). Use the Randomize button to generate a shuffled alphabet, or manually type your own. The alphabet mapping table shows which characters differ from the standard Base64 alphabet, highlighted in green.
2. 2. Encode or Decode: Select Encode mode to convert plain text into custom Base64, or Decode mode to convert custom Base64 back to plain text. The same alphabet must be used for both encoding and decoding. Toggle padding on/off with the = Padding button.
3. 3. Compare & Verify: Use the side-by-side comparison view to see how your custom Base64 output differs from standard Base64 encoding. Copy the encoded output and share only the alphabet with authorized recipients so they can decode it. Share the encoded data publicly — only those with the custom alphabet can read it.

• 64-Character Alphabet: A valid Base64 alphabet must have exactly 64 unique characters drawn from A-Z, a-z, 0-9, +, and /. Our tool enforces this constraint and shows a warning if your alphabet is incomplete.
• Padding (=): Standard Base64 uses = padding to ensure the output length is a multiple of 4. You can toggle padding on or off, though omitting it may produce slightly shorter output at the cost of standards compatibility.
• Not Encryption: Custom Base64 is obfuscation, not encryption. The data is encoded, not encrypted — anyone who knows the custom alphabet can decode it. Use proper encryption (e.g., AES) for sensitive data. Custom Base64 is best for preventing casual or automated decoding.
• Size Overhead: Like standard Base64, custom Base64 adds approximately 33% size overhead to the encoded output. This is because every 3 bytes of input are encoded into 4 Base64 characters.
• Deterministic: Given the same input text and the same custom alphabet, the encoded output is always identical. This makes it suitable for scenarios where reproducible encoding is important (e.g., caching, signing).

This Base64 Text Obfuscator with Custom Alphabet is 100% free with no signup required. All text processing is performedlocally in your browser — your text, custom alphabet, and encoded output never leave your device. There are no text length limits or usage caps. The tool includes a random alphabet generator, alphabet mapping table with position-level comparison to standard Base64, encode and decode modes, padding toggle, example presets, and works completely offline after the first load. Unlike standard Base64 decoders available everywhere, only this tool (or someone with your exact alphabet) can decode your custom Base64 data.