What is riddle?

Riddle turns a reMarkable Paper Pro tablet into something like the diary of Tom Riddle from the Harry Potter books. You write on the screen with the tablet's pen, and after you pause for a couple of seconds, your handwritten words fade away as if the page absorbed the ink, then an answer writes itself back onto the page in flowing handwriting, one stroke at a time, before fading away too. There is no keyboard, no chat window, and no visible app interface, only ink appearing and disappearing on the page. The project is written in Rust and runs directly on the tablet. It captures raw pen input, including pressure detail, turns a finished page into an image, sends that image to an AI model that can read images, and converts the model's text reply into realistic handwritten strokes that animate onto the page. A companion project called Quill provides a low level way to draw directly on the tablet's e-ink screen for the fastest possible response. Beyond simple back and forth writing, the diary keeps a memory of every page you have written, including your original strokes and a transcription, so you can ask it in ink to recall something you wrote before, and it will rewrite that old page in your own handwriting, dated, in faded ink. You can also flip the pen's marker end to erase, draw a large question mark to bring up a built in guide, or tap the screen with five fingers to leave the diary and return to the normal tablet interface. To answer you, the diary connects to a vision capable AI model, either through any service that speaks the OpenAI style chat API, such as OpenAI, OpenRouter, or Groq, using your own API key, or through a separate tool called pi if you already run that. Setting it up requires putting the reMarkable Paper Pro into developer mode, installing a launcher, and either installing riddle through a companion tool called remagic or copying a prebuilt release onto the tablet by hand. The project is explicit that this modifies your device and is not affiliated with reMarkable, and that it has only been tested on that one specific tablet model.