What characters does Base91 use?

Base91 uses 91 printable ASCII characters: A-Z, a-z, 0-9, and a set of punctuation characters, excluding a few that cause issues in certain contexts such as the backslash.

How is Base91 more efficient than Base64?

Base91 encodes 13 bits per 2 output characters on average, resulting in roughly 23% size overhead. Base64 encodes 6 bits per character, resulting in 33% overhead. The difference is meaningful for large payloads.

Is this tool safe to use with sensitive data?

All encoding and decoding happens entirely in your browser using JavaScript. No data is transmitted to any server. You can use it offline once the page loads.

Can I decode any Base91 string here?

Yes, paste a valid Base91-encoded string into the input and click Decode. If the string contains invalid characters, an error will be shown.

Does Base91 support Unicode or binary data?

This tool encodes UTF-8 text. The input is first converted to UTF-8 bytes, then Base91-encoded. On decode, the bytes are interpreted as UTF-8. For raw binary files, use a dedicated binary encoder.

Base91 Encoder

Encode plain text or binary data to Base91, producing compact ASCII-safe output with ~23% overhead vs Base64's ~33%.

Input

Output

Summary

Base91 is an encoding scheme that converts binary data into a printable ASCII string using 91 safe characters. It produces roughly 23% overhead over the original data size, compared to Base64's 33% overhead, making it more space-efficient for transmitting or storing encoded data. This tool encodes and decodes text in your browser without sending data to any server.

How it works

Paste or type text into the input field.
Click Encode to convert your text to Base91 output.
Click Decode to reverse a Base91 string back to its original text.
Use the Copy button to copy the result to your clipboard.
All processing happens locally in your browser — no data leaves your device.

Use cases

Encoding binary payloads for ASCII-only transport protocols.
Reducing encoded data size compared to Base64.
Embedding data in environments that allow 91 printable ASCII characters.
Testing and verifying Base91-encoded strings during development.
Encoding configuration data or tokens for compact storage.
Decoding Base91 strings received from other systems.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu