reMarkable tablet becomes Tom Riddle's diary: write in ink, an LLM writes back

A developer has built Riddle, an open-source hack that turns a reMarkable Paper Pro e-ink tablet into the enchanted diary from Harry Potter. You handwrite on the page with the stylus; after a short pause your ink fades away, a vision-capable language model reads the committed page as an image, and a reply appears letter by letter in a flowing script before dissolving. There is no chat window, keyboard, or screen glow — just ink surfacing on paper.

The project is technically ambitious. A Rust app captures raw pen input at full pressure sensitivity, rasterizes and skeletonizes handwriting into single-pixel pen paths (using Zhang-Suen thinning and stroke tracing), and animates the replies. For lowest latency it can run in a ‘takeover’ mode that stops the vendor UI and drives the e-ink waveform engine directly through a C shim that interposes on reMarkable’s proprietary libqsgepaper.so, hitting roughly one second to first ink on-device. The oracle backend is pluggable: any OpenAI-compatible vision endpoint (OpenAI, OpenRouter, Groq, Gemini, a local server) or a warm resident process, streaming responses sentence by sentence so the diary starts writing before the model finishes.

Beyond the novelty, it’s a notable example of the growing hobbyist scene modifying e-ink hardware. Setup requires developer mode plus the xovi/AppLoad launcher, and the author is blunt that it runs as root, drives hardware directly, is tested only on one specific model and OS range, and can brick the experience — keep SSH open as an escape hatch. The code is MIT-licensed, though the vendor Qt and e-ink libraries it hooks into must be pulled from the user’s own device.