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And this is what I've been spending my evenings on lately. A decoder for receipt printer protocols. You can take the bytes that get send to a receipt printer and inspect the commands that are inside of it. And... actually see a render of the receipt. Only useful for a hand full of people. And me.

But let's rewind. You start with some JavaScript and my ReceiptPrinterEncoder library to create the actual receipt. From JavaScript, in the browser or a server. Or using Capacitor or Electron. I've build integrations for everything. point-of-sale.dev

And you end up with bytes. Just raw bytes that you send to the printer - also with libraries that I created...

From the moment I've been working on this - 15 years ago - I've always wanted to build a decoder, so that I could inspect what we actually send to the printer... every single command that it receives.

But... what I really wanted is a renderer. For two reasons - some printers only support bitmaps, and I wanted to be able to print on those too. But I also wanted to have a preview to see how a receipt rendered.

And to render receipts, you need a bitmap font at specific sizes. And there wasn't yet one... So I created a bitmap font editor... I know 🤪

The result is a renderer that exactly matches a real printer. And it does not just support the code my own projects generate…

I generated receipts using a dozen different open-source encoders and test suites of other rendered and compared them manually with the output of dozens of printers. Painstakingly making sure to capture every single quirk and detail...