What is Ascii85 used for?

Ascii85, also called Base85 or a85, is the binary-to-text encoding used inside PDF and PostScript files to embed images and other binary streams as printable text. It is about 25 percent more compact than Base64 because it packs four bytes into five characters instead of three bytes into four.

What does the single z character mean?

As a space-saving shortcut, a group of four zero bytes is written as the single character z instead of the five characters it would otherwise need. The decoder expands z back into four zero bytes, but only when it appears on a clean group boundary.

What are the angle-tilde delimiters around some Ascii85 data?

Inside a PDF, an Ascii85 stream is wrapped between an opening less-than-tilde and a closing tilde-greater-than. They mark where the encoded data starts and ends. This tool can add them on encode and strips them automatically on decode, so you can paste a stream with or without the framing.

How are partial final groups handled?

If the input length is not a multiple of four, the last group is conceptually padded with zero bytes, encoded, and then truncated so it emits one more character than the number of real bytes. The decoder reverses this, padding with the highest digit before discarding the extra byte, so the original length is preserved exactly.

Does this run locally?

Yes. All encoding and decoding happen in your browser, so the binary you paste — including data extracted from PDFs — never leaves your device.

Base85 / Ascii85 Encoder/Decoder

Ascii85 (also written Base85 or a85) is the binary-to-text encoding used in PDF and PostScript streams. By mapping four bytes onto five printable characters it is noticeably denser than Base64, which makes embedded images and fonts smaller. This tool encodes UTF-8 text into Ascii85 and decodes it back, including the z shortcut and optional PDF framing, all in your browser.

How it works

Ascii85 works on four-byte groups using base 85 with an offset:

Four bytes form a 32-bit number. That number is written as five base-85 digits, each offset by 33 so the characters fall in the printable range starting at !.
A full group of four zero bytes is collapsed to the single character z to save space.
A partial final group is padded with zero bytes to length four, encoded, then truncated so it emits exactly one more character than the number of real bytes.

Decoding reverses each step: every five characters rebuild a 32-bit value and therefore four bytes, z expands to four zero bytes, and a short final group is padded with the highest digit u before the surplus byte is dropped. Optional <~ and ~> delimiters are stripped automatically.

Tips and example

Encoding the four bytes of Man yields 9jqo^, the classic Ascii85 example. A run of zero bytes — common in binary headers — compresses dramatically thanks to the z shortcut. When you copy a stream out of a PDF it usually carries the <~ ... ~> framing; paste it as-is and the decoder will discard the delimiters. Note that Ascii85 is the Adobe variant; for the ZeroMQ-flavoured Base85 that is safe inside source-code strings, use the dedicated Z85 tool instead.