Base85 Encoder Decoder
Encode and decode Base85 (Ascii85) - more compact than Base64
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About Base85 Encoder Decoder
Base85 Encoder Decoder - Maximum Density Binary-to-Text Encoding
The Base85 Encoder Decoder converts data between raw bytes and Base85 (also known as Ascii85) encoded text, offering the most space-efficient standard binary-to-text encoding available. If you need to embed binary data in text-based formats while minimizing size overhead, or if you work with PostScript, PDF internals, or Git binary patches, Base85 is your optimal choice and this tool makes it effortless to use.
Understanding Base85 Encoding
Base85 encodes four bytes of binary data into five ASCII characters, giving it a 4:5 expansion ratio - that is only 25 percent overhead. Compare this to Base64 at 3:4 (33 percent overhead) or hexadecimal at 1:2 (100 percent overhead). The improved efficiency comes from using a larger character set: 85 printable ASCII characters provide enough combinatorial space to represent any four-byte value in just five characters, since 85^5 (4,437,053,125) exceeds 2^32 (4,294,967,296).
The Base85 character set typically starts at ASCII 33 (exclamation mark) and runs through ASCII 117 (lowercase u), covering 85 consecutive printable characters. This range avoids spaces, control characters, and the DEL character, ensuring the encoded output is safe for inclusion in most text-based formats.
Ascii85 and Its Variants
The terms Base85 and Ascii85 are often used interchangeably, but there are actually several variants with subtle differences:
btoa/Ascii85: The original format, developed at Bell Labs, wraps encoded data between delimiters and uses z as a shorthand for four zero bytes (encoding 00000000 as a single z instead of five exclamation marks). This is the format used in PostScript and PDF.
Z85 (ZeroMQ Base85): Uses a different 85-character set that avoids characters problematic in certain contexts (no quotes, no backslash). Designed for embedding in source code and JSON strings. Used by the ZeroMQ messaging library.
RFC 1924 (IPv6 encoding): A semi-humorous RFC that proposed encoding IPv6 addresses in Base85 to make them shorter. Uses yet another character set. While never widely adopted for IPv6, the encoding itself is valid and occasionally used elsewhere.
This Base85 Encoder Decoder supports the standard Ascii85 format with the option to include or exclude the traditional delimiters.
Where Base85 Is Used in Practice
Adobe PostScript and PDF use Ascii85 encoding for embedded binary data (images, fonts, etc.) because it is more efficient than the hexadecimal encoding alternative while remaining fully text-safe. If you have ever opened a PostScript file in a text editor and seen streams of seemingly random characters between delimiters, you were likely looking at Ascii85-encoded data.
Git uses a variant of Base85 for encoding binary patches. When you run git diff on a binary file, the binary delta is Base85-encoded so it can be included in the text-based patch format. The btoa and atob Unix utilities (not to be confused with the JavaScript functions of the same name, which use Base64) implement Ascii85 encoding and decoding.
When to Choose Base85 Over Base64
If minimizing encoded size is your priority and your transport or storage medium can handle the full printable ASCII range, Base85 is the better choice. The 8 percentage point efficiency advantage over Base64 compounds meaningfully on large data - a 10 MB binary file encodes to approximately 12.5 MB in Base85 versus 13.3 MB in Base64. That is 800 KB saved.
However, if your encoded data needs to be URL-safe, included in XML attributes, or transmitted through systems that may not handle the full ASCII range, Base64 (especially URL-safe Base64) is the safer choice. Base85 includes characters like angle brackets, ampersands, and backslashes that are special in many contexts.
Using the Tool
Paste text or binary data to encode, or paste Base85-encoded text to decode. The Base85 Encoder Decoder handles the conversion instantly in your browser. The output can be copied with a single click, ready for inclusion in your PostScript files, development projects, or data pipelines.
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Everything runs locally. No data is transmitted, no accounts are required, and there are no usage restrictions. Encode and decode with complete confidence in your privacy.