Encode data as Ascii85 (base85), which packs 4 bytes into 5 characters for about 25 percent overhead versus the 33 percent of Base64. Used inside PDF and PostScript streams.
Show calculation steps
Processed privately in your browser — nothing you paste is uploaded, logged or stored.
Denser than Base64
Ascii85 packs four bytes into five characters, an overhead of 25 per cent against Base64’s 33. It achieves that by using a much larger alphabet — 85 printable characters — which is also why it is unsuitable for URLs and for anything that will pass through case folding or quoting.
Worked example
4 bytes → one 32-bit number → 5 base-85 digits four zero bytes → z (the shortcut) Adobe framing: <~ ... ~>
Where it is used
Inside PDF and PostScript, which is where most people meet it: embedded images and fonts in a PDF are frequently Ascii85. Adobe’s variant adds the <~ and ~> delimiters and the z shortcut, which collapses four zero bytes to one character and matters because runs of zeros are common in binary data.
The trade it makes
Eight per cent smaller than Base64 sounds marginal, and it is — until the payload is a multi-megabyte embedded font. The cost is an alphabet full of punctuation, which is exactly why Base64 remains the default everywhere the data has to pass through a URL, an email header or a shell.
Limits
An encoding, not compression and not protection: the output is fully reversible by anyone. Encoding happens in your browser.
How to use the Ascii85 Encoder
- Paste the text or data to encode.
- Turn on the delimiter option if the target format expects the Adobe style with opening and closing markers.
- Leave the z shortcut enabled unless the consumer of the data does not support it.
- Click "Encode to Ascii85".
Frequently asked questions
How much smaller is Ascii85 than Base64?
Ascii85 encodes four bytes as five characters, an overhead of 25 percent, against Base64 which encodes three bytes as four characters for 33 percent. On a large stream that difference is meaningful, which is why PDF uses it.
What does the "z" character mean in the output?
It is a shorthand for a group of four zero bytes, which would otherwise take five characters. Because runs of zero bytes are common in binary data, this small optimisation adds up. Some strict decoders do not accept it, so it can be turned off.
Where is Ascii85 used in practice?
Chiefly inside PDF and PostScript, where binary streams must be embedded in a text-based file format. It also appears in some version control and diff formats for the same reason.
Why does the encoded text contain punctuation and symbols?
The alphabet is 85 consecutive printable ASCII characters starting at the exclamation mark, so punctuation is unavoidable. That is also why Ascii85 is a poor fit for URLs and why Base64URL exists.
